Raman scattering, microstructural and dielectric studies on Ba1−xCaxBi4Ti4O15 ceramics

Polycrystalline powders of Ba1−xCaxBi4Ti4O15 (where x = 0, 0.25, 0.50, 0.75 and 1) were prepared via the conventional solid-state reaction route. X-ray diffraction (XRD) and Raman scattering techniques have been employed to probe into the structural changes on changing x. XRD analyses confirmed the formation of monophasic bismuth layered structure of all the above compositions with an increase in orthorhombic distortion with increase in x. Raman spectra revealed a redshift in A1g peak and an increase in the B2g/B3g splitting with increasing Ca content. The average grain size was found to increase with increasing x. The temperature of the maximum dielectric constant (Tm) increased linearly with increasing Ca-content whereas the diffuseness of the phase transition was found to decrease with the end member CaBi4Ti4O15 showing a frequency independent sharp phase transition around 1048 K. Ca doping resulted in a decrease in the remnant polarization and an increase in the coercive field. Ba0.75Ca0.25Bi4Ti4O15 ceramics showed an enhanced piezoelectric coefficient d33 of 15 pC N−1 at room temperature. Low values of dielectric losses and tunability of temperature coefficient of dielectric constant (τɛ) in the present solid-solution suggest that these compounds can be of potential use in microwave dielectrics at high temperatures.