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Lead halide perovskites have drawn considerable attention on account of their potential applications in solar cell and optoelectronic devices. To realize such technological possibilities, the optical characterizations of these materials must be assessed. This paper presents a comprehensive study of the temperaturedependent optical properties of CH 3 NH 3 PbBr 3 single crystals between 4.5 and 400 K within an energy range of 0.73 to 6.42 eV determined through spectroscopic ellipsometry. The profile of the room-temperature refractive index was typical of a semiconductor and decreased markedly with an increase in temperature with thermo-optic coefficients of approximately −4.18 × 10 −4 and −3.29 × 10 −4 K −1 at 600 and 1200 nm, respectively. The cooling− heating cycles of the extinction coefficient reflected the thermal hysteresis of the first-order orthorhombic−tetragonal structural phase transition. Moreover, the Urbach energy, fundamental band gap, exciton peak position, exciton binding energy, and interband transition energies were considerably affected during the structural phase transitions of orthorhombic−tetragonal I at 130 K, tetragonal I−tetragonal II at 150 K, and tetragonal II−cubic at 240 K. These results provide crucial information for the design and fabrication of lead halide perovskite-based devices at various temperatures.

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The modification of the structure lanthanum orthoferrites (LaFeO 3 Þ to obtain ceramic materials with enhanced structural, optical, and electrical properties constitutes an active area of research. The preparation of La 0:8 Pb 0:2 (Fe, Ti) 0:5 O 3 (LPFTO) ceramic nanoparticles by following a cation substitution approach from LaFeO 3 using sol-gel and sintering methods is described. The electrical and dielectric properties of the obtained material are investigated. The contribution of grain and grain boundary in the conduction mechanism is demonstrated by complex impedance analysis. The LPFTO ceramic nanoparticles exhibit a giant dielectric constant of the order of 10 8 . The conductivity analysis suggests the occurrence of thermally activated semiconductor behavior. Moreover, the ferromagnetic-paramagnetic semiconductor transition temperature is observed at 385 K. The ac conductivity behavior satisfies the nonoverlapping small-polaron tunneling (NSPT) model.

This study aims to investigate the electrical polarization of Ba1-xSrxTiO3 (x = 0.0, 0.2, 0.6, and 0.8) perovskite materials. The materials were synthesized using mechano-synthesis. The structural behaviour was assessed using X-ray diffractometer (XRD), revealing that all samples have a tetragonal perovskite structure with a lattice parameter that decreases with an increase in Sr. The electrical polarization was investigated using an electrometer, showing decreasing spontaneous and saturation polarizations as more Sr is substituted into the Ba sites of (Ba,Sr)TiO3. The decreasing lattice parameters and spontaneous and saturation polarizations in these materials indicate that the crystal structure changes from tetragonal to cubic as more Sr is added.

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