Structure characters, and thermal evolution of electrical and elastic behaviors in xBi(Ni_1/2Hf_1/2)O₃-(1-x)PbTiO₃ solid solutions with a tetragonal-pseudocubic phase boundary

In this study, we synthesized solid solutions of xBi(Ni1/2Hf1/2)O-3-(1 - x)PbTiO3 (xBNH-PT) with the aim of elucidating their phase boundary behaviors and the associated physical properties. A tetragonal (T) - pseudocubic (PC) phase boundary was confirmed at x = 0.38. For x = 0.36 and x = 0.37 with distinct tetragonal distortions, a spontaneous ferroelectric-relaxor transition was observed. The introduction of a T-PC phase boundary not only led to enhanced piezoelectric properties (d(33) = 456 pC/N, x = 0.39) but also effectively suppressed the spontaneous ferroelectric-relaxor transition. Detailed analysis revealed that the local structure of the initial state in 0.39BNH-0.61PT remained tetragonal. After poling, a long-range tetragonal phase was formed from the short-range tetragonal clusters, with the c/a value of similar to 1.01. Our observations of frequency dispersion strongly suggest the presence of local inhomogeneities, resulting in distinct poling effects on the dielectric and elastic behaviors of the material.