Crossover form dominant magnon drag to phonon drag in bismuth rich La0.85Na0.15MnO3 manganite.

The thermoelectric power (TEP) or seebeck coefficient (S) characteristic of bismuth substituted La0.85-xBixNa0.15MnO3 manganites (x = 0, 0.1, 0.2, 0.25, and 0.3) were studied to understand the effect of bismuth on influencing the conduction of charge carries in large bandwidth manganite La0.85Na0.15MnO3. A pragmatic equation S = S0 + S1T + S3/2T3/2 + S3T3 + S4T4 was exploited to obtain the contributions to thermopower at low temperature ferromagnetic state of the specimen. Both electrons and holes involve in conduction at different regime of temperature from 14K to 295K. A large increase of maximum TEP, Smax changing from 3 µV.K−1 to 67 µV.K−1 was realized at 30% substitution of Bi. This large increase in the TEP value is due to the appearance of phonon drag effect at low temperature in Bismuth rich La0.85Na0.15MnO3. The signature of both magnon drag and phonon drag is seen at low temperature. At high temperature small polarons are governing the conduction in the investigated specimen. Bismuth substitution in soft ferromagnetic manganites such as La0.85Na0.15MnO3 increases the activation energy thereby improving the TEP. [ABSTRACT FROM AUTHOR]