Structural and Raman study of the thermoelectric solid solution Sr1.9La0.1Nb2O7

Ceramic powder samples of the perovskite‐slab‐layered polycrystalline Sr1.9La0.1Nb2O7 (SLNO1) thermoelectric solid solution were prepared via solid‐state reaction. The Raman effect was studied as a function of temperature between 27°C and 400°C (at ambient pressure) and pressures up to 11.6 GPa (at room temperature). The atomic disorder introduced by the La atoms produced phonon lines that were broader than those of Sr2Nb2O7 (SNO). We detected a temperature‐induced phase transition at Ti−c = 247 ± 5°C (ambient pressure) and a pressure‐induced phase transition at Pi−c = 6.74 ± 0.25 GPa (room temperature), which correspond to the reported SNO incommensurate‐to‐commensurate phase transitions at 215°C (atmospheric pressure) and Pi−c = 6.54 ± 0.25 GPa (27°C), respectively. In this paper, the phenomenological and structural differences between SNO and SLNO1 are discussed based on density functional theory calculations of Sr2−xLaxNb2O7 (x = 0.0625 and 0.125) supercells. Changes in the incommensurate‐to‐commensurate Cmc21 phase transition temperature (Ti−c, at ambient pressure) and pressure (Pi−c, at ambient temperature) originated from the ionic substitution of Sr ions by La ions in Sr2Nb2O7 (SNO) to form Sr2−xLaxNb2O7 (x = 0.1, SLNO1) were studied by Raman spectroscopy. The behavior with temperature and pressure of the phonon wavenumber reveals increments of 32 °C in the Ti−c and 0.2 GPa in the Pi−c phase transitions. Phenomenological and structural differences between SNO and SLNO1 are discussed using Density Functional Theory calculations of Sr2−xLaxNb2O7 (x = 0.0625 and 0.125) supercells.