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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)(Bi0.5Na0.3K0.2)TiO3–xSrTiO3–0.05(Ba0.8Ca0.2) 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 (Td) 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 (Ec ~ 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.

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Mahmoud, A.Er., Fangary, M., Nassary, M. et al. Ferroelectric-to-non-ergodic relaxor phase transition of (Bi0.5Na0.3K0.2) TiO3– (Ba0.8Ca0.2) TiO3 lead-free ceramics by SrTiO3 effect. J Mater Sci: Mater Electron 32, 27625–27635 (2021).

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