Fabrication of Ca-Mn-Nb-O compounds and their structural, electrical, magnetic and thermoelectric properties

CaMn_1−xNb_xO_3−δ (0 ≤ x ≤ 1) were synthesized by conventional solid state reaction method. The structural properties were determined by FTIR, Raman, XRD, XAS measurements. The FTIR and Raman modes change by increasing Nb content and the lattice volume increases by increasing Nb content. The solubility limit of Nb is determined as x ≤ 0.3 and impurity phases start to appear above this limit. The temperature dependence of the magnetization data shows an antiferromagnetic transition below 120 K for low Nb content. Increasing the Nb content causes a change in the magnetic phase from antiferromagnetic to paramagnetic. The oxygen deficiency in CaMnO_3−δ may cause the formation of polaron effect which is destroyed by the Nb ions. The difference graph of XAS data for x = 0 and 0.5 show that the number of Mn³⁺ ions increases by increasing Nb content to maintain the charge neutrality. (paper)