M. Veera Gajendra Babu

Role of rubidium cation substitution in the A-site of sodium bismuth titanate ceramics

Effect of large ionic radius cation rubidium (Rb) substitution in the A-site of sodium bismuth titanate (Bi0.5Na0.5−xRbx) TiO3 ceramics is studied. Influence of substitution on intrinsic and extrinsic contribution and impact on ferroelectric properties and piezoelectric constant are investigated. Small rhombohedral lattice distortion (δr) and minimum homogeneous strain (δ) are the primary intrinsic parameters which favors the extrinsic parameters such as domain wall motion and mobility of non-180° domain switching. Enhanced mobility softens the coercive field and increases remnant polarization to maximum. Reduced lattice distortion, low strain and enhanced mobility are the significant factors for enhanced piezoelectric constant, highest remnant polarization and decreased coercive field in (Bi0.5Na0.5−xRbx) TiO3 ceramics.

Coexistence of ferroelectric phases and electric field induced structural transformation in sodium potassium bismuth titanate ceramics

Lead-free sodium potassium bismuth titanate (1−x)[Na0.5Bi0.5TiO3]-x[K0.5Bi0.5TiO3] (NKBTx) ceramics have been believed to be a rhombohedral crystal system with R3c symmetry up to x = 0.16 mole fraction, right now. For the first time, on the contrary, we have disclosed the existence of a low-symmetry (MA)-type monoclinic phase (69%) along with rhombohedral R3c (31%) in the NKBT0.10 sample from Rietveld studies on conventional and high-energy synchrotron powder diffraction data in the unpoled state. The peak splitting and reduced FWHM of {110}pc and {111}pc reflections after poling indicate the field-induced structural transformation. Rietveld analysis reveals that the monoclinic (Cc) phase is partially transformed to rhombohedral (R3c) at 50 kV/cm. Two distinct dielectric anomalies are noticed in the dielectric curve at 120 and 310 °C corresponding to freezing temperature (Tf) and glass-like transition temperature (Tm), respectively. The dielectric diffusivity (γ) estimated from the modified Curie-Weiss la...

A correlation between structural distortion and variation of TC in Ba1−x/2LaxBi4−x/2Ti4O15

Ba and Bi ions were simultaneously substituted by La ion up to 0.3 mole fraction and studied by powder XRD and temperature dependent dielectric measurements. Perovskite slab thickness reduces due to octahedral tilting and the cell volume decreases. Low mole fraction of simultaneous substitution of La is preferred as it increases physical properties.