P Murugavel

The electrical poling of piezoceramics is an essential process, to maximize their piezocoefficient prior to applications, which can significantly alter their other physical properties. In this study, the effect of poling on the properties of lead free 0.5Ba(Zr0.2Ti0.8)O3-0.5(Ba0.7Ca0.3)TiO3 exhibiting large piezocoefficient was investigated. The sample revealed octahedral distortion induced structural transformation upon poling. The impedance spectrum displayed the resonance modes in poled state, where maximum power transmission is feasible. The polarization hysteresis loop exhibited an asymmetry with an internal bias electric field of 41 V/mm due to the field induced orientational defect. The strain measurements revealed 50% enhancement in electrostriction for the sample after poling. Additionally, the sample revealed an incremental change in bandgap due to B-site cationic off-centre displacements induced by the octahedral distortion. Importantly, the poling induced large internal bias field and the near UV bandgap of the sample facilitated the observed large photovoltaic response with giant open circuit voltage of 18 V which could open up an additional application in the fields such as photovoltaic and UV detector for this versatile compound.

Lead-free, high piezocoefficient 0.5Ba(Zr0.2Ti0.8)O3-0.5(Ba0.7Ca0.3)TiO3 film is fabricated on soft magnetic Ni foil as a substrate using a pulse laser deposition technique for the magnetoelectric studies. The x-ray diffraction analysis confirms the phase pure formation of polycrystalline ferroelectric film along with the presence of NiO formed during the high temperature growth process. The obtained lattice parameters suggest that the native oxide could favour the coherent growth of a ferroelectric layer. The film exhibits ferroelectric characteristics with a polarization value of 23 μC cm-2 at 225 kV cm-1. The fabricated heterostructure displayed a high magnetoelectric coupling coefficient with the maximum magnetoelectric voltage coefficient (α 31) value of 1.08 V cm-1 Oe-1 at low field of 44 Oe. It is noteworthy to mention that the observed α 31 is comparable to the earlier reported toxic lead-based similar systems. The comparison between the experimental and calculated α 31 values suggests that the strain transfer percentage efficiency is around 69%, which is responsible for the observed large ME coupling. These experimental findings give a way to achieve high magnetoelectric coefficients by fabricating the oxide piezoelectric layer directly on the clamping free magnetic substrate.