Electrical Conductivity and Thermal Expansion of Spinels at Elevated Temperatures

Binary oxide spinels composed of Mg, Al, Cr, Mn, Fe, Co, Ni, Cu, and Zn were synthesized. Electrical conductivity was measured in air at 500°–800°C. Thermal expansion was measured from room temperature to 1000°C. Ferrite spinels have thermal expansion coefficients of 11–12 ppm/K, compared with 7–9 ppm/K for other spinels except Cu–Mn and Co–Mn which show anomalous behavior. The highest electrical conductivity among transition metal spinels was found for MnCo 2 O 4 (60 S/cm at 800°C) and Cu 1.3 Mn 1.7 O 4 (225 S/cm at 750°C).