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Published on: May 15, 2017
Cd5Te4O12X2 (X = Cl, Br, I): a new oxyhalide family with [CdO4X] mixed anionic units and adjustable optical
Maqsood Iqbal1,2, Jiazheng Zhou2, Hongshan Wang1,2
1Research Center for Crystal Materials; CAS Key Laboratory of Functional Materials and Devices for Special Environments, Xinjiang Key Laboratory of Functional Crystal Materials, Xinjiang Technical Institute of Physics & Chemistry, CAS, Urumqi 830011, China. lijunjie@ms.xjb.ac.cn.
Abstract:
Three novel tellurate halides Cd5Te4O12X2 (X = Cl, Br, I) were rationally designed by introducing planar [TeO3] into the binary anionic compounds, and synthesized by the flux method in sealed systems. The compounds crystallize in the centrosymmetric P21/c space group and show a layered 3D structure built by pyramid-shaped [CdO4X] (X = Cl, Br, I), octahedral [CdO6], and triangular [TeO3] units. The compounds belong to a new emerging oxyhalide family, AII5BIV4OII12XI2, and the pseudo-ternary phase diagram of the CdO-TeO2-CdX2 system is provided. Among them, Cd5Te4O12Cl2 shows a large birefringence of 0.113 at 1064 nm. Notably, the compounds show adjustable optical properties. With the increase of the atomic number of the halide, the birefringence is reduced from 0.113 to 0.0942, 0.042 at 1064 nm, and the band gap fluctuates from 4.25, 4.21, to 3.77 eV for Cd5Te4O12Cl2, Cd5Te4O12Br2, and Cd5Te4O12I2, respectively. The theoretical calculations indicate that they are direct band gap compounds, which are mainly determined by the pyramidal [CdO4X] and planar [TeO3] units. The results enrich the chemical and structural diversity of mixed anionic compounds and give some new insights into the design of new materials by combining mixed anionic units with planar [TeO3] units.
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