Structural and Raman study of the thermoelectric solid solution Sr 1.9 La 0.1 Nb 2 O 7

Ceramic powder samples of the perovskite‐slab‐layered polycrystalline Sr 1.9 La 0.1 Nb 2 O 7 (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 Sr 2 Nb 2 O 7 (SNO). We detected a temperature‐induced phase transition at T i−c = 247 ± 5°C (ambient pressure) and a pressure‐induced phase transition at P i−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 P i−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 Sr 2−x La x Nb 2 O 7 ( x = 0.0625 and 0.125) supercells.