Análise da incorporação de elementos terras-raras na estrutura de cerâmicas ferroelétricas livres de chumbo

Abstract

Using materials with piezoelectric properties has increasingly attracted the interest of researchers in the scientific and technological fields. However, most of these materials have Lead in their composition, which limits their use due to their high toxicity. Thus, they need to replace these materials with others with the same properties but without Lead in their composition. A viable and increasingly studied alternative is piezoelectric materials from the sodium-potassium niobate (KNN) system. KNN is a promising candidate due to its high Curie temperature, good ferroelectric properties, and large electromechanical coupling coefficients. Recently, lanthanide oxides such as La2O3, Nd2O3, and Yb2O3 have been used as dopants in piezoelectric systems. Doping with rare-earth elements generates punctual defects since they generally have different valences at the A and B sites, depending on their atomic radius. In this work, ceramics of the (x)KNbO3/(1-x)NaNbO3 system doped with 1% by weight of the oxides La2O3, Nd2O3 e Yb2O3 were prepared by the conventional route of mixing oxides for different stoichiometries (x = 48, x = 50 and x = 52) around the KNN morphotropic phase boundary. Structural analyzes by Fourier transform infrared spectroscopy (FTIR), RAMAN spectroscopy, and X-ray diffraction showed the formation of the desired perovskite phase but with variable symmetry depending on the added rare-earth dopant. A study of ferroelectric properties shows that each added dopant generates a type of defect in the system. Such defects vary according to the KNN stoichiometry, and the atomic radius of the rare earth used as a dopant.