National Institute Of Materials Physics - Romania

Antiferroelectric random access memory (AFERAM) is one of the newest alternative non-volatile memory technologies to emerge in recent years. ZrO2-based antiferroelectric films are exceptionally well-suited for memory applications with very high cycling endurance (>10(10)) and low operating voltages (< 2 V). Lightly alloying ZrO2 with HfO2 is performed to assess AFERAM device performance with back-end-of-line compatible thin film Zr1-xHfxO2 (x <= 0.13) capacitors. The transition fields associated with antiferroelectric behavior are reduced with more Hf incorporation, yielding a larger magnitude switching polarization and memory window. Cycling endurance beyond 10(10) cycles is conducted on thin film capacitors where wake-up in AFERAM first leads to an increase, then a decrease in the memory window at a cumulative cycle number found to be dependent on the amount of Hf-incorporation. Hf-incorporation into ZrO2 is demonstrated to be a feasible way to improve the memory window in ZrO2-based AFERAM.

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.

The manipulation of magnetic anisotropy represents the fundamental prerequisite for the application of magnetic materials. Here we present the vectorial magnetic properties of nanostructured systems and thin films of Fe and FeCo prepared on linearly trenched Mo templates with thermally controlled periodicity. The magnetic properties of the nanosystems are engineered by tuning the shape, size, thickness, and composition parameters of the thin films. Thus, we control coercivity, magnetization, orientation of the easy axis of magnetization, and the long-range magnetic order of the system in the function of the temperature. We distinguish magnetic components that emerge from the complex morpho-structural features of the undulating Fe or FeCo nanostructured films on trenched Mo templates: (i) assembly of magnetic nanowires and (ii) assembly of magnetic islands/clusters. Uniaxial anisotropy at room temperature was proven, characterized, and explained in the case of all systems. Our work contributes to the understanding of magnetic properties necessary for possible further applications of linear systems and undulated thin films.

A deeper understanding of the coupling at the interface of multiferroics heterostructures is being achieved by the use of synchrotron radiation techniques. Here, the authors use k-resolved soft X-ray photoemission spectroscopy and first principles calculations to investigate the band structure of several multiferroic heterostructures, isolating the distinct signature of the interface. Physics of the multiferroic interfaces is currently understood mostly within a phenomenological framework based on screening of the polarization field and depolarizing charges. Additional effects still unexplored are the band dependence of the interfacial charge modulation and the associated changes of the electron-phonon interaction, coupling the charge and lattice degrees of freedom. Here, multiferroic heterostructures of the colossal-magnetoresistance manganite La1-xSrxMnO3 buried under ferroelectric BaTiO3 and PbZrxTi1-xO3 are investigated using soft-X-ray angle-resolved photoemission. The experimental band dispersions from the buried La1-xSrxMnO3 identify coexisting two-dimensional hole and three-dimensional electron charge carriers. The ferroelectric polarization modulates their charge density, affecting the coupling of the 2D holes and 3D electrons with the lattice which forms large Frohlich polarons inherently reducing mobility of the charge carriers. Our k-resolved results on the orbital occupancy, band filling and electron-lattice interaction in multiferroic oxide heterostructures modulated by the ferroelectric polarization disclose most fundamental physics of these systems needed for further progress of beyond-CMOS ferro-functional electronics.

In the present work, new luminescent lanthanide complexes with extended mesomorphic range were prepared by coordination to lanthanide ions (Eu3+, Sm3+ and Tb3+) of the new 4-pyridone based organic ligands (L) with 3,4-(7-n) and 3,5-di(alkyloxy)benzyl (8-n) mesogenic groups and variable length (n = 12 or 14 carbon atoms) onto the benzyl unit. The cumulative results of the elemental analyses as well as the H-1, C-13 NMR and IR spectroscopies support the structure of the organic derivatives and their lanthanide complexes [LnL(3)(NO3)(3)] (9-n/Ln and 10-n/Ln) described in this work. These complexes show characteristic lanthanide solid state emission, both at room and elevated temperatures corresponding to crystalline, glassy or liquid crystal states. The long range SmA phases displayed by all complexes were supported by a combination of characterization methods, including: differential scanning calorimetry (DSC), polarizing optical microscopy (POM) and variable-temperature powder X-ray diffraction (XRD). This work shows that the number, substitution pattern and length of flexible alkoxy chains are important parameters to control the phase-transition characteristics of the lanthanide complexes. Complexes with 3,4-disubstituted pattern (9-n/Ln) show higher clearing temperatures (nearly 60 degrees C for Eu3+, 70 degrees C for Sm3+ and 85 degrees C for Tb3+ complexes) compared to their counterparts with 3,5-disubstituted pattern (10-n/Ln). Moreover, complexes 9-n/Ln crystallize when cooling their LC phase while complexes 10-n/Ln are stable in glassy state at room temperature as a consequence of the different close interdigitated molecular packing evidenced by XRD measurements. Dielectric spectroscopy was employed to detect the changes of order degree specific to each phases (crystalline, LC or isotropic). The variation of dielectric constant and the electrical conductivity versus temperature shows three transition intervals for selected complexes 10-14/Sm and 10-14/Tb, which delimit the main intervals: 45-60 degrees C, 90-110 degrees C; 140-160 degrees C corresponding to the Cr-1-Cr-2, Cr-2 - SmA and SmA-Iso transitions, and agree very well with the DSC results. The change of characteristic time, obtained by Havriliak-Negami fit function, with temperature also provides a very good correlation with the DSC and POM results. (C) 2022 Elsevier B.V. All rights reserved.

As ferroelectric Hf0.5Zr0.5O2 (HZO) thickness scales below 10 nm, the switching characteristics are severely distorted typically showing an antiferroelectric-like behavior (pinched hysteresis) with reduced remanent polarization. Using Landau-Ginsburg-Devonshire (LGD) theory for the analysis of the experimental results, it is shown here that, in thin (5 nm) HZO, depolarization fields drive the system in a stable paraelectric phase coexisting with a metastable ferroelectric one, which explains the pinched hysteresis. This state of matter resembles a first order ferroelectric above the Curie temperature which is known to result in similar double-loop behavior. Here, based on the analysis of experimental data in the framework of LGD theory, it is reported that charge injection and trapping at pre-existing interface defects during field cycling ("wake-up") screens the depolarization field stabilizing ferroelectricity. It is found in particular that a sufficiently large energy density of interface states is beneficial for the recovery of fully open ferroelectric loops. HfO2-based ferroelectric materials have immense technological potential and so significant attention has been given to improve the ferroelectric properties at low-thickness. Here, using Landau Devonshire theory, the authors show the origin of pinched hysteresis loops is connected with the existence of pronounced depolarizing fields which are minimized during field cycling recovering the full ferroelectric loops.

Tunable blue-white-orange emitting LaPO4:Ce3+/Mn2+/Zr4+(LPCMZ) phosphors have been synthesized by co precipitation followed by calcination. The X-ray diffraction (XRD) shows the phase transition from hexagonal to monoclinic between 600 and 700 ?C, accompanied by the increase of average nanocrystallites size from 8 to 64 nm. The Raman measurements revealed the vibrational modes associated with the LPCMZ crystalline phases, where the band positions and the full width at half maximum values depend on the structural parameters and nanocrystals size. For low-temperature calcination of 500 ?C, scanning electron microscopy (SEM) revealed nanoclusters composed of thinner nanoneedles, which developed into a rod-like self-assembly shape for higher calcination temperatures at around 900 ?C. Electron paramagnetic resonance (EPR) spectroscopy reveals a broad isotropic EPR signal, assigned to agglomerated/clustered Mn2+ ions, which are dispersed only at high temperatures above 900 ?C. The photoluminescence spectra recorded under UV-excitation of Ce3+ ions showed the Mn2+ green/red (546, 630 nm) emissions due to an energy transfer (ET) between Ce3+ and Mn2+. Depending on the calcination temperature, the Mn2+ emission color can be finely adjusted from blue to white and orange.

The incorporation of therapeutic-capable ions into bioactive glasses (BGs), either based on silica (SBGs) or phosphate (PBGs), is currently envisaged as a proficient path for facilitating bone regeneration. In conjunction with this view, the single and complementary structural and bio-functional roles of CuO and Ga2O3 (in the 2-5 mol% range) were assessed, by deriving a series of SBG and PBG formulations starting from the parent glass systems, FastOs (R) BG -38.5SiO2-36.1CaO-5.6P2O5-19.2MgO-0.6CaF2, and 50.0P2O5-35.0CaO-10.0Na2O-5.0 Fe2O3 (mol%), respectively, using the process of melt-quenching. The inter-linked physico-chemistry -biological response of BGs was assessed in search of bio-functional triggers. Further light was shed on the structural role -as network former or modifier -of Cu and Ga, immersed in SBG and PBG matrices. The preliminary biological performance was surveyed in vitro by quantification of Cu and Ga ion release under homeostatic conditions, cytocompatibility assays (in fibroblast cell cultures) and antibacterial tests (against Staphylococcus aureus). The similar (Cu) and dissimilar (Ga) structural roles in the SBG and PBG vitreous networks governed their release. Namely, Cu ions were leached in similar concentrations (ranging from 10-35 ppm and 50-110 ppm at BG doses of 5 and 50 mg/mL, respectively) for both type of BGs, while the release of Ga ions was 1-2 orders of magnitude lower in the case of SBGs (i.e., 0.2-6 ppm) compared to PBGs (i.e., 9-135 ppm). This was attributed to the network modifier role of Cu in both types of BGs, and conversely, to the network former (SBGs) and network modifier (PBGs) roles of Ga. All glasses were cytocompatible at a dose of 5 mg/mL, while at the same concentration the antimicrobial efficiency was found to be accentuated by the coupled release of Cu and Ga ions from SBG. By collective assessment, the most prominent candidate material for the further development of implant coatings and bone graft substitutes was delineated as the 38.5SiO2-34.1CaO-5.6P2O5-16.2MgO-0.6CaF2-2.0CuO-3.0Ga2O3 (mol%) SBG system, which yiel-ded moderate Cu and Ga ion release, excellent cytocompatibility and marked antibacterial efficacy. (c) 2021 The Chinese Ceramic Society. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

The consumer market requests infrared (IR) optical components, made of relatively abundant and environmentally friendly materials, to be integrated or attached to smartphones. For this purpose, three new chalcogenides samples, namely Ge23.3Zn30.0Se46.7 (d_GZSe-1), Ge26.7Zn20.0Se53.3 (d_GZSe-2) and Ba4.0Ge12.0Zn17.0Se59.0I8.0 (d_GZSe-3) were obtained by mechanical alloying and processed by spark plasma sintering into dense bulk disks. Obtaining a completely amorphous and homogeneous material proved to be difficult. d_GZSe-2 and d_GZSe-3 are glass-ceramics with the amount of the amorphous phase being 19.7 and 51.4 wt. %, while d_GZSe-1 is fully polycrystalline. Doping with barium and iodine preserves the amorphous phase formed by milling and lowers the sintering temperature from 350 degrees C to 200 degrees C. The main crystalline phase in all of the prepared samples is cubic ZnSe or cubic Zn0.5Ge0.25Se, while in d_GZSe-3 the amorphous phase contains GeSe4 clusters. The color of the first two sintered samples is black (the band gap values are 0.42 and 0.79 eV), while d_GZSe-3 is red (E-g is 1.37 eV) and is transparent in IR domain. These results are promising for future research in IR materials and thin films.

Polycrystalline La(0.8)K(0.2-x)Pb(x)MnO3 (x = 0.05, 0.10, 0.15, 0.20) ceramics were successfully prepared by flash combustion route and their structural, morphological, magnetic and magnetocaloric properties were investi-gated. Structural analyses using X-ray diffraction reveal that all samples are crystallized in the rhombohedral structure and belong to R <(3) over bar > c space group. The increase of Pb doping does not modify the crystalline structure but changes the grain size and lattice parameters. X-ray photoelectron spectroscopy (XPS) fitting results of Mn 2p peaks confirmed the coexistence of Mn3+ and Mn4+ ions which contribute to the double exchange interactions improving the ferromagnetic order in the samples. The magnetization's temperature and magnetic field de-pendences indicate a second-order ferromagnetic-paramagnetic transition of the ceramics. A significant mag-netic entropy change near room temperature was observed for La0.8K0.1Pb0.1MnO3, showing considerable magnetocaloric properties. Furthermore, electron paramagnetic resonance spectroscopy (EPR) was also used to examine the ferromagnetic-paramagnetic transition.