Infrared active phonon modes and ionicity of single crystal MgAl2O4
Bi Cong-Zhi (毕聪志)ab, Ma Ji-Yun (马继云)b, Yan Jun (颜俊)b, Fang Xu (方煦)b, Zhao Bai-Ru (赵柏儒)b, Yao Duan-Zheng (姚端正)a, Qiu Xiang-Gang(邱祥冈)b
a Department of Physics, Wuhan University, Wuhan 430072, China; b National Laboratory for Superconductivity, Institute of Physics, Chinese Academy of Sciences, Beijing 100080, China
Abstract Near-normal incident infrared reflectivity spectra of (100) MgAl2O4 spinel single crystal have been measured at different temperatures in the frequency region between 50 and 6000cm-1. Eight infrared-active phonon modes are identified, which are fitted with the factorized form of the dielectric function. The dielectric property and optical conductivity of the MgAl2O4 crystal are analysed. From TO/LO splitting, the effective Szigeti charges and Born effective charges at different temperatures are calculated for studying the ionicity and the effect of polarization. Based on the relationship between the (LO--TO)1 splitting, which represents the transverse and longitudinal frequencies splitting of the highest energy phonon band in the reflectivity spectrum, and the ionic-covalent parameter, the four main phonon modes are assigned. MgAl2O4can be considered as a pure ionic crystal and its optical characters do not change with decreasing temperature, so it may be used as a suitable substrate for high-Tc superconducting thin films.
Received: 21 November 2005
Revised: 03 March 2006
Accepted manuscript online:
Fund: Project supported by the National Natural Science Foundation of China (Grant No 10474128) and Chinese Academy of Sciences.
Cite this article:
Bi Cong-Zhi (毕聪志), Ma Ji-Yun (马继云), Yan Jun (颜俊), Fang Xu (方煦), Zhao Bai-Ru (赵柏儒), Yao Duan-Zheng (姚端正), Qiu Xiang-Gang(邱祥冈) Infrared active phonon modes and ionicity of single crystal MgAl2O4 2006 Chinese Physics 15 1090
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