Temperature dependence of the thermoelectric power of La1-xKxMnO3 compounds in light of a two phase model

The temperature-dependent resistivity and thermoelectric power (TEP) of monovalent (K) doped La1-xKxMnO3 polycrystalline pellets (x=0.05, 0.10 and 0.15) between 50 and 310K are reported. K substitution enhances the Curie temperature (TC) from 260 to 309K. Adiabatic small polaron hopping governs the resistivity as well as the TEP in the paramagnetic phase. In the ferromagnetic region, an expression containing the residual resistivity, electron-electron, and electron-magnon scattering term explains well the thermal variation of the electrical resistivity. The TEP at low temperatures in ferromagnetic region (Slt) can be well represented with an expression containing the electron-magnon and spin-wave fluctuation scattering and confirms dominance of electron-magnon scattering. Both, resistivity and TEP data between 50 and 310K are further examined in light of a two-phase model based on an effective medium approximation, in which the conductivity in the transition region is supposed to originate due to the mixing of the metallic region, embedded in a semiconductive polaronic matrix and is characterized by 'mixing factor'. Our analysis confirms that the temperature dependence of the TEP of La1-xKxMnO3 compounds computed using the expression derived using effective medium approach, gives a fairly good description of the observed thermal variation of TEP in monovalent (K) doped lanthanum manganites between 50 and 310K