Structural, morphological, vibrational, and impedance properties of ytterbium modified bismuth titanate

Abstract

Polycrystalline ytterbium modified bismuth titanate Bi4-xYbxTi3O12(x = 0, 0.1, 0.2, and 0.3) solid solutions have been synthesized using a solid state reaction method. The effect of varying the ytterbium content on the structural, morphological, vibrational, and impedance properties of this ceramic have been investigated. According to the experimental results obtained from scanning electron microscopy combined with energy dispersive X-ray analysis, a highly dense grain structure and a randomly oriented plate-like morphology were observed, showing an increase in the material grain size with Yb content. Besides, all the samples were found to be free from any other secondary phase. By means of Raman spectroscopy, it was observed that (Bi2O2)2+ layers remain unaffected with composition variation. These observations prove that Yb3+ substitution for Bi3+ occur predominantly, not only in pseudo-perovskite (Bi2Ti3O12)2- sites, but also in (Bi2O2)2+ layers, leading to cationic disorder and to a decrease in the TiO6 octahedral distortion. Raman measurements show also that all compounds exhibit a perovskite-type orthorhombic structure. This latter result is consistent with Fourier transform infra red analysis, which shows the appearance of two absorption bands below 830 cm−1. The optical band gap obtained from UV–visible spectroscopy has been found to slightly decrease from 3.1 to 3.04 eV with increasing Yb3+ substitution from x = 0 to x = 0.3, respectively. The thermal stability was also investigated. It was found from the differential scanning calorimetry that the Curie temperature (Tc) shifted backwards with increasing Yb content. No significant weight loss was found in the thermo-gravimetric analysis curve up to 800 °C temperature. Besides, the impedance spectroscopy studies show a non-Debye-type relaxation and a relaxation frequency shift to higher side with the increase in temperature. The Nyquist plot shows overlapping semicircles which indicate the existence of both grain and grain boundary effect in the prepared ceramic.