Structural correlations in the enhancement of ferroelectric property of Sr doped BaTiO₃

The effect of Sr doping in BaTiO₃ (BTO) with nominal compositions Ba_0.80Sr_0.20TiO₃ (BSTO) have been explored on its structural, lattice vibration, dielectric, ferroelectric and electrocaloric properties. The temperature dependent dielectric results elucidate the enhancement in dielectric constant and exhibit three frequency independent transitions around 335, 250 and 185 K, which are related to different structural transitions. All these transitions occur at lower temperature as compared with pristine BTO, however; remnant electric polarization (P _r) of BSTO is much higher than in BTO. The value of P _r is ∼5 μC cm⁻² at room temperature and the maximum P _r ∼ 8 μC cm⁻² is observed at tetragonal to orthorhombic and orthorhombic to rhombohedral transitions. The electro-caloric effect shows the maximum adiabatic change in temperature ΔT ∼ 0.24 K at cubic to tetragonal transition. The temperature dependent synchrotron x-ray diffraction and Raman results show correlations between P _r, crystal structure and lattice vibrations. Our results demonstrate the enhancement in ferroelectric properties of BTO with Sr doping. The origin of the enhancement in ferroelectric property is also discussed in correlations with the appearance of superlattice peak around room temperature due to TiO₆ octahedral distortion. These enhanced properties would be useful to design lead free high quality ferroelectric and piezoelectric materials. (paper)