National Institute Of Materials Physics - Romania

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838 articles found

831. THE EFFECT OF URANIUM DOPING AND SINTERING ATMOSPHERE ON SOME PROPERTIES OF BARIUM-TITANATE CERAMICS

Authors: TANASOIU, C; NICULESCU, H; NICOLAU, P; CUTURICU, A; MICLEA, C; VARZARU, E

Published: 1982, REVUE ROUMAINE DE PHYSIQUE, 27, +, DOI:

832.

Authors: Popa, A; Ilia, G; Pascariu, A; Iliescu, S; Plesu, N

Published: 13 0, , DOI:

833. MICROSTRUCTURE, MAGNETIC AND MAGNETOSTRICTIVE BEHAVIOUR IN RAPIDLY QUENCHED OFF-STOICHIOMETRIC Ni-Mn-Ga FERROMAGNETIC SHAPE MEMORY ALLOYS

Authors: Sofronie, M; Tolea, F; Enculescu, M; Pasuk, I; Popescu, B

Published: , ROMANIAN REPORTS IN PHYSICS, 2022, DOI: 503

This work reports the effect of the rapid solidification technique and thermal treatment on the martensitic transformation (MT), magnetic and magnetostrictive properties on the off-stoichiometric Ni49Mn31Ga20 and Ni51Mn28Ga21 ferromagnetic shape memory ribbons. The samples were investigated by X-ray diffraction, differential scanning calorimetry, scanning electron microscopy, magnetic and magnetostrictive measurements. The temperature dependence of the X-ray phases analysis shows the presence of martensite structures, both tetragonal and monoclinic, at room temperature and allowed to study their evolution through MT. The thermal treatment induces changes in the microstructure with implications in MT and Curie temperatures evolution. The competition between the magnetization orientation and twin boundary motion within martensitic variants under magnetic field evidenced in the magnetic-strain curves was discussed and correlated with the magnetic data.

834. The Role of Interface Defect States in n- and p-Type Ge Metal-Ferroelectric-Semiconductor Structures with Hf0.5Zr0.5O2 Ferroelectric

Authors: Boni, GA; Istrate, CM; Zacharaki, C; Tsipas, P; Chaitoglou, S; Evangelou, EK; Dimoulas, A; Pintilie, I; Pintilie, L

Published: , PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE, 2000500, DOI: 10.1002/pssa.202000500

The discovery of ferroelectricity in doped HfO2 represents an excellent opportunity to overcome the obstacles in manufacturing reliable ferroelectric field effect transistors (FeFET) for nonvolatile memory applications, considering that HfO2 is compatible with Si and Ge and it is already used in semiconductor industry. The presence of interface defects may have detrimental effects on the operation of FeFETs, so their role is systematically investigated in this study in correlation with the substrate doping. Metal-ferroelectric-semiconductor (MFS) structures are fabricated by depositing Hf0.5Zr0.5O2 (HZO) layers on n-type Ge substrate. Their electric properties are compared with those of MFS structures obtained by depositing HZO on p-type Ge, to study the influence of the doping. It is found that, although the ferroelectric properties of HZO are similar, the capacitance and impedance of the MFS structures behave differently. For n-Ge, the occupation probability of a large number of low-lying interface defect acceptor states, charges the interface negatively which adversely affects the C-V response of the MFS, albeit without harming the ferroelectric (P-V) hysteresis. Although the interface defects do not harm ferroelectricity, they could inhibit inversion in p-type Ge or accumulation in n-type Ge so they should be taken into account when designing Ge FeFET devices.

835. Role of vanadium oxide on the lithium silicate glass structure and properties

Authors: Gaddam, A; Allu, AR; Fernandes, HR; Stan, GE; Negrila, CC; Jamale, AP; Mear, FO; Montagne, L; Ferreira, JMF

Published: , JOURNAL OF THE AMERICAN CERAMIC SOCIETY, DOI: 10.1111/jace.17671

The structural role of V in 28Li(2)O-72SiO(2) (in mol%) lithium silicate glass doped with 0.5 mol% V2O5 was assessed using Si-29 and V-51 Nuclear Magnetic Resonance (NMR), Fourier-transform infrared (FTIR), and X-ray photoelectron (XPS) spectroscopy techniques. Despite the low amount of V2O5 used, the structural information obtained or deduced from the statistical analysis of the NMR data could explain the evolution of glass properties after V2O5 addition. The XPS results indicated that all vanadium exists in 5+ oxidation state. Both the Si-29 NMR and FTIR data point toward an increase in the polymerization of the silicate network, caused by the V2O5 acting as network former, capable to form various QVn tetrahedral units (for n = 0, 1, and 2) in the glasses. These QVn units, which are similar to phosphate units, scavenge the Li+ ions and cause the silicate network to polymerize. However, in an overall balance, the entire glass network is depolymerized due to the additional nonbridging oxygens contributed by the vanadium polyhedra. The addition of vanadium causes the network to expand and increases the ionic conductivity.

836. Multilevel Memristive GeTe Devices

Authors: Velea, A; Dumitru, V; Sava, F; Galca, AC; Mihai, C

Published: , PHYSICA STATUS SOLIDI-RAPID RESEARCH LETTERS, 2000475, DOI: 10.1002/pssr.202000475

Phase-change memories have reached an advanced degree of maturity, although, to be able to meet the increasing storage demand, multilevel capability is needed. A GeTe memristor is obtained in an amorphous state and it is subjected to a specific thermal treatment which initiates the transition toward the crystalline state. It is found that this crystalline state initialization process is highly beneficial for subsequently obtaining a large number of intermediate resistive states between the high and low resistive states. Multiple resistance levels are achieved by operating the devices in both DC sweeps and rectangular pulse modes in the low-voltage subthreshold regime. The conduction is modeled using a space charge limited conduction model, showing three distinct conduction regions in the high resistive state which merge toward a single conduction region as the low resistive state is approached. The obtained memristors can be used as multilevel nonvolatile memories or as synapses in neuromorphic computing.

837. Impact of Iridium Oxide Electrodes on the Ferroelectric Phase of Thin Hf0.5Zr0.5O2 Films

Authors: Mittmann, T; Szyjka, T; Alex, H; Istrate, MC; Lomenzo, PD; Baumgarten, L; Muller, M; Jones, JL; Pintilie, L; Mikolajick, T; Schroeder, U

Published: , PHYSICA STATUS SOLIDI-RAPID RESEARCH LETTERS, 2100012, DOI: 10.1002/pssr.202100012

Thin film metal-ferroelectric-metal capacitors with an equal mixture of hafnium oxide and zirconium oxide as the ferroelectric material are fabricated using iridium oxide as the electrode material. The influence of the oxygen concentration in the electrodes during crystallization anneal on the ferroelectric properties is characterized by electrical, chemical, and structural methods. Forming gas, O-2, and N-2 annealing atmospheres significantly change the ferroelectric performance. The use of oxygen-deficient electrodes improves the stabilization of the ferroelectric orthorhombic phase and reduces the wake-up effect. It is found that oxygen-rich electrodes supply oxygen during anneal and reduce the amount of oxygen vacancies, but the nonferroelectric monoclinic phase is stabilized with a negative impact on the ferroelectric properties.

838. Argon pressure dependent optoelectronic characteristics of amorphous tin oxide thin films obtained by non-reactive RF sputtering process

Authors: Ziani, N; Galca, AC; Belkaid, MS; Stavarache, I

Published: , JOURNAL OF MATERIALS SCIENCE-MATERIALS IN ELECTRONICS, DOI: 10.1007/s10854-021-05861-2

In this work, amorphous tin oxide thin films were deposited by non-reactive radio frequency magnetron sputtering. A ceramic SnO2 target was used, while different working pressures were employed. The target to substrate distance was fixed to 17 cm, and the substrate was not intentionally heated. The properties of SnO2 (thickness, refractive index dispersion, optical band gap, resistivity, free carriers concentration, carriers mobility, carriers majority type and their scattering time) have been inferred from spectroscopic ellipsometry, conventional UV-Vis spectroscopy and specific Hall electrical measurements. Thickness and refractive index are slightly dependent on the deposition conditions, while the optical band gap, free carriers concentration and their mobilities are changing from sample to sample. The evolution of the optical band gap and carriers concentration is correlated to the active defects concentration. Amorphous SnO2 films grown at 0.4 Pa have the lowest resistivity of 0.86 Omega cm, a carrier concentration of 1.05x10(18)cm(-3) Vs. The average optical transmittance in visible spectrum is 76%.