Professor Wojciech Kuczynski, a Research Staff Member at the Institute of Molecular Physics of the Polish Academy of Sciences in Poznan, Poland, passed away on 5 December 2020.Professor Kuczynski w...

ABSTRACT The revived multifunctional material Li2Pb2Eu2W2Ti4Ta4O30 (LPEWT) was prepared at high temperature by solution casting technique. The material belongs to the family of tungsten bronze ferroelectrics. The X-ray diffraction pattern of calcined powder done to check the compound formation and it reveals a number of well-defined sharp peaks. The density of the sample found out using common hydrostatic technique is 93% of the theoretical density. The SEM image of the gold plated pellet surface illustrates the grains of different size uniformly distributed throughout the sample with the average grain size of 1.87 μm. The temperature-dependent dielectric study confirms the expected ferroelectric to paraelectric transition . The presence of non-relaxor ferroelectric nature has been verified from both the dielectric and polarization studies. The electrical spectroscopy study reveals conduction mechanism is due to hopping type motion of the charge carriers. Thermistor parameter reveals the usefullness of the material for device fabrication.

ABSTRACT Herein, teh first TEMPprincipal calculations and Monte Carlo Simulation (MCS) were performed to investigate teh magnetic and magneto-caloric properties of PrSi compound. Teh partial magnetic moment of Pr (mPr), and teh exchange interactions parameters (J1, J2) are found to be mPr = 2.8 µB, J1 = 1.707 meV and J2 = 1.312 meV, respectively. Through teh MCS, it was found dat teh Curie temperature value (T c) from ferromagnetic to paramagnetic state is T c = 55 K, which is in good agreement wif teh experimental value which is 54 K. Moreover, it was established dat a slight increase in teh applied magnetic field leads to a high increase in teh magnetic entropy from 4.4 J/kg K for h = 1 T to 13.7J/kg K for h=5 T. Furthermore, teh values of adiabatic temperature change and relative cooling power (RCP) obtained for h = 5 T were found to be 3.6 K and 550 J/kg, respectively.

ABSTRACT We report the synthesis of barium cerium manganite (BaMn0.94Ce0.06O3) single perovskite by using a conventional high-temperature solid-state reaction method. A structural phase transition occurs from hexagonal to orthorhombic confirmed by XRD data analysis after doping cerium (Ce) to the pure barium manganite (BaMnO3) matrix. The average crystallite size of the sample is about 63.38 nm. The lattice strain produced due to the addition of Ce dopant in the host matrix is about 0.00142. The SEM micrograph suggests the average grain size is about 30 μm. It is observed that the grain plays a dominant role compare to grain boundaries in defining the conductivity in the sample. The thermally activated relaxation process is controlled by the immobile charge carriers in the host materials at low-temperature range while controlled by defects at higher temperatures. From all the results, it is confirmed that the sample is dominated by the hopping process. The semicircular Nyquist plots confirm the semiconducting nature of the sample which is well supported by Cole-Cole plots.

ABSTRACT First-principles calculations of density functional theory (DFT) using the generalized gradient approximation (GGA) and generalized gradient approximation with the Hubbard U (GGA + U) for the exchange-correlation energy functional are used to investigate the structural, electronic, and magnetic properties of the spinel system in the range . High-temperature series expansions (HTSE) combined with the Padé approximants (PA) method and mean field theory (MFT) are applied to the systems. The lattice parameter and magnetic moment of Fe and Ni ions increase when Cd content x increases. Density of States (DOS) calculations show that the has a semiconductor behaviour. The obtained theoretical results show that the Curie temperature decreases with x. These obtained results are in agreement with experimental ones.

ABSTRACT Density functional theory (DFT) based full-potential linearized augmented plane wave (FP-LAPW) method approach has been used to investigate the phase stability, pressure-induced phase transition and electronic properties of AlP, AlAs and AlSb compounds. The study has been performed for the zinc blende (B3), rocksalt (B1), wurtzite (B4), NiAs (B8) and CsCl (B2) phases. For structural properties, the Wu-Cohen generalized gradient approximation (WC-GGA) scheme was used while for band structure calculations, in addition to WC-GGA, the modified Becke–Johnson (mBJ) scheme was also used. Results show that the zinc blende phase is most stable amongst the other considered phases. Then the numerical results of the transition pressures have been predicted. The band structure calculations reveal that these compounds adopt a metallic behavior in rocksalt, NiAs and CsCl phases whereas they are semiconductor materials in zinc blende and wurtzite phases.

ABSTRACT Ba(Zr0.2Ti0.8)O3-x(Ba0.7Ca0.3)TiO3 (BZT-xBCT) is a promising lead-free ferroelectric system with high piezoelectricity. Here we carry out phenomenological calculations to explore phase stability and electric field induced phase transition. Study of free energy variation near phase boundaries revealed ultralow energy barrier in single orthorhombic phase region and phase coexistence around inter-ferroelectric transitions. The calculated critical electric field for tetragonal-orthorhombic transition is in reasonable agreement with experimental data. Temperature–composition phase diagram under [001], [011] and [111] oriented electric field are computed, and polarization rotation associated monoclinic structures are studied.

ABSTRACTThe perovskite cesium lead halides have been proposed as promising materials for photovoltaic devices because of their visible light absorption and direct band gap semiconductors. The structural, electronic and optical properties of the bulk CsPbX3 (X = Br, Cl and I) are studied, using density functional theory. In order to use these compounds in photovoltaic applications, the only inconvenient of these materials is that they have a slightly high gap energy value such as: 2.57, 2.16 and 1.88 eV for CsPbCl3, CsPbBr3 and CsPbI3 compounds, respectively. It is known that the efficiency of the solar cells varied with the band gap of the materials used. Moreover, by applying 3% of strain on the perovskite CsPbX3, we have reducing the gap energy value of these materials. The present compounds are one of the promising candidates for photovoltaic applications.

ABSTRACTIn this research paper, a detailed investigation is conducted on the magnetocaloric effect (MCE) properties of the two phases (1−x) La0.6Ca0.4MnO3/(x) La0.6Sr0.4MnO3 composite system by experiments and numerical calculations. The polycrystalline manganites La0.6Ca0.4MnO3 and La0.6Sr0.4MnO3 are synthesized by the citric-gel method. Rietveld refinements of the X-ray diffraction patterns show that both samples are single phase. The Curie temperature Tc is found to be 255 and 365 K for La0.6Ca0.4MnO3 and La0.6Sr0.4MnO3, respectively. The study of the temperature dependence of the magnetic entropy change of (1−x)La0.6Ca0.4MnO3/(x)La0.6Sr0.4MnO3 composite indicates that the optimum composition stands for x = 0.6. Indeed, it gives comparable contributions of two parent compounds, leading to a practically uniform variation of entropy over a wide temperature range. The theoretical modeling of the MCE using Landau theory reveals an acceptable concordance with experimental data indicating the importance of magnetoelastic coupling and electron interaction in the MCE properties of manganite systems.

ABSTRACTThe laser irradiation with band gap light of thermally evaporated As40Se55Bi5 and As40Se45Bi15 thin films was found to be accompanied by structural changes which in turn changed the optical constant. The thin films under investigation were characterized by the X-ray diffraction method to study the structural change and the surface morphology was checked by field emission scanning electron microscope. The composition of the films was verified from the energy dispersive X-ray analysis. The changes in optical properties due to the influence of laser irradiation were calculated from the transmission spectrum recorded by UV–Visible spectrometer in the wavelength region 400–1200 nm. The decrease in optical band gap (photodarkening) is explained on the basis of density of state model proposed by Mott–Davis. The Raman analysis showed the Raman shift and symmetric stretching vibration of As–Se.