| Summary: | 碩士 === 國立東華大學 === 物理學系 === 101 === In this thesis, the measurements of magnetization (M), electrical resistivity (ρ), Seebeck coefficient (S), and thermal conductivity () on the Nb and Ru doped noncentrosymmetric superconducting Mo3Al2C compounds, namely Mo3-xNbxAl2C (x = 0.00 - 0.25) and Mo3-xRuxAl2C (x = 0.00 - 0.15), have been performed in the temperature range 4-300 K. A significant diamagnetic signal for the pure Mo3Al2C is observed below the onset of its critical temperature; confirming bulk superconductivity at 9.0 K. It is found that the superconducting transition temperature decreases gradually and the superconducting volume fraction reduces substantially with increase in the content of Nb and Ru. In particular, the superconducting volume fraction reduces by a factor of about 500 for the Mo2.75Nb0.25Al2C compound. Besides, and the superconducting transition width is broadened with Nb and Ru substitution, presumably due to the introduction of impurity phases upon doping.
The normal state resistivity has a weaker temperature dependence for the doped compounds compared to the pure Mo3Al2C, suggesting that the electrical transport is sensitive to impurities and disorders in the system. For all studied samples, the value of Seebeck coefficient is found to be negative over the measured temperature range, indicating that the electron-type carriers dominate the thermoelectric transport. It is noted that the room-temperature S values of Nb (Ru) doped Mo3Al2C compounds increase (decrease) systematically with increasing Nb (Ru) content, implying a decrease (increase) of the density of states (DOS) at Fermi level. Finally, it is found that both charge carriers and lattice phonons are participated in thermal transport of the pure and doped Mo3Al2C compounds.
|
|---|
