THERMOPOWER OF SR1-XLAX TIO3 CERAMICS

The thermopower eta of Sr1-xLaxTiO3 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, eta depe nds linearly on temperature and on n(-2/3), expected from a degenerate quasi free electron gas. In the case of high temperatures and low n, the absolute value of eta rises with 1.5 . ln10 k/e per decade of temp erature and with In10 . k/e per decade of carrier concentration, as ex pected 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 transpo rt factor A(e). In the classical range A(e)=3 can be evaluated, requir ing only a temperature and lanthanum independent m(eff). Thus, the the rmopower of Sr1-xLaxTiO3 ceramics can be described by a constant effec tive mass and a constant transport factor within a wide range of tempe rature and lanthanum content. Furthermore, the transition from degener ation to classical behavior can be described as a function of temperat ure and electron density, e.g., at room temperature it takes place at about x approximate to 0.2 (i.e., n approximate to 3.4 . 10(21)/cm(3)) . (C) 1995 American Institute of Physics.