Temperature phase transitions in silver niobate and lithium tantalate-modified silver niobate ceramics

The temperature behaviour of 0.955 AgNbO₃-0.045 LiTaO₃ and AgNbO₃ ceramics was studied in the range from 10 to 415 K using Raman spectroscopy. Ab initio calculations of the Raman spectra in the Pmc2₁ phase of AgNbO₃ were carried out using three potentials (A-PZ, PBE, and PBEsol) for spectral interpretation. The peculiarities in the Raman spectra in AgNbO₃ ceramics are observed and explained. The differences in the spectra of the 0.955 AgNbO₃-0.045 LiTaO₃ and AgNbO₃ ceramics are shown. The temperatures of the structural changes in the 0.955 AgNbO₃-0.45 LiTaO₃ and AgNbO₃ ceramics were discussed. A structural phase transition below 120 K was observed in silver niobate. A phase transition was observed at 310 K and below 150 K in 0.955 AgNbO₃-0.045 LiTaO₃.