  Recent years have witnessed considerable work on the development of lead-free
piezoelectric ceramic materials and their structure-property correlations. The
development of piezo response is a strong function of phase evolution in these
materials. In this work, we report the effect of Ru doping and consequent phase
evolution on maximization of piezoelectric response of polycrystalline
lead-free barium titanate, depicted as Ba(RuxTi1-x)O3 (BRT). The samples were
prepared in a narrow compositional range of using conventional solid-state
reaction method. Ru doping increases the leakage current of BaTiO3 samples
attributed to increased oxygen vacancy concentration due to substitution of
Ti4+ by Ru3+. Detailed structural analysis reveals samples exhibiting
coexistence of tetragonal (space group: P4mm) and orthorhombic (space group:
Amm2) structured phases near the room temperature reveal relatively enhanced
piezoelectric properties. The BRT sample with Ru content of 2 mol% yields a
maximum longitudinal piezoelectric coefficient, d33 of 269 pC/N, a high strain
value of 0.16% with a large remnant polarization of 19 micro C/cm2 and a
coercive field of 5.8 kV/cm. We propose that the 4d orbital of Ruthenium plays
a crucial role in improving the functional properties and in decreasing the
ferroelectric Curie temperature (Tc). Our work provides clues into tailoring
the phase evolution for designing lead-free piezoelectric materials with
enhanced piezoelectric property.
