Raman scattering study of calcium hexaboride |
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| Institution: | 1. Department of Physics, Ewha Womans University, Seoul 120-750, South Korea;2. Division of Nanosciences, Ewha Womans University, Seoul 120-750, South Korea;3. Center for Frontier Materials, Department of Materials Science and Engineering, GIST, Gwangju 500-712, South Korea;1. Computational Optics Research Group, Advanced Institute of Materials Science, Ton Duc Thang University, Ho Chi Minh City, Vietnam;2. Faculty of Applied Sciences, Ton Duc Thang University, Ho Chi Minh City, Vietnam;1. School of Applied Physics and Materials, Wuyi University, Jiangmen 529020, China;2. National Key Laboratory of Shock Wave and Detonation Physics, Institute of Fluid Physics, China Academy of Engineering Physics, Mianyang 621900, China;1. School of Materials Science & Engineering, Nanchang University, Nanchang 330031, PR China;2. Research Center of Rare Earths & Micro/Nano Functional Materials, Nanchang University, Nanchang 330031, PR China;3. Shanghai Engineering Research Center of Magnesium Materials and Applications & National Engineering Research Center of Light Alloy Net Forming, School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240, PR China |
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| Abstract: | We report significant difference in the Raman spectra of two different kinds of CaB6 single crystals grown from boron purity 99.9% (3N) or 99.9999% (6N), respectively. Our Raman spectra of CaB6 (3N), which are similar to those of previous measurement N. Ogita, S. Nagai, N. Okamoto, M. Udagawa, F. Iga, M. Sera, J. Akimitsu, S. Kunii, Phys. Rev. B 68 (2003) 224305], show peaks at 781.3 cm?1 (T2g), 1140.1 cm?1 (Eg), and 1283.5 cm?1 (A1g). The Eg mode shows a characteristic double-peak feature due to an additional weak broad peak centered at 1156.0 cm?1. However, the Raman spectra of CaB6 (6N) show sharp peaks at 772.5 cm?1 (T2g), 1137.9 cm?1 (Eg), and 1266.6 cm?1 (A1g). The peak frequencies are down shifted as much as 17 cm?1. In addition, no additional peak feature is observed for the Eg mode so that the mode is symmetric in the case of CaB6 (6N). The X-ray powder diffraction patterns for both CaB6 (3N) and CaB6 (6N) show that the lattice parameters are essentially the same. The majority of the impurity in the 99.9% (3N) boron is assessed to be C. Thus we prepared Ca(B0.995C0.005)6, CaB6 (6N) doped with C, and looked for the difference in the Raman spectra. The Raman spectra of Ca(B0.995C0.005)6 are nearly identical to those of CaB6 (6N), indicating that the difference in the Raman spectra of CaB6 (3N) and CaB6 (6N) is not due to C impurity. However, presence of impurity, even if small amount, seems to be enough to trigger local-structure changes to lower symmetry inducing the difference in Raman spectra of CaB6 (3N) and CaB6 (6N). |
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