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(Ni_1/2Hf_1/2)O₃-(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 (d₃₃ = 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 ∼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.