Mr. Haikai Zou - M.Sc. Candidate
05/02/2025
אודיטוריום ע"ש דויד וואנג, בניין מידן, קומה 3
12:30 - Jerusalem time / 18:30 - Beijing time
Due to their relatively high thermopower and conductivity, calcium manganite compounds (CaMnO₃) are regarded as promising candidates for high-performance thermoelectric power conversion at high temperatures. Doping with trivalent rare-earth elements at the Ca sites, such as La or Y, introduces charge carriers while significantly reducing thermal conductivity. This is a good strategy for improving their thermoelectric figure of merit.
In this study, neutron diffraction (ND) measurements were performed to probe the evolution of MnO₆ octahedral distortions, including the variations in Mn-O bond lengths and Mn-O-Mn bond angles, as a function of doping level of Ca1-xRxMnO3 with R=La or Y and x ranging from 0.006 to 0.13. The results imply on direct correlation between doping-induced local-order structural modifications and both electrical conductivity and conduction activation energy. It is highlighted that the anomalous trends in electrical conductivity and activation energy with doping level are attributed to Jahn-Teller distortions, which are further supported by Raman spectroscopy and evaluation of the effective bandwidth for charge carriers in the eg orbital of Mn ions. So far, no pressure-induced phase transitions were observed up to 20 GPa for Y-doped sample (x=0.02&0.03), and La-doped sample (x=0.02). Our ND results reveal the correlation between electrical transport properties and doping-induced lattice distortions. This study sheds light on the effects of La and Y dopants on lattice structure and electronic transport of CaMnO3.