Structural, morphological, optical and electrical properties of yttrium-doped calcium strontium titanate prepared by solid-state reaction technique

Fine ceramics of calcium strontium titanate and yttrium-doped calcium strontium titanate having formula (YxCa0.50-xSr0.50)TiO3 where x = 0.0, 0.05, 0.10 and 0.15 have been prepared by using a solid-state reaction technique. Thermal analysis using thermogravimetric analysis and differential thermal analysis of the prepared material has been performed to determine the calcination temperature. Formation of desired well-crystalline material belonging to orthorhombic phase with space group as 'Pnma' was confirmed by using powder X-ray diffraction analysis. Surface morphology has been studied by scanning electron microscopy which shows the formation of irregular features with an average grain size lying in the range of 0.58 to 0.84 mu m. The elemental composition of the prepared material was studied by using energy-dispersive X-ray analysis which shows the presence of all the major elements present in the prepared compositions. Ultraviolet-visible spectroscopic studies show that the bandgap of the prepared material lies in the range of 3.5 to 3.7 eV. Fourier transform infrared spectra show the presence of Ti-O stretching and Ti-O-Ti bending modes of vibration in the prepared material. The FT-Raman spectroscopy shows the presence of orthorhombic perovskite active modes such as Ca-TiO3 lattice mode, Ti-O-3 torsional mode, O-Ti-O bending and Ti-O symmetric stretching vibrations. The dielectric constant (epsilon') with respect to frequency shows the contribution of electronic, ionic, dipolar and surface polarization for the high value of epsilon' at low frequencies, and the temperature dependence of epsilon' shows low-temperature phase transition as well for yttrium-doped calcium strontium titanate. The frequency dependence of ac conductivity follows the Mott relation which shows the increase in ac conductivity with the increase in frequency. Thus, such rare-earth-doped material can be used in the fabrication of high-frequency dielectric devices and microwave devices.