Role of MnTi and MnSn substitutions on the electrical properties of Ni-Zn ferrites

Electrical resistivity and thermoelectric power measurements are made on the systems Ni0.82+Zn0.22+Mnx2+Snx4+Fe2-2xO42-, Ni0.62+Zn0.42+Mnx2+Snx4+Fe2-2x3+O42-, and Ni0.62+Zn0.4Mnx2+Tix4+Fe2-2x3+O42- with x = 0, 0.1, 0.2, 0.3, and 0.4 in the temperature range of 300 to 800 K. The increase in resistivity with composition is attributed to increasing concentrations of substitutions in each system. Impurity conduction is favoured in each system up to 425 K except for x = 0.3 and 0.4 concentrations of MnSn in the second system. These samples of the second system show anomalous behaviour in this temperature region.. At higher temperatures conduction is due to hopping of polarons. Anomalous behaviour is also observed in the MnTi substitute system for x = 0.4. Thermoelectric power is found to be negative over the whole range of temperatures indicating that the majority charge carriers are electrons. The temperature variation of thermoelectric power suggests that these ferrites of different systems are nondegenerate semiconductors. The binding energy of the polaron is found to be in the range of 0.1 eV in the case of MnSn substituted samples, in the case of MnTi substituted samples, it is of the order of 0.2 eV. This is attributed to the formation of stable bonds of Ti4+ with Fe2+.