Ferroelectric-to-non-ergodic relaxor phase transition of (Bi0.5Na0.3K0.2) TiO3– (Ba0.8Ca0.2) TiO3 lead-free ceramics by SrTiO3 effect

In this work, a series compositions of [(0.95?x)(Bi_0.5Na_0.3K_0.2)TiO₃–xSrTiO₃–0.05(Ba_0.8Ca_0.2) TiO₃] Pb-free ceramics (0.0?≤?x?≤?0.2) abbreviation (BKNT–ST–BCT) were synthesized by conventional sintering method. Effect of ST addition on the crystal structure, domain structure, dielectric and ferroelectric properties were investigated. The crystal structure was monitored by XRD and the patterns shown phase crossover from tetragonal to pseudo-cubic caused by lower crystal symmetry of lattice effect at high content of ST. Morphology of sintered ceramics were characterized by SEM, while the domain structure of ST?=?0.0 at different temperatures was examined by In situ TEM. Diffused phase transition corresponding to ferroelectric to ergodic relaxor at lower T has been observed at depolarization temperature (T_d) at (ST < 0.15), while the permittivity peak which detected at ST?=?0.2 in whole range of temperature denote non-ergodic relaxor to paraelectric phase transition. All compositions show normal ferroelectric (P–E) loop at room temperature even ST?=?0.2 with low coercive field (E_c?~?15 kV/cm), while slim relaxor (P–E) loop was observed at (T?=?200 °C). Present normal ferroelectric properties of ST?=?0.2 are attributed to the domain growth and domain wall displacement above the domain switching electric field. All samples belonging to (x?≤?0.1) shown current peak corresponding to ferroelectric phase transition at domain switching field. Samples belonging to (x?≥?0.15) shown two nominal peaks where the second peak is corresponding to ferroelectric-to-another ferroelectric phase transition with different crystal symmetry.

     

Influence of Se on the electron mobility in thermal evaporated Bi2(Te1−xSex)3 thin films

Thermoelectric solid solutions of Bi₂ (Te_1−xSe_x)₃ with x = 0, 0.2, 0.4, 0.6, 0.8 and 1 were grown using the Bridgman technique. Thin films of these materials of different compositions were prepared by conventional thermal evaporation of the prepared bulk materials. The temperature dependence of the electrical conductivity σ, free carriers concentration n, mobility μ_H, and seebeck coefficient S, of the as-deposited and films annealed at different temperatures, have been studied at temperature ranging from 300 to 500 K. The temperature dependence of σ revealed an intrinsic conduction mechanism above 400 K, while for temperatures less than 400 K an extrinsic conduction is dominant.The activation energy, ΔE, and the energy gap, E_g, were found to increase with increasing Se content. The variation of S with temperature revealed that the samples with different compositions x are degenerate semiconductors with n-type conduction. Both, the annealing and composition effects on Hall constant, R_H, density of electron carriers, n, Hall mobility, μ_H, and the effective mass, m^∗/m₀ are studied in the above temperature range.     

Transport Properties of Bi_2S_3 Single Crystals

Bi2S3 single crystals were grown by using a modification of Bridgman method. Measurements of the electrical conductivity, Hall effect and thermoelectric power （TEP） were preformed in two crystallographic directions （parallel and perpendicular to the c-axis）. The measurements showed that the electrical conductivity, Hall mobility, and Seebeck coefficient have anisotropic nature. From these measurements some physical parameters were estimated and the crystals showed n-type of conduction mechanism. Also, values of the energy gap were found to be different in the two directions.     

Growth and transport properties of AgInS2 ternary semiconductor

Journal of Materials Science: Materials in Electronics - A technique based on the Bridgman method was used to make single crystals of AgInS2. X-ray diffraction was used to determine the crystal...