Role of phonon drag and carrier diffusion in thermoelectric power of polycrystalline La0.97Na0.03MnO3 manganites

Dinesh Varshney,Dinesh Choudhary

doi:10.1007/s40145-014-0113-1

Abstract

We develop a theoretical model for quantitative analysis of temperature-dependent thermoelectric power of monovalent (Na) doped La0.97Na0.03MnO3 manganites. In the ferromagnetic regime, we have evaluated the phonon thermoelectric power by incorporating the scattering of phonons with impurities, grain boundaries, charge carriers and phonons. In doing so, we use the Mott expression to compute the carrier (hole) diffusion thermoelectric power (S c diff ) using Fermi energy as carrier (hole)-free parameter, and S c diff shows linear temperature dependence and phonon drag S c drag increases exponentially with temperature which is an artifact of various operating scattering mechanisms. It is also shown that for phonons the scattering and transport cross-sections are proportional to ω4 in the Rayleigh regime where ω is the frequency of the phonons. Numerical analysis of thermoelectric power from the present model shows similar results as those revealed from experiments.

Highlights

The mixed-valence perovskite manganites Ln1 xAxMnO3 have recently attracted considerable attention because of a huge negative magnetoresistance near the Curie temperature [1]
It is known that the host atom La and the doped atom Na have approximately equal ionic radius
The electrons in the valence band are excited into the impurity band which generates hole-like carriers, which is responsible for a positive S

Summary

Introduction

The electrons in the valence band are excited into the impurity band which generates hole-like carriers, which is responsible for a positive S Keeping all these facts in mind, a systematic study of influence of monovalent Na doping in parent LaMnO3 on thermopower of La0.97Na0.03MnO3 has been carried out and the results of such an investigation are presented here. The estimation and numerical computation of the phonon drag and carrier (hole) diffusion contributions to the thermoelectric power by incorporating the effects of different scattering mechanisms are presented

Results and discussion

Conclusions