Coexistence of local structural heterogeneities and long-range ferroelectricity in Pb-free (1−x)Ba(Zr0.2Ti0.8)O3−x(Ba0.7Ca0.3)TiO3 ceramics

Environmentally benign\n(1-x)Ba(Ti$_{0.8}$Zr$_{0.2}$)O$_3$-x(Ba$_{0.7}$Ca$_{0.3}$)TiO$_3$ (BZT-BCT)\nceramics are promising materials due to their remarkable high piezoresponse\n[Liu and Ren, Phys. Rev. Lett. \\textbf{103}, 257602 (2009)]. In this Letter, by\nfocusing on local and average structure in combination with macroscopic\nelectromechanical and dielectric measurements we demonstrate the structure\nproperty relationship in the tetragonal BZT-BCT ceramic. During\nhigh-temperature cubic to tetragonal phase transformation, polar nanoregions\nare manifested through the spontaneous volume ferroelectrostriction at\ntemperatures below $\\sim$ 477 K. Temperature-dependent local structural\ninvestigations across the Zr K edge extended x-ray absorption fine structure\nspectroscopy reveal an anomalous collaboration between the ZrO$_{6}$ and\nTiO$_6$ octahedra. These octahedra compromise their individuality during\npolarization development. The presence of domains of submicron size embedded\ninside the macroscopic ferroelectric regions below T$_{m}$, as well as their\nhierarchical arrangement, is observed by piezo-response force microscopy.\nEffects of the existence of the structural/polar heterogeneities below T$_{m}$\nare observed also when polarizibilities of the poled and the unpoled samples\nare compared; the poled sample is found to be more susceptible to the electric\nfield. In addition, by using electric field dependent x-ray diffraction studies\nwe also show that this ceramic under field exhibits reduction of tetragonal\ndistortion, which is consistent with earlier reports.\n