Synthesis, crystal structure and properties of Nd_1-xA_xMnO_3-δ (A = Ba, Sr and Ca)

The effect of A-site substitution by alkaline earth metals on properties of NdMnO_3-δ have been investigated. Nd_xA_1-xMnO₃ (A=Ba, Sr, Ca; x=0, 0.25) have been synthesized by a citrate-nitrate combustion technique. The samples were characterized by X-ray powder diffraction (XRPD), thermo-gravimetric analysis and the standard 4-probe DC technique in the temperature range of 25-1000 °C in air. The XRPD patterns revealed that all samples were single-phase and possessed an orthorhombic structure (Pnma space group). The Rietveld refinement of the patterns showed that the unit cell volume reduced with a decrease in the dopant size. The temperature dependencies of mass loss indicated that oxygen release from the samples started only at temperatures above 600°C. The total conductivity of the samples indicated a semiconducting behaviour in the whole temperature range studied. The highest value of total conductivity (205 S/cm) was observed for Nd_0.75Ba_0.25MnO₃ at 1000 °C in air.