Electron Transport in Perovskite-Type Ca0.5 –xSr0.5LuxMnO3 – δ Manganites

Perovskite-type Ca 0.5 – x Sr 0.5 Lu x MnO 3 – δ ( x = 0.05, 0.10, 0.15, and 0.20) manganites have been prepared in air using a citrate–nitrate process for preparing precursors. At room temperature, the x = 0.05, 0.10, and 0.15 samples have an orthorhombic structure (space group Pbnm ); when x = 0.2, a tetragonal structure (space group I 4/ mcm ) is formed. The increase in unit cell volume in response to rising lutetium concentration in the samples is due to an increase in Mn 3+ concentration necessary to ensure n -type electrical conductivity σ. The temperature-activated electrical conductivity is consistent with the adiabatic transport mechanism of small polarons. The increase in magnitude of the Seebeck coefficient S in response to rising temperature is due to the decrease in the concentration of Mn 3+ ions via their disproportionation to Mn 2+ and Mn 4+ ions. The S ( T ) and σ( T ) temperature dependences under the condition where δ ⁓ 0 have been used to calculate the equilibrium constants of the disproportionation reaction, charge carrier concentrations and mobilities.