本論文以固態反應在400°C合成出一個新穎金屬硒化物。其晶系與空間群為Monoclinic C2/m，晶格常數分別為a = 35.799(1) Å, b = 4.1646(2) Å, c = 13.7361(6) Å, β= 109.484(1) °, V = 1930.6(2) Å3及Z = 4。此晶體結構可區分成兩個層狀結構，其中以[BiSe6]八面體、[CuI2Se2]、[CuISe3]四面體及[CuISe5]、[CuI2Se4]八面體構成層狀結構1；另外，以[BiSe5]四角錐、[CuSe4]四面體構成層狀結構2。其中Cu+離子自由地在整個結構中流動，具有嚴重無序化 (disorder)和缺陷 (defect)的現象。
　　純相合成以高熔點之Bi2Se3、CuI、Cu2Se二元物為起始物，在900 °C合成熱穩定的純相。物理性質方面以傅立葉轉換紅外光譜儀測定此化合物為一個窄能隙半導體材料，其能隙約為0.47 eV。以差示熱分析儀測定其熔點為586°C，再結晶點為557°C。目前對此化合物的電子結構做更進一步的分析，並且透過熱壓的方式使其成為具有高利用價值的熱電材料。

關鍵字: 金屬硒化物、銅離子無序化、窄能隙半導體、熱電性質、熱壓

SUMMARY
A new metal selenide was synthesized by a solid-state reaction at 400°C. Crystal Data: monoclinic, C2/m, a = 35.799(2) Å, b = 4.1656(3) Å, c = 13.7378(9) Å, β= 109.4729(9)o, V = 1931.5(3) Å3, and Z = 4. This compound adopts a new three-dimensional structure , which framework is constructed by two distinct layers alternating along the a axis. The first layer is formed by [BiSe6] octahedra, [CuI2Se2] tetrahedra, [CuISe3] tetrahedra, [CuISe5] octahedra, and [CuI2Se4] octahedra. The second layer is formed by [BiSe5] square pyramids and [CuSe4] tetrahedra. All the copper(Ⅰ) ions are deficient in their positions that behavior may help to depress thermal conductivity for the thermoelectrics. The pure phase was successfully synthesized by reacting Bi2Se3, CuI and Cu2Se using a stoichiometric ratio at 900 °C. The optical bandgap was determined by the diffuse reflectance spectra to give a value of ~0.47 eV. The differential thermal analysis reveals that melting point is ~586 °C and the recrystallization point is ~557 °C. The calculation of density of states (DOS) of this new structure is still undertaken. We will apply the technique of hot pressing to prepare the samples for the measurements of Seebeck coefficient, electrical conductivity and thermal conductivity.

Key words: metal selenides, copper(Ⅰ) disordered, narrow bandgap, thermoelectrics properties, hot pressing

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