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 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 degrees C and 400 degrees 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 degrees 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 degrees C (atmospheric pressure) and Pi-c = 6.54 +/- 0.25 GPa (27 degrees 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.