Heat conductivity of La1-xSrxMnO3 surface layers

Abstract

Using the transient thermoelectric effect (TTE), we have measured the thermoelectric power S(T) and the heat conductivity K(T) of La-1-xSrxMnO3 ceramic surface layers with nominal compositions x = 0.075, 0.1, 0.15, 0.2 and 0.3 in the temperature range 50 340 K. Except for a shift in the characteristic temperatures, the surface layer S(T) is still similar to the bull, thermopower while the heat conductivity kappa (T) is markedly different, even changing the slope at intermediate temperatures. As S is less structure sensitive than kappa, we relate these differences to an increased number density of defects near the surface. In particular, a stoichiometry gradient close to the surface and oxygen vacancy related (two level tunneling-) modes are indicated. In addition, new S and kappa data are presented for lower doping, i.e. x = 0.075 and 0.1. (C) 2001 Elsevier Science B.V. All rights reserved.