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Dr. Lucia LEONAT

Scientific Researcher II

Laboratory of Complex Heterostructures and Multifunctional Materials

lucia[DOT]leonat[AT]infim[DOT]ro
Keywords: solar cells; perovskite; thin-films

Education

1.  Politehnica University, Bucharest, Faculty of Applied Chemistry and Materials Science; Ph.D. Degree,  MD.3930from 20.06.2013, focusing on the study of natural and nature-inspired materials for sustainable organic electronics, manufacturing, and characterization of solar cells and field-effect transistors with thin organic films.

 

2.  Johannes Kepler University, Linz, Austria, Linz Institute for Organic Solar Cells, Linz, Austria; Apr-Nov 2011; Ph.D. student internship in Organic electronics, to study some of the “unusual” materials for organic electronics, manufacturing, and characterization of solar cells and field-effect transistors with thin organic films, focusing on hydrogen-bonded molecules.

3. University of Bucharest, Faculty of Biology, Institute of Biodynamics; 2003-2005; Master Degree in Biodynamics.

 

4.  University of Bucharest, Faculty of Physics; 1998-2002; Academic Degree in Physics, Medical Physics.

Positions

1.  Current position, since Nov. 2016, Senior Researcher II, National Institute of Materials Physics (NIMP) Magurele: fundamental and applicative research in the field of organic/hybrid semiconductors, thin-film fabrication and characterization (SEM, AFM), fabrication and characterization of organic and perovskite solar cells with standard mesoscopic and inverted design;

2.  Jan. 2016 – Oct 2016, Senior Researcher II, National Institute for Electrical Engineering (INCDIE ICPE-CA) Bucharest: fundamental and applicative research in the field of bulk materials for electrical engineering: metallic – alloys, nanomaterials, ceramics, carbon fibers, nanotubes, graphene;

3.  2013-2015, Postdoctoral Fellow, Linz Institute for Organic Solar Cells, Johannes Kepler University, Linz, Austria: fabrication and characterization of organic polymer and small molecule thin-film solar cells on flexible, biodegradable substrates; fabrication and characterization of perovskite solar cells on flexible, ultrathin substrates;

4.  2006 - 2013, Research Assistant, INCDIE ICPE-CA Bucharest: fundamental and applicative research in the field of bulk materials and powders for electrical engineering: metallic – alloys, nanomaterials, ceramics, carbon-based materials (fibers, activated carbon, nanotubes, graphene), by physical-chemical characterizations: porosity measurements, thermal characterization, UV-Vis spectroscopy.

Expertize

Thin-film deposition by spin-coating, thermal vacuum evaporation, blade-coating;

Thin-film characterization by scanning electron microscopy (SEM), scanning probe microscopy (AFM), and UV-Vis spectrometry.

Hybrid and organic solar cell fabrication and characterization [electrical measurements (I/V curves) and external quantum efficiency (EQE)].

Patents

1. "Printer for succesive deposition of ultra-thin layers of different plysical-chemical properties", authors ILIESCU M; LAZAR M; PINTILIE I; VLADAREANU L; NECSOIU T; STANCU V; TOMULESCU A G; BESLEAGA S C; SIMA M; LEONAT L; STANCIU E M; COMANESCU B; ENUICA A V, A00195/2017, Hotarare 4/21 30.01.2019;

2. "Strat mezoporos pentru celule solare pe bază de perovskiți și metoda de obținere", authors PINTILIE I; TOMULESCU A G; LEONAT L N; STANCU V; BESLEAGA S C; TOMA V; DUMITRU V G; PINTILIE L, A00364/2018, Hotarare 3/124, 30.09.2019.

3. "Hybrid perovskite-based mini-solar module and corresponding encapsulation method", authors: L. N. LEONAT, A.-G. TOMULESCU, G. DOBRESCU, A. IGHIGEANU, M. LAZĂR, V. STANCU, V. TOMA, A/00625 from 12.10.2022.

 

Resume

Dr. Lucia Leonat, Scientific researcher rank II, graduated from the University of Bucharest, Faculty of Physics, Specialization, Medical Physics (2002), holds a MSc degree in Biodynamics (2005) from the University of Bucharest, Faculty of Biology, Specialization, Biodynamics and a PhD degree in Applied Chemistry and Materials Science from the Politehnica University of Bucharest, Faculty of Applied Chemistry and Materials Science (2013).

Work experience: National Institute of Electrical Engineering (ICPE-CA) (2006 - 2016); work and study stage and postdoc at the Johannes Kepler University from Linz, Austria and University of St Andrews, Scotland, UK; National Institute of Materials Physics (NIMP) (2016 – to date).

Main areas of interest/expertise: thin film fabrication (spincoating, slot-die, dr blade, spray coating, thermal evaporation), materials characterization (AFM, SEM), fabrication and characterization of organic and hybrid (perovskite) solar cells.

Publications (last updated November 2022): 45 articles published in Web of Science® (WoS); Hirsch index (WoS): 14; Citations (without self-citations): 1475.

Professional profile web-links: ResearcherID: N-6868-2016; ORCHID: https://orcid.org/0000-0002-7120-3644; Google Scholar: https://scholar.google.com/citations?user=PV_iCTQAAAAJ; Brainmap: https://www.brainmap.ro/lucia-nicoleta-leonat.

Patents: 5 awarded patents: RO127500-B1/2012; RO126305-A0/ 2015; RO125773-B1/2016;

RO132082-B1/2019; RO132815-A0/2019.

Coordinated projects: 2 national projects: PN-III-P2-2.1-PED-2019-1411; PN-III-P1-1.1-PD-2016-0703.

Projects

1. Solar mini-module with perovskite solar cells

Project Type: PED, Start Date: 2020-10-23 End Date: 2022-10-22

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Publications

1. Hindrances and solutions on the path towards adjoined barium titanate-hydroxyapatite ceramics with uncompromised piezoelectric and biological responses
Authors: Cioangher, M; Amarande, L; Stan, GE; Nedelcu, L; Pasuk, I; Leonat, L; Popa, AC; Miclea, LC; Savopol, T; Moisescu, MG; Tivig, I

Published: SEP 1 2024, CERAMICS INTERNATIONAL, 50, DOI: 10.1016/j.ceramint.2024.05.268

The synergistic piezoelectric and osteoconductive properties of barium titanate (BT) and hydroxyapatite (HA) could stir the development of a new generation of synthetic bone graft substitutes, with capability for rapid and safe osseointegration. The research focused on two concurrent approaches for coupling the BT and HA materials: (i) conventional sintering of BT-HA powder mixtures; and (ii) functionalization of pre-sintered BT with HA coatings using magnetron sputtering (MS). Irrespective of the BT/HA ratios ranging from 95/5 to 80/20 wt%, nanocrystalline or highly-crystallized nature of the powders, sub-micron- or micron-sized particle dimensions, and sintering temperature, it was observed that the BT-HA reactivity cannot be prevented above 800 degrees C. At higher temperatures in the range of 1000-1300 degrees C, HA undergoes decomposition and extensively reacts with BT, leading to the formation of several secondary phases such as CaTiO3, Ba2Ca(PO4)2, BaCa6(PO4)4O, BaCa(PO3)4, and beta-Ca2P2O7. As a consequence, the cytocompatibility assessed in fibroblast and osteoblast cell cultures, as well as the piezoelectric response, were significantly altered. Applying HA coatings by MS to the sintered BT ceramics successfully preserved their piezoelectric properties, while also providing an unaltered cytocompatible and osteogenic-prone surface. The HA coatings were fully crystallized at post-deposition annealing temperatures of 550 and 700 degrees C, achieving crystalline qualities comparable to HA powders sintered at 1100 and 1200 degrees C, respectively. No reactivity events between BT and HA were observed. Partial reactivity was only noticeable upon annealing at 1000 degrees C. Therefore, it is suggested that the HA coating of BT is effective in seamlessly coupling the piezoelectric and osteogenic properties of the two constituents without compromise.
2. Effect of transition metal ions on the dielectric properties of chromium potassium phosphates
Authors: Mighri, Z; Patru, RE; Leonat, LN; El Khouja, O; Nasri, H; Rostas, AM; Galca, AC

Published: DEC 25 2024, JOURNAL OF ALLOYS AND COMPOUNDS, 1009, 176870, DOI: 10.1016/j.jallcom.2024.176870

Potassium ions are important for developing electrode materials because they have similar properties to lithium and sodium ions. Mixed chromium phosphates (KMIICr(PO4)2) II Cr (PO 4 ) 2 ) with substituted M II sites using divalent elements (M = Ni, Co, Cu) were synthesized using a solid-state reaction method. The samples were analyzed using various techniques such as powder X-ray diffraction, Fourier transform infrared, Raman, and electron paramagnetic resonance spectroscopy. The proposed phosphates had a monoclinic phase structure with a P21/n 1 /n space group, and they contained large tunnels occupied by K+ + cations. The dielectric properties showed that the Ni-based phosphates had slower dielectric relaxation, while the Co and Cu-based phosphates had quicker polarization and depolarization processes. Additionally, the resistance of the grains decreased from Ni to Co to Cu-based phosphates, indicating easier charge movement in each material, consistent with the increase in conductive losses and a.c. conductivity when changing the M II ions.
3. Hybrid supercapacitors based on X-site Ba(II) ions substituted by Sr(II) in Langbeinite-type phosphates
Authors: Mighri, Z; Yildirim, ID; Leonat, LN; El Khouja, O; Erdem, E; Nasri, H; Galca, AC; Rostas, AM

Published: AUG 2024, MATERIALIA, 36, 102147, DOI: 10.1016/j.mtla.2024.102147

The compounds KBa 1-x Sr x Cr 2 (PO 4 ) 3 (with x = 0.00; 0.25; 0.50; 0.75; 1.00) were synthesized by a solid-state reaction, and they were thoroughly characterized by different spectroscopic and microscopic techniques. Their structures were indexed in a cubic system with a P2 1 3 space group forming a 3D framework built on CrO 6 octahedra and PO 4 tetrahedra sharing vertices leading to identical Cr 2 P 3 O 18 (U) units. The interconnection between the tetrahedral and octahedral groups leads to the formation of two large closed cavities (K, M II )(1) and (K, M II )(2), statistically occupied by K + and M 2+ (M = Ba, Sr) atoms. Electron paramagnetic resonance spectroscopy confirmed the presence of paramagnetic Cr 3+ ions, showing the effects of substituting the Ba 2+ ions with smaller Sr 2+ ions on the dipolar coupling between the Cr 3+ centers. The obtained materials and active carbon were used as electrode materials in hybrid SC devices. At the same time, their electrochemical properties were assessed by potentiostatic electrochemical impedance spectroscopy, cyclic voltammetry, and galvanostatic charge-discharge measurements, showing promising results with a maximal specific capacitance (3.86 F/g), energy density (343 mWh/kg), and power density (30.9 kW/kg) in the case of KBa 0.5 Sr 0.5 Cr 2 (PO 4 ) 3 , proving them as good candidates for positive and/or negative electrode materials for energy storage applications.
4. Multi-Parametric Exploration of a Selection of Piezoceramic Materials for Bone Graft Substitute Applications
Authors: Nedelcu, L; Ferreira, JMF; Popa, AC; Amarande, L; Nan, B; Balescu, LM; Geambasu, CD; Cioangher, MC; Leonat, L; Grigoroscuta, M; Cristea, D; Stroescu, H; Ciocoiu, RC; Stan, GE

Published: FEB 2023, MATERIALS, 16, 901, DOI: 10.3390/ma16030901

This work was devoted to the first multi-parametric unitary comparative analysis of a selection of sintered piezoceramic materials synthesised by solid-state reactions, aiming to delineate the most promising biocompatible piezoelectric material, to be further implemented into macro-porous ceramic scaffolds fabricated by 3D printing technologies. The piezoceramics under scrutiny were: KNbO3, LiNbO3, LiTaO3, BaTiO3, Zr-doped BaTiO3, and the (Ba0.85Ca0.15)(Ti0.9Zr0.1)O-3 solid solution (BCTZ). The XRD analysis revealed the high crystallinity of all sintered ceramics, while the best densification was achieved for the BaTiO3-based materials via conventional sintering. Conjunctively, BCTZ yielded the best combination of functional properties-piezoelectric response (in terms of longitudinal piezoelectric constant and planar electromechanical coupling factor) and mechanical and in vitro osteoblast cell compatibility. The selected piezoceramic was further used as a base material for the robocasting fabrication of 3D macro-porous scaffolds (porosity of similar to 50%), which yielded a promising compressive strength of similar to 20 MPa (higher than that of trabecular bone), excellent cell colonization capability, and noteworthy cytocompatibility in osteoblast cell cultures, analogous to the biological control. Thereby, good prospects for the possible development of a new generation of synthetic bone graft substitutes endowed with the piezoelectric effect as a stimulus for the enhancement of osteogenic capacity were settled.
5. Partial replacement of Pb2+ in MAPbI(2.6)Cl(0.4) perovskite films and their photovoltaic performance
Authors: Derbali, S; Nouneh, K; Leonat, LN; Stancu, V; Tomulescu, AG; Galca, AC; Touhami, ME; Pintilie, I; Florea, M

Published: APR 2023, JOURNAL OF MATERIALS SCIENCE-MATERIALS IN ELECTRONICS, 34, 903, DOI: 10.1007/s10854-023-10318-9

Replacing lead atoms in halide perovskite materials is of significant importance for the development of environmentally friendly perovskite solar cells. In this paper, we investigated the effect of doping the MAPbI(2.6)Cl(0.4) hybrid perovskite (MA-methyl ammonium) with non-toxic elements, such as alkaline earth metal ions (Mg2+) and transition metal ions (Zn2+). The structural, morphological, and optical properties of the prepared samples were analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), and UV-Vis. spectroscopy. Finally, the doped films were used as photoactive layers in solar devices in order to evaluate their photovoltaic performance. Zn proved to be more appropriate to replace partially Pb and films with higher quality were obtained. As a result, the MAPb1(-x)Zn(x)I(2.6)Cl(0.4) based solar cells have demonstrated a slight improvement of the photovoltaic performances, resulting in a uniform and narrower PCEs (power conversion efficiency) range, compared to pristine MAPbI(2.6)Cl(0.4) based devices.
6. Partial Replacement of Dimethylformamide with Less Toxic Solvents in the Fabrication Process of Mixed-Halide Perovskite Films
Authors: Stancu, V; Tomulescu, AG; Leonat, LN; Balescu, LM; Galca, AC; Toma, V; Besleaga, C; Derbali, S; Pintilie, I

Published: FEB 2023, COATINGS, 13, 378, DOI: 10.3390/coatings13020378

The technology of perovskite solar cells (PSC) is getting close to breaching the consumer market. Yet, one of the current challenges is to reduce the toxicity during their fabrication by reducing the use of the toxic solvents involved in the perovskite fabrication process. A good solubilization of lead halides used in hybrid perovskite preparation is required, and it is only possible with polar solvents. A mixture of dimethylformamide (DMF) and dimethyl sulfoxide (DMSO) is the most popular solvent combination for a perovskite precursor solution. DMF is necessary to ensure a good dissolution of lead iodide, but it is also the most toxic solvent. In this paper, we study the replacement of the dimethylformamide with presumably less toxic alternatives, such as N-methyl-2-Pyrrolidone (NMP) and ethyl acetate (EA), for the preparation of the K(0.1)FA(0.7)MA(0.2)PbI(2.8)Cl(0.2) (KFAMA) hybrid perovskite. The perovskite thin films were investigated by various characterization techniques: X-ray diffraction, atomic force microscopy, scanning electron microscopy, and UV-vis spectroscopy, while the photovoltaic parameters were determined by measuring the IV curves of the corresponding solar cells. The present study shows that by keeping the same deposition parameters as when only DMF solvent is used, the partial solvent substitution with NMP and EA gives promising results for reducing the toxicity of the fabrication process of KFAMA-based PSCs. Thus, with no specific optimization of the deposition process, and for the maximum possible partial substitution of DMF with NMP and EA solvents, the loss in the power conversion efficiency (PCE) value is only 35% and 18%, respectively, associated with the more structural defects promoted by NMP and EA.
7. Structural and Electrical Properties of Novel Cr/Fe Mixed Transition-Metal Phosphates
Authors: Mighri, Z; Souiwa, K; Rostas, AM; Patru, RE; Bocirnea, AE; Iacob, N; Kuncser, V; El Khouja, O; Leonat, LN; Hidouri, M; Nasri, H; Galca, AC

Published: 2023 MAY 24 2023, INORGANIC CHEMISTRY, DOI: 10.1021/acs.inorgchem.2c04389

The phosphate KCoCr-(PO4)(2) and iron-substitutedvariants KCoCr1-x Fe x (PO4)(2) (x =0.25, 0.5, and 0.75) were synthesized by a solid-state reaction route,while a high substitution level of Fe was achieved. Their structureswere refined using powder X-ray diffraction and indexed in a monoclinicsystem with a P2(1)/n spacegroup. A 3D framework with six-sided tunnels parallel to the [101]direction was formed in which the K atoms are located. Mo''ssbauerspectroscopy confirms the exclusive presence of octahedral paramagneticFe(3+) ions, with isomer shifts increasing slightly with x substitution. Electron paramagnetic resonance spectroscopyconfirmed the presence of paramagnetic Cr3+ ions. The activationenergy, determined by dielectric measurements, shows that the iron-containingsamples present higher ionic activity. Relative to the electrochemicalactivity of K, these materials could be good candidates for positiveand/or negative electrode materials for energy storage applications. The synthesized phosphate KCoCr-(PO4)(2) and Fe-substituted variants KCoCr1-x Fe x (PO4)(2) (x = 0.25, 0.5, and 0.75) present a 3D frameworkwith six-sided tunnels in which the K atoms are located. The activationenergy, determined by dielectric measurements, shows that the iron-containingsamples present improved ionic activity, making these materials goodcandidates for positive and/or negative electrode materials for energystorage applications.
8. Partial replacement of Pb2+ in MAPbI2.6Cl0.4 perovskite films and their photovoltaic performance
Authors: Derbali, S; Nouneh, K; Leonat, LN; Stancu, V; Tomulescu, AG; Galca, AC; Touhami, ME; Pintilie, I; Florea, M

Published: APR 2023, JOURNAL OF MATERIALS SCIENCE-MATERIALS IN ELECTRONICS, 34, 903, DOI: 10.1007/s10854-023-10318-9

Replacing lead atoms in halide perovskite materials is of significant importance for the development of environmentally friendly perovskite solar cells. In this paper, we investigated the effect of doping the MAPbI(2.6)Cl(0.4) hybrid perovskite (MA-methyl ammonium) with non-toxic elements, such as alkaline earth metal ions (Mg2+) and transition metal ions (Zn2+). The structural, morphological, and optical properties of the prepared samples were analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), and UV-Vis. spectroscopy. Finally, the doped films were used as photoactive layers in solar devices in order to evaluate their photovoltaic performance. Zn proved to be more appropriate to replace partially Pb and films with higher quality were obtained. As a result, the MAPb1(-x)Zn(x)I(2.6)Cl(0.4) based solar cells have demonstrated a slight improvement of the photovoltaic performances, resulting in a uniform and narrower PCEs (power conversion efficiency) range, compared to pristine MAPbI(2.6)Cl(0.4) based devices.
9. Structural and Electrical Properties of Novel Cr/Fe Mixed Transition-Metal Phosphates
Authors: Mighri, Z; Souiwa, K; Rostas, AM; Patru, RE; Bocirnea, AE; Iacob, N; Kuncser, V; El Khouja, O; Leonat, LN; Hidouri, M; Nasri, H; Galca, AC

Published: MAY 24 2023, INORGANIC CHEMISTRY, 62, DOI: 10.1021/acs.inorgchem.2c04389

The phosphate KCoCr-(PO4)(2) and iron-substitutedvariants KCoCr1-x Fe x (PO4)(2) (x =0.25, 0.5, and 0.75) were synthesized by a solid-state reaction route,while a high substitution level of Fe was achieved. Their structureswere refined using powder X-ray diffraction and indexed in a monoclinicsystem with a P2(1)/n spacegroup. A 3D framework with six-sided tunnels parallel to the [101]direction was formed in which the K atoms are located. Mo''ssbauerspectroscopy confirms the exclusive presence of octahedral paramagneticFe(3+) ions, with isomer shifts increasing slightly with x substitution. Electron paramagnetic resonance spectroscopyconfirmed the presence of paramagnetic Cr3+ ions. The activationenergy, determined by dielectric measurements, shows that the iron-containingsamples present higher ionic activity. Relative to the electrochemicalactivity of K, these materials could be good candidates for positiveand/or negative electrode materials for energy storage applications. The synthesized phosphate KCoCr-(PO4)(2) and Fe-substituted variants KCoCr1-x Fe x (PO4)(2) (x = 0.25, 0.5, and 0.75) present a 3D frameworkwith six-sided tunnels in which the K atoms are located. The activationenergy, determined by dielectric measurements, shows that the iron-containingsamples present improved ionic activity, making these materials goodcandidates for positive and/or negative electrode materials for energystorage applications.
10. Effect of chlorine and bromine on the perovskite crystal growth in mesoscopic heterojunction photovoltaic device
Authors: Mehdi, H; Leonat, LN; Stancu, V; Saidi, H; Enculescu, M; Tomulescu, AG; Toma, V; Pintilie, I; Bouazizi, A; Galca, AC

Published: JUN 1 2022, MATERIALS SCIENCE IN SEMICONDUCTOR PROCESSING, 143, 106558, DOI: 10.1016/j.mssp.2022.106558

Organic-inorganic hybrid perovskite solar cells are within the emerging photovoltaic technologies. The combination of different halogen ions, in certain fill fractions, is one of the methods to improve the perovskite film properties. Herein, fabrication and characterization of perovskite cells in standard mesoscopic architecture using one-step deposition method has been done. The role of the halogen ions (Chlorine or Bromine) on crystal structure growth and photoelectric performance has been investigated. X-ray diffraction, scanning electron microscopy, atomic force microscopy and optical microscopy analysis were performed. The microstructure, composition and morphology of CH3NH3PbI1.8Br1.2 and CH3NH3PbI1.8Cl1.2 films are dissimilar, although identical fabrication method was used. Same holds for optical properties, band gap energies of 1.84 eV and 1.63 eV, respectively, being obtained. Integrated in solar cells, the maximum power conversion efficiency of the Br based devices is beyond 10%, while for those based on Cl, the efficiency drops around 5%.
11. Sr and Mg Doped Bi-Phasic Calcium Phosphate Macroporous Bone Graft Substitutes Fabricated by Robocasting: A Structural and Cytocompatibility Assessment
Authors: Besleaga, C; Nan, B; Popa, AC; Balescu, LM; Nedelcu, L; Neto, AS; Pasuk, I; Leonat, L; Popescu-Pelin, G; Ferreira, JMF; Stan, GE

Published: SEP 2022, JOURNAL OF FUNCTIONAL BIOMATERIALS, 13, 123, DOI: 10.3390/jfb13030123

Bi-phasic calcium phosphates (BCPs) are considered prominent candidate materials for the fabrication of bone graft substitutes. Currently, supplemental cation-doping is suggested as a powerful path to boost biofunctionality, however, there is still a lack of knowledge on the structural role of such substituents in BCPs, which in turn, could influence the intensity and extent of the biological effects. In this work, pure and Mg- and Sr-doped BCP scaffolds were fabricated by robocasting from hydrothermally synthesized powders, and then preliminarily tested in vitro and thoroughly investigated physically and chemically. Collectively, the osteoblast cell culture assays indicated that all types of BCP scaffolds (pure, Sr- or Sr-Mg-doped) delivered in vitro performances similar to the biological control, with emphasis on the Sr-Mg-doped ones. An important result was that double Mg-Sr doping obtained the ceramic with the highest beta-tricalcium phosphate (beta-TCP)/hydroxyapatite mass concentration ratio of similar to 1.8. Remarkably, Mg and Sr were found to be predominantly incorporated in the beta-TCP lattice. These findings could be important for the future development of BCP-based bone graft substitutes since the higher dissolution rate of beta-TCP enables an easier release of the therapeutic ions. This may pave the road toward medical devices with more predictable in vivo performance.
12. Electrochemical and In Vitro Biological Evaluation of Bio-Active Coatings Deposited by Magnetron Sputtering onto Biocompatible Mg-0 .8Ca Alloy
Authors: Bita, AI; Antoniac, I; Miculescu, M; Stan, GE; Leonat, L; Antoniac, A; Constantin, B; Forna, N

Published: MAY 2022, MATERIALS, 15, 3100, DOI: 10.3390/ma15093100

The use of resorbable magnesium alloys in the design of implants represents a new direction in the healthcare domain. Two main research avenues are currently explored for developing or improving metallic biomaterials: (i) increase of their corrosion resistance by designed compositional and structural modifications, and (ii) functionalization of their surfaces by coating with ceramic or polymeric layers. The main objective of this work was to comparatively assess bio-functional coatings (i.e., highly-crystallized hydroxyapatite and silica-rich glass) deposited by radio-frequency magnetron sputtering (RF-MS) on a biodegradable Mg-0.8Ca alloy (0.8 wt.% of Ca). After probing their morphology (by scanning electron microscopy) and structure (by Fourier transform infrared spectroscopy and grazing incidence X-ray diffraction), the corrosion resistance of the RF-MS coated Mg-0.8Ca substrates was electrochemically tested (in synthetic biological media with different degrees of biomimicry), and their cytocompatibility was assessed in osteoblast and fibroblast cell cultures. By collective assessment, the most promising performances, in terms of mass loss (similar to 7% after 12 days), hydrogen release rate (similar to 6 mL/cm(2) after 12 days), electrochemical corrosion parameters and cytocompatibility, were obtained for the crystalline HA coating.
13. Potassium-containing triple-cation mixed-halide perovskite materials: Toward efficient and stable solar cells
Authors: Derbali, S; Nouneh, K; Florea, M; Leonat, LN; Stancu, V; Tomulescu, AG; Galca, AC; Secu, M; Pintilie, L; Touhami, ME

Published: MAR 25 2021, JOURNAL OF ALLOYS AND COMPOUNDS, 858, DOI: 10.1016/j.jallcom.2020.158335

In this paper, potassium based triple cation mixed-halide perovskite films were explored in order to enhance the stability and photovoltaic performance of perovskite based solar cells. It was found that adding potassium (K+) to a double cation mixed halide perovskite (FA(0.80)MA(0.20)PbI(2.8)Cl(0.2)), structural, morphological and optoelectronic properties of perovskites are improved. The perovskite films were prepared by one-step spin coating method with and without K+ and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), UV-Vis spectroscopy, X-ray photoelectron spectroscopy (XPS), and photoluminescence spectroscopy (PL). The results indicate that potassium incorporation reduces significantly the yellow non-perovskite delta-phase formation and improves the perovskite film quality, thus contributing to the reduction of hysteresis, improves the stability and increases the PCE up to 12.51%. Furthermore, the doped devices exhibit reduced hysteresis and provide remarkable shelf stability by retaining more than 70% of the initial efficiency with low humidity over 850 h. (C) 2020 Elsevier B.V. All rights reserved.
14. Enhancing stability of hybrid perovskite solar cells by imidazolium incorporation
Authors: Tomulescu, AG; Leonat, LN; Neatu, F; Stancu, V; Toma, V; Derbali, S; Neatu, S; Rostas, AM; Besleaga, C; Patru, R; Pintilie, I; Florea, M

Published: AUG 1 2021, SOLAR ENERGY MATERIALS AND SOLAR CELLS, 227, DOI: 10.1016/j.solmat.2021.111096

Hybrid perovskites based solar cells have demonstrated high conversion efficiency but poor long-term stability. This study reports on the results obtained after doping the CH3NH3PbI2.6Cl0.4 mixed halide perovskite with imidazolium (C3N2H5+, denoted IM) on the "A site" position of a perovskite, to improve photovoltaic performances and stability of hybrid perovskite solar cells. The perovskite films were investigated exhaustively by different characterization techniques: X-ray diffraction, Atomic Force Microscopy, Scanning Electron Microscopy, UV-Vis, X-ray Photoelectron Electron Paramagnetic Resonance spectroscopies, Impedance Spectroscopy and Incident Photon-to-Electron Conversion Efficiency. The photovoltaic parameters were determined by measuring the IV curves of the corresponding solar cells. The amount of IM inserted in the perovskite play a key role on the film properties. The calculated new tolerance factors according to the "globularity factor" are experimentally proved and thus at doping concentrations greater than 20% for CH3NH3PbI2.6Cl0.4 perovskite the 3D structure is no longer obtained. However, below this value, the IM substituted perovskite film possesses an improved film quality and crystallinity as compared to the pristine film. Substituting MA+ with IM+ provides a favorable way to reduce recombination processes and shows great potential to achieve high stability, and an improved charge generation, resulting in increased PCE values. We find that the optimal percentage of imidazolium incorporation to achieve better stability of solar cells is 6%.
15. Strippable Polymeric Nanocomposites Comprising "Green" Chelates, for the Removal of Heavy Metals and Radionuclides
Authors: Toader, G; Pulpea, D; Rotariu, T; Diacon, A; Rusen, E; Moldovan, A; Podaru, A; Ginghina, R; Alexe, F; Iorga, O; Bajenaru, SA; Ungureanu, M; Dirloman, F; Pulpea, B; Leonat, L

Published: DEC 2021, POLYMERS, 13, DOI: 10.3390/polym13234194

The issue of heavy metal and radionuclide contamination is still causing a great deal of concern worldwide for environmental protection and industrial sites remediation. Various techniques have been developed for surface decontamination aiming for high decontamination factors (DF) and minimal environmental impact, but strippable polymeric nanocomposite coatings are some of the best candidates in this area. In this study, novel strippable coatings for heavy metal and radionuclides decontamination were developed based on the film-forming ability of polyvinyl alcohol, with the remarkable metal retention capacity of bentonite nanoclay, together with the chelating ability of sodium alginate and with "new-generation" "green" complexing agents: iminodisuccinic acid (IDS) and 2-phosphonobutane-1,2,4-tricarboxylic acid (PBTC). These environmentally friendly water-based decontamination solutions are capable of generating strippable polymeric films with optimized mechanical and thermal properties while exhibiting high decontamination efficiency (DF approximate to 95-98% for heavy metals tested on glass surface and DF approximate to 91-97% for radionuclides Am-241, Sr-90-Y and Cs-137 on metal, painted metal, plastic, and glass surfaces).
16. Influence of doping the inorganic cation with Eu or Sb on the properties of perovskite films
Authors: Stancu, V; Leonat, LN; Tomulescu, AG; Derbali, S; Pintilie, L; Besleaga, C; Galca, AC; Neatu, F; Neatu, T; Florea, M; Pintilie, I

Published: JUL 2020, PHYSICA SCRIPTA, 95, DOI: 10.1088/1402-4896/ab90be

This study reports on the results obtained after doping the [CH3NH3](0.94)[C3N2H5](0.06)PbI2.6Cl0.4 mixt halide perovskite with europium or antimony (Eu3+/Sb3+) at the 'B site'. This way two new complex compounds were obtained, [CH3NH3](0.94)[C3N2H5](0.06)Pb1-yByI2.6Cl0.4 (B = Eu or Sb and y = 0-0.05) as perovskite precursor solutions and deposited as thin films. The properties of the perovskite films were investigated by various characterization techniques: x-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM), UV-vis spectroscopy while the photovoltaic parameters were determined by measuring the IV curves of the corresponding solar cells. We find that doping the mixt halide perovskite with very small quantities of Sb improves the quality of the perovskite films and further improves the stability of perovskite solar cells.
17. Highly Active Transition Metal-Promoted CuCeMgAlO Mixed Oxide Catalysts Obtained from Multicationic LDH Precursors for the Total Oxidation of Methane
Authors: Al-Aani, HMS; Trandafir, MM; Fechete, I; Leonat, LN; Badea, M; Negrila, C; Popescu, I; Florea, M; Marcu, IC

Published: JUN 2020, CATALYSTS, 10, DOI: 10.3390/catal10060613

To improve the catalytic performance of an active layered double hydroxide (LDH)-derived CuCeMgAlO mixed oxide catalyst in the total oxidation of methane, it was promoted with different transition-metal cations. Thus, two series of multicationic mixed oxides were prepared by the thermal decomposition at 750 degrees C of their corresponding LDH precursors synthesized by coprecipitation at constant pH of 10 under ambient atmosphere. The first series of catalysts consisted of four M(3)CuCeMgAlO mixed oxides containing 3 at.% M (M = Mn, Fe, Co, Ni), 15 at.% Cu, 10 at.% Ce (at.% with respect to cations), and with Mg/Al atomic ratio fixed to 3. The second series consisted of four Co(x)CuCeMgAlO mixed oxides withx= 1, 3, 6, and 9 at.% Co, while keeping constant the Cu and Ce contents and the Mg/Al atomic ratio. All the mixed oxides were characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM) coupled with X-ray energy dispersion analysis (EDX), X-ray photoelectron spectroscopy (XPS), nitrogen adsorption-desorption at -196 degrees C, temperature-programmed reduction under hydrogen (H-2-TPR), and diffuse reflectance UV-VIS spectroscopy (DR UV-VIS), while thermogravimetric and differential thermal analyses (TG-DTG-DTA) together with XRD were used for the LDH precursors. The catalysts were evaluated in the total oxidation of methane, a test reaction for volatile organic compounds (VOC) abatement. Their catalytic performance was explained in correlation with their physicochemical properties and was compared with that of a reference Pd/Al(2)O(3)catalyst. Among the mixed oxides studied, Co(3)CuCeMgAlO was found to be the most active catalyst, with a temperature corresponding to 50% methane conversion (T-50) of 438 degrees C, which was only 19 degrees C higher than that of a reference Pd/Al(2)O(3)catalyst. On the other hand, this T(50)value was ca. 25 degrees C lower than that observed for the unpromoted CuCeMgAlO system, accounting for the improved performance of the Co-promoted catalyst, which also showed a good stability on stream.
18. Exploring the effect of aliovalent substitution of Pb2+ by Eu3+ on structural, morphological and optical properties of CH3NH3PbI3 perovskite films
Authors: Derbali, S; Nouneh, K; Florea, M; Neatu, F; Neatu, S; Leonat, LN; Secu, M; Tomulescu, AG; Stancu, V; Pintilie, L; Touhami, ME; Galca, AC

Published: APR 2020, PHYSICA SCRIPTA, 95, DOI: 10.1088/1402-4896/ab5baa

In this work, the effect of aliovalent substitution of Pb2+ by Eu3+ on structural, morphological and optical properties of CH3NH3PbI3 (MAPbI(3)) was studied, aiming to improve the properties of perovskite films used in solar cells application. The surface morphology, the microstructure and the optical properties of the obtained films containing different Europium (Eu) concentrations were characterized by atomic force microscopy, x-ray photoelectron spectroscopy, x-ray diffraction, UV-vis spectroscopy and photoluminescence spectroscopy.
19. Reticulated Mesoporous TiO2 Scaffold, Fabricated by Spray Coating, for Large-Area Perovskite Solar Cells
Authors: Tomulescu, AG; Stancu, V; Besleaga, C; Enculescu, M; Nemnes, GA; Florea, M; Dumitru, V; Pintilie, L; Pintilie, I; Leonat, L

Published: JAN 2020, ENERGY TECHNOLOGY, 8, DOI: 10.1002/ente.201900922

Development of reproducible, low-cost fabrication technologies that are readily adaptable to large-scale production, is one of the main challenges in the field of perovskite solar cells (PSCs). So far, for all the other layers in a solar cell, large-area deposition methods have been adapted, except for mesoporous fabrication. Herein, the fabrication of mesoporous TiO2 scaffolds using a large-area deposition technique, such as spray coating, is shown. Moreover, this technique induces the formation of a very specific reticulated structure with well-delimited, oval-shaped cavities. The cavities have irregular dimensions, with diameters in the range of 3-7 mu m, approximate to 350 nm height, resulting in an overall increase in roughness of one order of magnitude, compared with the spin-coated mesoporous scaffold. Using this rough structured mesoporous TiO2 in PSCs not only does not affect the efficiency of solar cells but actually improves it from an average of 10% to 12% in comparison with the devices containing a spin-coated mesoporous scaffold.
20. Bulk Versus Surface Modification of Alumina with Mn and Ce Based Oxides for CH4 Catalytic Combustion
Authors: Neatu, S; Trandafir, MM; Stanoiu, A; Florea, OG; Simion, CE; Leonat, LN; Cobianu, C; Gheorghe, M; Florea, M; Neatu, F

Published: JUN 1 2019, MATERIALS, 12, DOI: 10.3390/ma12111771

This study presents the synthesis and characterization of lanthanum-modified alumina supported cerium-manganese mixed oxides, which were prepared by three different methods (coprecipitation, impregnation and citrate-based sol-gel method) followed by calcination at 500 degrees C. The physicochemical properties of the synthesized materials were investigated by various characterization techniques, namely: nitrogen adsorption-desorption isotherms, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and H-2-temperature programmed reduction (TPR). This experimental study demonstrated that the role of the catalytic surface is much more important than the bulk one. Indeed, the incipient impregnation of CeO2-MnOx catalyst, supported on an optimized amount of 4 wt.% La2O3-Al2O3, provided the best results of the catalytic combustion of methane on our catalytic micro-convertors. This is mainly due to: (i) the highest pore size dimensions according to the Brunauer-Emmett-Teller (BET) investigations, (ii) the highest amount of Mn4+ or/and Ce4+ on the surface as revealed by XPS, (iii) the presence of a mixed phase (Ce2MnO6) as shown by X-ray diffraction; and (iv) a higher reducibility of Mn4+ or/and Ce4+ species as displayed by H-2-TPR and therefore more reactive oxygen species.
21. Comparison between dielectric and pyroelectric properties of PZFNT and BST type ceramics
Authors: Stancu, V; Amarande, L; Botea, M; Iuga, A; Leonat, LN; Tomulescu, AG; Cioangher, M; Balescu, LM; Pintilie, L

Published: 2019, PROCESSING AND APPLICATION OF CERAMICS, 13, 276, DOI: 10.2298/PAC1903269S

Ba0.75Sr0.25TiO3 (BST) and PbZr0.68Fe0.14Nb0.14Ti0.04O3 (PZFNT) ceramic pellets were obtained by ceramic technology and their structural, ferroelectric and pyroelectric properties were investigated. The relative density of BST and PZFNT is about 93% and 90%, respectively, with an average grain size of 102 mu m and 6.45 mu m. Both materials have similar room temperature dielectric constants (similar to 2000), but PZFNT shows higher remnant polarization (similar to 15 mu C/cm(2)) and better pyroelectric properties (similar to 1.69 . 10(-4) C/m(2)K), which recommend it for pyroelectric detectors, infrared radiation- and laser pulse energy-meters.
22. Carbon-based sprayed electrodes for pyroelectric applications
Authors: Chirila, C; Botea, M; Iuga, A; Tomulescu, AG; Balescu, L; Galca, AC; Boni, AG; Leonat, L; Pintilie, I; Pintilie, L

Published: AUG 15 2019, PLOS ONE, 14, DOI: 10.1371/journal.pone.0221108

A carbon-based layer was deposited by spraying on top of a ferroelectric layer grown by sol-gel on Si (001) substrate and its properties as electrode and absorber for pyroelectric detection were tested. It was found that the electric properties of the ferroelectric capacitor with top carbon-based sprayed electrode (CBSE) are comparable with those of the capacitors with standard top SrRuO3 (SRO)/Au electrode. Pyroelectric measurements show that the pyroelectric signal recorded on ferroelectric capacitors with top CBSE electrode is 2.5 times greater than for top SRO/Au electrode for low frequency range. The value of the pyroelectric coefficient was estimated to 9.73.10(-4) C/m(2)K for CBSE electrodes and 3.36.10(-4) C/m(2)K for SRO/Au respectively. The fabrication process of CBSE is of low cost, easy to implement and with high throughput making it attractive for manufacturing various devices like pyroelectric detector, thermal imaging, solar cells, etc.
23. Structural and optical properties of ZnO thin films grown by rapid atmospheric mist chemical vapor technique
Authors: Derbali, S; Nouneh, K; Galca, AC; Touhami, ME; Secu, M; Matei, E; Leonat, LN; Pintilie, L; El Harfaoui, N; Fahoume, M

Published: JUL 2019, OPTICAL AND QUANTUM ELECTRONICS, 51, DOI: 10.1007/s11082-019-1937-2

In this work, the effect of deposition time on the structural and optical properties of ZnO films deposited by Ultrasonic Spray Mist-CVD was studied aiming the application in perovskite solar cells, as holes blocking layer. Crystallinity, surface morphology and optical properties of the ZnO films were investigated by X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM), conventional and Photoluminescence (PL) spectroscopies, respectively. The XRD measurement proves the existence of the hexagonal wurtzite phase and a high degree of crystallinity with [001] preferential orientation. The SEM study shows that the films possess a compact structure. Smooth and homogenous surface was confirmed also by AFM. The obtained results indicate that ZnO films deposited by a simple, safe and cost-effective method present a great potential for application in perovskite solar cells.
24. The hysteresis-free behavior of perovskite solar cells from the perspective of the measurement conditions
Authors: Nemnes, GA; Besleaga, C; Tomulescu, AG; Leonat, LN; Stancu, V; Florea, M; Manolescu, A; Pintilie, I

Published: MAY 14 2019, JOURNAL OF MATERIALS CHEMISTRY C, 7, 5274, DOI: 10.1039/c8tc05999c

We investigate how far the hysteresis-free behavior of perovskite solar cells can be reproduced using particular pre-conditioning and measurement conditions. As there are currently more and more reports of perovskite solar cells without J-V hysteresis it is crucial to distinguish between genuine performance improvements and measurement artifacts. We focus on two of the parameters that influence the dynamic J-V scans, namely the bias scan rate and the bias poling voltage, and point out measurement conditions for achieving a hysteresis-free behavior. In this context we discuss the suitability of defining a hysteresis index (HI) for the characterization of dynamic J-V scans. Using HI, aging effects are also investigated, establishing a potential connection between the sample degradation and the variation of the maximal hysteresis on one hand, and the relaxation time scale of the slow process on the other hand. Pre-poling induced recombination effects are identified. In addition, our analysis based on sample pre-biasing reveals potential indications regarding two types of slow processes, with two different relaxation time scales, which provides further insight regarding ionic migration.
25. Stable Hall voltages in presence of dynamic quasi-continuum bands in poly (3,4-ethylene-dioxythiophene)
Authors: Stadler, P; Leonat, LN; Menon, R; Coskun, H; van Frank, S; Rankl, C; Scharber, MC

Published: FEB 2019, ORGANIC ELECTRONICS, 65, 418, DOI: 10.1016/j.orgel.2018.12.001

Topological and thermal disorder complicate the mobility characterization in poly(3,4-ethylenedioxythiophene) systems and presently leaves the exact transport mechanisms not fully understood. Here we show that ac-Hall measured by lock-in amplifier is able to resolve the Hall voltage in semimetallic polymers between room temperature and 32 K. These results are evaluated using an organic random phase model. This accounts for the role of tail states and, particularly, for thermal disorder of molecular semiconductors. We report band mobilities up to 3.7 cm(2) V-1 s(-1) in semimetallic polymers occurring in delocalized bands that originate from significant electron coherence across the polymer chains.
26. X Ray study of GZO thin films
Authors: Sbarcea, BG; Prepelita, P; Leonat, LN

Published: AUG 2018, ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES, 74, E287, DOI: 10.1107/S2053273318090848

27. Normal and Inverted Hysteresis in Perovskite Solar Cells
Authors: Nemnes, GA; Besleaga, C; Stancu, V; Dogaru, DE; Leonat, LN; Pintilie, L; Torfason, K; Ilkov, M; Manolescu, A; Pintilie, I

Published: JUN 1 2017, JOURNAL OF PHYSICAL CHEMISTRY C, 121, 11214, DOI: 10.1021/acs.jpcc.7b04248

Hysteretic effects are investigated in perovskite solar cells in the standard FTO/TiO2/CH3NH3PbI3-xClx/spiro-OMeTAD/Au configuration. We report normal (NH) and inverted hysteresis (IH) in the J-V characteristics occurring for the same device structure, and the behavior strictly depends on the prepoling bias. NH typically appears at prepoling biases larger than the open circuit bias, while pronounced IH occurs for negative bias prepoling. The transition from NH to IH is marked by an intermediate mixed hysteresis behavior characterized by a crossing point in the J-V characteristics. The measured J-V characteristics are explained quantitatively by the dynamic electrical model. Furthermore, the influence of the bias scan rate on the NH/IH hysteresis is discussed based on the time evolution of the accumulated ionic and electronic polarization charge at the interfaces. Introducing a three-step measurement protocol, which includes stabilization, prepoling, and measurement, we put forward the difficulties and possible solutions for a correct photoconversion efficiency evaluation.
28. Characterization of TiNi shape memory alloys obtained by spark plasma sintering process
Authors: Cirstea, CD; Tolea, F; Leonat, L; Lungu, M; Cucos, A; Cirstea, V; Tsakiris, V

Published: SEP-OCT 2016, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 18, 862, DOI:

This paper presents the research results on the thermal behavior of the 48.5% at Ti-Ni alloys, obtained by spark plasma sintering in vacuum under a pressure of 50 MPa, at temperatures of 850 degrees C and 900 degrees C and holding time of 5 minutes, and subsequently aged in argon for up to 30 minutes at 450 degrees C. Differential scanning calorimetry, dynamic mechanical and dilatometry analysis were used to characterize the transformation properties of the TiNi samples. All the results of differential scanning calorimetry and dynamic mechanical analysis confirmed the hypothesis that the stress-free thermally induced martensitic transformation exists in the investigated TiNi alloys. Annealing at lower temperatures (450 degrees C) in Ni-rich TiNi alloys led to precipitation process which facilitates the formation of the R-phase due to internal stress contributed by precipitates.
29. Shape Memory NiTi Alloys Obtained by Powder Metallurgy Route
Authors: Lucaci, M; Valeanu, M; Orban, RL; Tsakiris, V; Cirstea, DC; Leonat, L

Published: 2011, RESEARCHES IN POWDER METALLURGY, 672, +, DOI: 10.4028/www.scientific.net/MSF.672.99

The effect of Fe, respective Cu, additions as substitute for Ni in NiTi shape memory alloys (SMAs) on the delaying of its phase transition and narrowing hysteresis are well known, NiTi-Fe and NiTi-Cu SMAs having applications especially to the actuators that require such properties. These SMAs are currently produced by conventional melting methods, which are energo-intensive and impose very severe processing conditions to avoid contamination. The results of researches presented in this paper prove the possibility of these SMAs obtaining by powder metallurgy via reactive sintering - more advantageous from both technical and economic point of view. A beneficial effect on both sintering and homogeneity of the obtained SMAs proved to have a controlled mechanical alloying applied to powder mixture before compacting and sintering.
30. Martensitic transformation of Ti50Ni30Cu20 alloy prepared by powder metallurgy
Authors: Valeanu, M; Lucaci, M; Crisan, AD; Sofronie, M; Leonat, L; Kuncser, V

Published: MAR 31 2011, JOURNAL OF ALLOYS AND COMPOUNDS, 509, 4498, DOI: 10.1016/j.jallcom.2011.01.154

Phase transformation behavior of Ti50Ni30Cu20 shape memory alloys prepared by powder metallurgy is analyzed with respect to the duration of mechanical alloying. The processed blends were studied by differential scanning calorimetry and room temperature X-ray diffraction. The martensitic transformations evidenced by thermal scans are discussed in correlation with the relative phase content obtained from the refinement of the X-ray diffraction patterns. (c) 2011 Elsevier B.V. All rights reserved.
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