| Summary: | 碩士 === 國立中正大學 === 物理所 === 97 === Abstract
LaNiC2, which crystallizes in an orthorhombic CeNiC2 type structure with space group Amm2, is the first nickel-based ternary carbide superconductor with Tc ~ 2.7 K. This material is of much interest due to its unconventional and noncentrosymmetric superconductivity. Our investigation as revealed in the powder X-ray diffraction and crystallographic data of the structural phase stability in LaNiC2 showed that this compound LaNiC2 admits considerable vacancies up to 15% on the C sublattice while still retaining its orthorhombic symmetry.
Therefore, the main purpose of this study by N substitution at the C-site in the LaNiC2 system is to give further understanding of the effects of alloying as well as the superconducting behavior of LaNiC2.Three nitrogen-doped compounds LaNiC1.9Nx, LaNiC1.8Ny and LaNiC1.7Nz have been prepared by 2-step arc-melting process. Room-temperature powder x-ray diffraction patterns with CuKα radiation indicated that each sample was single- or nearly single-phase in an orthorhombic CeNiC2-type structure with space group Amm2. The Tcs (10-90% values), as determined by the zero-field-cooled (ZFC) magnetization data, for these three compounds are: LaNiC1.9Nx (Tc = 3.41-3.50 K), LaNiC1.8Ny (Tc=3.82-4.01 K) and LaNiC1.7Nz (Tc = 3.92-4.09 K).
Compared to the parent compound LaNiC2 (Tc = 3.01-3.25 K), nitrifying the carbon-deficient LaNiC2-δ compound has the advantage of improving the superconducting transition temperature Tc.
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