STRUCTURAL-PROPERTIES OF NICKEL MANGANITE NIXMN3-XO4 WITH 0.5-LESS-THAN-OR-EQUAL-TO-1

Single-phase nickel manganite spinels, NixMn3-xO4, with 0.5 ≤x ≤ 1, were prepared by a careful thermal processing of nickel-manganese coprecipitated oxalate precursors. Powder X-ray diffraction analysis of the spinel revealed the presence of cubic single spinel phase with parameter a which decreases with nickel content. The lattice parameter variation can be explained in terms of the distribution of Ni2+ ions on the octahedral sites. Therefore, a fine analysis of data shows that some Ni2+ ions (for x>0.56) are located in tetrahedral sites. The percentage of nickel in A-sites increases with nickel content (x) following the relation % Ni2+ in A sites =P = - 82.1 x2+192.4 x-81.5 and thus the general formula for cation distribution is {Mathematical expression} with y=xP/100 This relationship explains the electrical properties of semiconducting nickel manganite ceramics. © 1990 Chapman and Hall Ltd.