Re‐entrant ferroelectric relaxor phenomena in the (1 − x )[Bi 1/2 (Na 1/2 K 1/2 ) 1/2 TiO 3 ]‐ x PbZrO 3 system

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The solid solution (1 − x )[Bi 1/2 (Na 1/2 K 1/2 ) 1/2 TiO 3 ]‐ x PbZrO 3 , (0.00 ≤ x ≤ 0.12) was investigated to examine the phase equilibria, dielectric and electromechanical properties. The composition corresponding to x = 0.00 exhibits tetragonal symmetry with the expected classical ferroelectric (FE) behavior. The system exhibited FE to relaxor crossover with the addition of lead zirconate at the composition x = 0.05. This is indicated by typical relaxor characteristics such as a transition to the global pseudocubic phase, a constriction in the FE hysteresis loop, and a sudden decrease in the negative strain accompanied by an increase in maximum strain. Most notably, with a further increase in x (>0.05), there is evidence for a return to a FE phase that exhibits classical FE characteristics. The combined results demonstrate that there exists a narrow FE‐relaxor boundary near x = 0.05, where FE and relaxor phases coexist. At the critical composition, enhancement in the piezoelectric properties, including an increase in the effective (350 pm/V) was observed. This transition in the electromechanical properties is consistent with changes observed in the phase equilibria for this solid solution. The crystal structure transitions from tetragonal symmetry for x = 0.00, to pseudocubic symmetry for the relaxor compositions ( x = 0.05), and finally to a lower symmetry perovskite phase for the re‐entrant FE phase ( x > 0.05). This composition‐induced transition from FE to relaxor to a re‐entrant FE state in the (1 − x )[Bi 1/2 (Na 1/2 K 1/2 ) 1/2 TiO 3 ]‐ x PbZrO 3 system is unusual among relaxor FE systems and thus is of great scientific and technological interest.