Cs2Hg3S4: A Low-Dimensional Direct Bandgap Semiconductor

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• 作者：Saiful M. Islam ; S. Vanishri ; Hao Li ; Constantinos C. Stoumpos ; John. A. Peters ; Maria Sebastian ; Zhifu Liu ; Shichao Wang ; Alyssa S. Haynes ; Jino Im ; Arthur J. Freeman ; Bruce Wessels ; Mercouri G. Kanatzidis
• 刊名：Chemistry of Materials
• 出版年：2015
• 出版时间：January 13, 2015
• 年：2015
• 卷：27
• 期：1
• 页码：370-378
• 全文大小：586K
• ISSN：1520-5002

文摘

Cs₂Hg₃S₄ was synthesized by slowly cooling a melted stoichiometric mixture of Hg and Cs₂S₄. Cs₂Hg₃S₄ crystallizes in the Ibam spacegroup with a = 6.278(1) 脜, b = 11.601(2) 脜, and c = 14.431(3)脜; d_calc = 6.29 g/cm³. Its crystal structure consists of straight chains of [Hg₃S₄]_n^{2n鈥?/sup> that engage in side-by-side weak bonding interactions forming layers and are charge balanced by Cs+ cations. The thermal stability of this compound was investigated with differential thermal analysis and temperature dependent in situ synchrotron powder diffraction. The thermal expansion coefficients of the a, b, and c axes were assessed at 1.56 脳 10鈥?, 2.79 脳 10鈥?, and 3.04 脳 10鈥? K鈥?, respectively. Large single-crystals up to 鈭? cm in length and 鈭? cm in diameter were grown using a vertical Bridgman method. Electrical conductivity and photoconductivity measurements on naturally cleaved crystals of Cs₂Hg₃S₄ gave resistivity 蟻 of 鈮?08 惟路cm and carrier mobility-lifetime (渭蟿) products of 4.2 脳 10鈥? and 5.82 脳 10鈥? cm2 V鈥? for electrons and holes, respectively. Cs₂Hg₃S₄ is a semiconductor with a bandgap E_g 鈭?2.8 eV and exhibits photoluminescence (PL) at low temperature. Electronic band structure calculations within the density functional theory (DFT) framework employing the nonlocal hybrid functional within Heyd鈥揝cuseria鈥揈rnzerhof (HSE) formalism indicate a direct bandgap of 2.81 eV at 螕. The theoretical calculations show that the conduction band minimum has a highly dispersive and relatively isotropic mercury-based s-orbital-like character while the valence band maximum features a much less dispersive and more anisotropic sulfur orbital-based band.}