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