Characterization of electron and phonon transports in Bi-doped CaMnO3 for thermoelectric applications

Electron and phonon transports in CaMnO3 and its Bi-doped counterpart, Bi0.03Ca0.97MnO3, are investigated by thermoelectric transport measurements, Raman spectroscopy, and first-principles calculations. In particular, we focus on CaMnO3 and Bi0.03Ca0.97MnO3's electronic structures, temperature-dependent electron and phonon lifetimes, and their sound velocities. We find that the anti-ferromagnetic insulator CaMnO3 breaks the Wiedemann-Franz (WF) law with the Lorenz number reaching four times that of ordinary metals at room temperature. Bismuth doping reduces both the electrical resistivity and the Seebeck coefficient of CaMnO3, thus it recovers the WF law behavior. Raman spectroscopy confirms that Bi0.03Ca0.97MnO3 has a lower Debye frequency as well as a shorter phonon lifetime. As a result, Bi0.03Ca0.97MnO3 exhibits superior thermoelectric properties over the pristine CaMnO3 due to the lower thermal conductivity and electronic resistivity.Comment: 7 pages, 7 figure

Critical behavior and magnetocaloric effect in La0.7Ba0.25Nd0.05Mn1-xCuxO3

In this work, the magnetic and magnetocaloric properties of La0.7Ba0.25Nd0.05Mn1-xCuxO3 samples (x = 0 - 0.07) synthesized by the sol-gel method are presented. The compounds exhibited a second-order phase transition (SOPT) of ferromagnetic-paramagnetic (FM-PM) phase transition following Banerjee’s criterion. Curie temperature TC decreased with increasing doping concentration. The critical behavior analysis using modified Arrott plots (MAP) showed a short-range FM ordering. Significant entropy change of samples was observed near the TC, which decreased with Cu content. The SOPT nature of compounds was confirmed by both the universal curves and scaling hypothesis