Estudo de transição de fases por espectroscopia Raman e análise dielétrica em cerâmicas baseadas em AgNbO3

Abstract

Due to the current demand for modern electronic devices that are not harmful to the environment and human beings, new materials have emerged as strong candidates for technological applications. Between them, lead-free materials based on silver niobate (AgNbO3) appear as promising for new applications since they have interesting properties to be explored, especially in energy storage devices. In this context, the aim of the present work is to study, via Raman spectroscopy and dielectric characterization, the structural phases transitions in lanthanum modified silver niobate ceramics (Ag1−3xLaxNbO3) from the room temperature up to 500 °C, for compositions where x = 0 and 0.015. The obtained Raman spectra revealed, in both samples, four regions with anomalies in the active vibrational modes, which have been associated with structural phases transitions, in the temperature ranges of 50-100 °C, 200-250 °C, 300-350°C, and 350-400 °C. In addition, a detailed analysis was performed on the ferroelectric soft-mode, which has been revealed for the wavenumbers around 108 cm−1 and 107 cm−1 for pure and doped AgNbO3, respectively, and whose transition to the paraelectric phase was detected in the range of 300-350 °C for both studied samples. The Raman spectra for the La-doped sample revealed changes in the structural parameters, such as, wavenumber, full-width at half maximum and absolute intensity of the Raman modes, with respect to the undoped AgNbO3 system. The obtained results from the dielectric response revealed an agreement between the observed anomalies in the Raman spectra with the structural phase transitions present in the studied materials. Furthermore, the dielectric measurements showed a shift in the Curie temperature (Tc) to lower values with the inclusion of the doping ion in the ABO3 perovskite structure, thus confirming the influence of the doping ion in the structural and phase transition characteristics of the AgNbO3 system.