The structural, electrical, optical and thermoelectric characteristics of the Pb-free Cs2BiCuBr6 and Cs2BiCuI6 double perovskites are examined in this work using first-principles density functional theory (DFT). Both compounds are established to be structurally stable and exhibit semiconducting character with narrow bandgaps significantly influenced by spin-orbit coupling (SOC) effects due to presence of the heavy Bi atoms. Optical analysis reveals that Cs2BiCuBr6 and Cs2BiCuI6 possess superior visible-light absorption, higher dielectric response, and stronger optical conductivity, making it a promising candidate for optoelectronic devices. Thermoelectric analysis shows that Cs2BiCuI6 offers enhanced performance at high temperatures, while Cs2BiCuBr6 is more effective at room temperature due to its lower thermal conductivity. Cs2BiCuBr6 and Cs2BiCuI6 support flexible doping strategies for indirect bandgap semiconducting (p-type and n-type) applications.
The glass transition and crystallization behavior of Ge17.5As15Se52.5S15 chalcogenide glass were analyzed by differential scanning calorimetry (DSC) under various heating and cooling rates ranging from 10 to 25 K/min. It was observed that both the glass transition temperature (T g) and the peak crystallization temperature (T p) systematically increase with increasing rate. The activation energy associated with the glass transition (E g approximate to 250.5 kJ/mol) was evaluated using the Moynihan approach, whereas the crystallization activation energy (E c approximate to 205.2 kJ/mol) was determined based on the Kissinger method. The calculated fragility index (m approximate to 28) suggests that the studied glass behaves as a relatively strong system. Overall, the obtained results indicate a stable thermal response and a notable resistance to crystallization, offering valuable insight into the kinetic and structural features of Ge-As-Se-S chalcogenide glass systems.
The values of thirteen elastic constants C 11, C 12, C 13, C 15, C 22, C 23, C 25, C 33, C 44, C 46, C 35, C 55, and C 66 for compounds TlFeS2 and TlFeSe2 have been calculated from first principles, and the bulk moduli of elasticity, shear and Young moduli, and Poisson's ratios have been determined. The values of the Debye temperature and Gr & uuml;neisen parameters of crystals TlFeS2 and TlFeSe2 have been estimated. Propagation velocities of longitudinal and transverse acoustic waves in TlFeS2 crystals and TlFeSe2 in different crystallographic directions, as well as temperature dependences of thermodynamic functions: free energy, phonon part of internal energy, entropy, heat capacity, and thermal conductivity, have been calculated from first principles.
Researches on Ba0.85Ca0.15Zr0.1Ti0.9O3 (BCZT) ceramics in terms of the energy storage applications have shown that their practical applications are limited by their low effective energy storage density (W rec) and energy storage efficiency (eta). To further enhance the effective energy storage density (W rec) and energy storage efficiency (eta) of BCZT ceramics, this work dopes BCZT ceramics with various proportions of Bi(Zn0.5Zr0.5)O3(BZZ) ((1 - x)BCZT-xBZZ). Dense surface microstructure and small grain size of 3.11 mu m are realized for x = 10%. Under breakdown electric field strength (E b) of 100 kV/cm, x = 10% achieve W rec of 0.80 J/cm3 and eta of 84.3%. The ferroelectric performance is enhanced by appropriate BZZ doping amount, which densifies the system, refines grain size and facilitates the system's relaxor behavior. The enhancement in ferroelectric property is beneficial to the realization of miniaturization for the application of ceramic capacitors.
Multiferroic (1 - x)BiFeO3-xPbTiO3 binary ceramics series exhibit interesting features such as tetragonality c/a, polarization, and high Curie temperature. The composition with x = 0.3 possesses a morphotropic phase boundary (a boundary separating rhombohedral and tetragonal phases). This is a very fascinating character of this composition as it exhibits two ferroic orderings which result in the enhancement of the ferroelectric properties of the system. The structural information related to this system is very crucial to predict the ferroelectricity in this compositional series. Goldschmidt's tolerance factor is one of the important aspects to determine the stability of the perovskite (ABO3 type crystal) structure. In the present case, polycrystalline 0.7BiFeO3-0.3Pb1-xSrxTiO3 compositions with x = 0, 0.2, 0.4, 0.6, 0.8, and 1.0, were selected to determine the effect of Sr2+ substitution at the Pb-site in the composition, and the comparative correlation studies were conducted for ferroelectric ordering in the system.
