Heat conductivity of La1-xSrxMnO3 surface layers

Using the transient thermoelectric effect (TTE), we have measured the therm oelectric power S(T) and the heat conductivity K(T) of La-1-xSrxMnO3 cerami c 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 characterist ic temperatures, the surface layer S(T) is still similar to the bull, therm opower while the heat conductivity kappa (T) is markedly different, even ch anging the slope at intermediate temperatures. As S is less structure sensi tive 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 dopin g, i.e. x = 0.075 and 0.1. (C) 2001 Elsevier Science B.V. All rights reserv ed.