Electrical Conduction in Tetragonally Distorted Manganite Spinels

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Abstract
The compounds with spinel lattice structure (1) Cd x Cu1-x Mn2O4, (2) Co x Cu1-x Mn2O4 and (3) Mg x Cu1-x Mn2O4 (0≤x≤1) are prepared. Studies of crystal symmetry as a function of composition and of electrical resistivity as a function of composition and temperature, are reported. The compositions with tetragonal symmetry exhibit thermal hysteresis of electrical resistivity, whereas those with cubic symmetry display usual linear variation of log ρ vs. 1/T. The electrical conduction involves the hopping mechanism of electrons between octahedral site Mn3+ and M4+ ions. It is shown that there is major contribution to activation energy due to the cooperative distorting forces in the tetragonally crystallized systems. CuMn2O4 is shown to have cation distribution Cu z 1+Cu1-z 2+[Mn z 4+Mn2-2z 3+]O4 2- where (0<z<0.1).

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