ELECTRICAL-PROPERTIES OF COPPER MANGANITE SPINELS CUXMN3-XO4 (0-LESS-THAN-X-LESS-THAN-1)

The electrical conductivity and thermoelectric power of single-phase copper manganite spinels Cu(x)Mn(3-x)O4 with 0 < x < 1 are measured as a function of temperature at low oxygen partial pressure (10(-3) Pa for x < 0.50 and 1 Pa for x > 0.50). For x > 0.70, electrical conduction is explained by the small polaron hopping of electron holes (p-type) between Mn4+ and Mn3+ ions on octahedral sites, yielding a hopping energy E(H) that varies between 0.23 eV for x = 0.96 to 0.26 eV for x = 0.75. Over the composition range 0 < x < 0.75, the electrical conductivity drops by three (x = 0.45) to ten (x = 0) orders of magnitude with a concurrent increase in the activation energy which suggests a band-type conduction rather than hopping conduction. The different electrical behaviour at high oxygen pressure (10(5) Pa) is found to arise from the presence of two phases alpha-Mn2O3 and Cu1.5Mn1.5O4.