Disorder-induced structural, ferroelectric, piezoelectric, and optical properties variation in Hf substituted BT

The effect of substitution of Hf on the structural, dielectric, ferroelectric, piezoelectric, and optical behavior of BT has been studied in this work. Hf lies below Zr in the same group of the periodic table, so better performance is expected from Hf substituted BT. XRD analysis revealed the formation of the tetragonal phase for BT, orthorhombic phase for BHT-3 and BHT-5, and rhombohedral phase for BHT-8. The Raman spectroscopy confirmed the presence of two types of octahedra i.e., [TiO₆] and [HfO₆] in Hf doped BT. The average grain size increased linearly for Hf substituted BT except for BHT-5. The dielectric constant was maximum for BHT-3. The TT-C (tetragonal-cubic) temperature decreased whereas the TO-T (orthorhombictetragonal) temperature increased with an increase in Hf content in BT. The maximum value of remanent polarization and piezoelectric charge coefficient has been found for BHT-5. The absorbance vs. wavelength plot showed the signature of the d-d transition present in all the compositions. The direct band gap increased with increasing Hf content in BT but is lower than previously reported values. Hf substitution stabilizes the phase transition near room temperature and increases the d33 value more than pure BT. (author)