Seebeck coefficient of Ca1–xPrxMnO3–δ paramagnetic manganites

Resumo

The Seebeck coefficient (S) of Ca_1–xPr_xMnO_3–δ (х = 0, 0.05, 0.10, 0.15) manganites with a perovskite-like structure has been measured in air at temperatures (T) from 300 to 1200 K. The negative sign of their S indicates that all of the samples have n-type conductivity. The observed increase in the magnitude of the Seebeck coefficient with increasing T is interpreted in terms of small-polaron transport with allowance for the decrease in Mn³⁺ concentration as a result of the disproportionation reaction 2Mn³⁺ = Mn²⁺ + Mn⁴⁺. Based on a theoretical analysis of experimental S(T) data, we calculated equilibrium constants for the disproportionation reaction, carrier concentration, and the concentration of sites available for carrier migration as functions of temperature. It has been shown that, for an adequate analysis of electron hopping and calculation of the Seebeck coefficient of the electron-doped manganites, the spin state of the Mn⁴⁺ ions should be taken into account.