Preparation, electrical conductivity and tetragonal distortion of some manganite-systems

Abstract The preparation of the tetragonal spinels in the series (1) Cu x Mn 3− x O 4 (0 ⩽ x ⩽ 0,2), (2) Zn 1+ x Mn 2− x O 4 (0 ⩽ x ⩽ 0,2), (3) Mg x Mn 3− x O 4 (0 ⩽ x ⩽ 1) and (4) Zn x Mn 3− x O 4 (0 ⩽ x ⩽ 1) is described. Studies of the crystal symmetry as a function of composition and of electrical conductivity as a function of composition and temperature, are reported. All the compositions exhibit a thermal hysteresis of the electrical conductivity in the range of the tetragonal to cubic transition. Analysis of crystal-chemical and electrical properties leads to the probable cation distribution formulae for each system. The electrical conductivity involves the hopping mechanism of electrons between octahedral-site Mn 3+ and Mn 4+ ions. In the systems (1) and (2) the presence of Cu 2+ and Zn 2+ ions in the octahedral positions together with the equivalent distorting power of the octahedral Cu 2+ and Mn 3+ ions has been established.