Effect of Crystal Orientation on Seebeck Coefficient and Electrical Conductivity of SrTiO3 Single Crystals

Strontium titanate is a promising thermoelectric material used in harsh environment owing to its high thermoelectric performance and excellent stability at high temperatures. Hence, it has potential application in power generation and sensor through direct conversion between heat and electricity. However, due to its perovskite structure, the relationship between thermoelectric properties and crystal orientation has rarely been studied. In this paper, we prepared La (0–5 mol %)-doped SrTiO3 single crystals with the introduction of oxygen vacancies. Electrical conductivity is improved by both La doping and the introduction of oxygen vacancy. More importantly, the thermoelectric properties of the samples show strong anisotropy. After annealing in carbon at 1773 K for 8 h, the power factor (PF) of the SrTiO3 single crystal at 323 K in the [270] direction is 2.3 mW m–1 K–2, much higher than that in the [160] direction (1.3 mW m–1 K–2). A similar phenomenon was also observed in the La-doped single crystals, but the difference becomes smaller. The PF of the 2 mol % La-doped single crystal after annealing in carbon powder is 2.5 mW m–1 K–2 in the [270] direction and 2.3 mW m–1 K–2 in the [160] direction. The two common directions, [110] and [100], are not suitable for the high TE properties of the SrTiO3 single crystals. The results are valuable for the design of perovskite thermoelectric materials.