Análise estrutural e estudo de transição de fase do composto P bxCd(1−x)T iO3: por difração de Raios X e espectroscopia Raman.

Abstract

This work aims to study the structural and phase transition properties of compounds of the type ABO3. This was accomplished with the aid of experimental X-ray diffraction (XRD) and Raman spectroscopy techniques, where the compounds P bT iO3 (PT), CdT iO3 (CT) and cationic substitution were studied in site A between these two materials P bxCd(1−x)T iO3, in the concentrations of x = 1.0, 0.9, 0.8, 0.7, 0.6, 0.5, 0.4, 0.3, 0.2, 0.1 and 0.0. The synthesis was carried out by the unconventional solid-state reaction method, with modification of the reagents P bO and CdO, keeping T iO2 molarity constant. The P bT iO3, at room temperature, is a ferroelectric perovskite that has a tetragonal structure, while the CdT iO3 can be synthesized to have a rhombometric structure of the centrometric or orthorhombic perovskite type. However, the synthesis temperatures used in this work favor only the ilmenite phase of the CT, which is stable at room temperature and at temperatures below 900 ◦C [1]. When replacing the oxides between the lead and cadmium titanates, the transition temperature varies, as well as the other physical properties of the compound, giving rise to a new material. It was found to obtain a solid solution for the concentrations of 0.8 P b and 0.9 P b, being mostly in the concentration of 0.9. It was also observed, at x ≤ 0.7 P b, the coexistence of the structural phases of the two titanates, which indicates the possible formation of a particulate composite. Thus, it is possible to obtain a still ferroelectric material with a perovskite structure with inherent characteristics of the CT, which has a centromymmetric ilmenite structure. It was possible to analyze the phase transitions of these compounds through of soft mode peak (of lower frequency) in the Raman spectrum with the cationic substitution in the structure of ion A and also through stimulus by temperature, determining the new temperatures of phase transition for the concentrations of x = 0.9, 0.5, 0.4 and 0.2, which inform the temperature limits at which the material can be implemented without the total loss of its ferroelectric characteristics. The modifications of the P bT iO3 studied in this work indicate important structural changes such as the reduction of the tetragonality factor (c/a) and the increase in the density of the material.