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Transport and NMR study of the scandium boron carbide compound Sc 2 B 1.1 C </mml:…

2000; American Physical Society; Volume: 62; Issue: 11 Linguagem: Inglês

10.1103/physrevb.62.7587

1095-3795

Takao Mori, Masataka Tansho, Yoshito Onoda, Ying Shi, Tatsuya Tanaka,

Boron and Carbon Nanomaterials Research

Transport properties and nuclear magnetic resonance (NMR) of the new scandium boron carbide compound ${\mathrm{Sc}}_{2}{\mathrm{B}}_{1.1}{\mathrm{C}}_{3.2}$ were investigated. ${\mathrm{Sc}}_{2}{\mathrm{B}}_{1.1}{\mathrm{C}}_{3.2}$ has a trigonal crystal structure $[a=b=23.710(9)A,$ $c=6.703(2)A,$ $P3m1]$ and is composed of alternate $[{\mathrm{B}}_{1/3}{\mathrm{C}}_{2/3}{]\ensuremath{-}\mathrm{S}\mathrm{c}\ensuremath{-}\mathrm{C}\ensuremath{-}\mathrm{S}\mathrm{c}\ensuremath{-}[\mathrm{B}}_{1/3}{\mathrm{C}}_{2/3}]$ layers, with the boron and carbon mixed layer $[{\mathrm{B}}_{1/3}{\mathrm{C}}_{2/3}]$ forming a very rare graphitelike structure. Physical properties similar to graphite intercalation compounds (GIC) were observed. The temperature dependence of the resistivity showed a large anisotropy. The in-plane resistivity showed a metallic quadratic dependence, also observed in some GIC's while the resistivity along the c axis, perpendicular to the layers, increased with decreasing temperature. From magnetic susceptibility and specific-heat measurements, the orbital susceptibility was indicated to take a paramagnetic value. At low temperatures an increase of the in-plane resistivity with $\mathrm{log}T$ dependence and negative magnetoresistance was observed. Two-dimensional Anderson localization was indicated, possibly originating from disorder in the $[{\mathrm{B}}_{1/3}{\mathrm{C}}_{2/3}]$ graphitelike layer. ${}^{11}\mathrm{B}$ magic angle spinning (MAS) nuclear magnetic resonance (NMR) results indicate a large distribution of the chemical shift of the boron nuclei, which is consistent with the existence of disorder within the graphitic layer.