Adaptive dipolar correlation in ferroelectric x(Ba0.7Ca0.3)TiO3−(1−x)Ba(Zr0.2Ti0.8)O3

Abstract

Deriving structure-property relationships for multicomponent ferroelectric materials has always been a challenging problem because the properties are mostly driven by subtle nanoscale correlations which are hard to detect. Here we have studied the famous Pb-free material x(Ba_0.7Ca_0.3)TiO₃−(1−x)Ba(Zr_0.2Ti_0.8)O₃(x BCT−BZT) which has been at the center of attention for approximately the last 10 years because of its unprecedented piezoelectric properties. However, the structure-property relationship for x BCT -BZT remains elusive as neither the common concepts nor the experimental results lead to satisfactory models which can fully explain its unusual piezoelectric properties as a function of composition as well as recognize its uniqueness compared to other similar systems. Hence we have applied total neutron-scattering and Raman-scattering methods to examine the local structural correlations of x BCT -BZT in the range 0.40 ≤ x ≤ 0.60 at ambient conditions. By refining large-box atomistic models against the neutron pair distribution functions, we have observed an emerging coherence in the polar displacements of the cations at x = 0.50 , leading to an increased structural ergodicity at the key orthorhombic-tetragonal phase boundary. Given the very similar level of local structural disorder and spontaneous polarization found in the system with x , we propose that the abrupt amplification of piezoelectric properties in this material at a region of phase instability is a consequence of enhanced collaboration amongst the all cations in a strain-reduced local environment. It also indicates that the popular structure-property concept entailing a low-symmetry crystal structure cannot be a generic concept or a precondition.