Thermopower of Sr_1−xLa_xTiO₃ ceramics

The thermopower η of Sr_1−xLa_xTiO₃ ceramics was investigated up to x=0.5 and in the temperature range between 150 K and 1200 K. In addition, the carrier concentration n was determined by Hall measurements and by a chemical Ti³⁺‐analysis. For low temperatures and high n, η depends linearly on temperature and on n^−2/3, as expected from a degenerate quasi free electron gas. In the case of high temperatures and low n, the absolute value of η rises with 1.5⋅ln10⋅k/e per decade of temperature and with ln10⋅k/e per decade of carrier concentration, as expected from a classical broad‐band semiconductor obeying the Boltzmann statistics. In the range of degeneration an effective mass m_eff of 4.2 electron masses can be deduced without the assumption of a transport factor A_e. In the classical range A_e=3 can be evaluated, requiring only a temperature and lanthanum independent m_eff. Thus, the thermopower of Sr_1−xLa_xTiO₃ ceramics can be described by a constant effective mass and a constant transport factor within a wide range of temperature and lanthanum content. Furthermore, the transition from degeneration to classical behavior can be described as a function of temperature and electron density, e.g., at room temperature it takes place at about x≊0.2 (i.e., n≊3.4⋅10²¹/cm³).