本研究別以助熔長晶法，合成出具新穎結構化合物(1) Ba3.5Cu7.625+3δIn1.125-δSe9。化合物(1)以助熔長晶法，在高溫800⁰C下合成晶體，晶體的晶系及空間群為Orthorhombic Pnma，單位晶格的a、b、c軸長為a= 46.1700(12) Å, b= 4.26710(10) Å, c= 19.8125(5) Å。結構利用CuSe3、 MSe4 (M=Cu, In)，以共用Se相互連接形成3D立體結構骨架，沿b軸的結構孔道中填有Ba2+陽離子及以共用Se形式連結，沿b軸無限延伸的InSe4。化合物(1)因部分位置有Cu/In的錯排及混填的情形，造成分子式電荷沒有平衡，故以佔有率及價數平衡原則做分子式計算。
除了化合物(1)外，本研究另外以高溫長晶法，合成出一新穎結構化合物(2) Ba3Ag3In1Te6。將藥品置入事先鍍有碳膜的石英管中抽真空密封後，在高溫650⁰C下合成晶體，晶體的晶系及空間群為Orthorhombic Cmc21，單位晶格的a、b、c軸長為a= 4.5669(5) Å, b= 27.937(3) Å, c= 13.3819(13) Å。由MTe4 (M= Ag, In)以共用Te形式連結形成3D結構，結構孔道中填有Ba2+陽離子。

SUMMARY

Two new quaternary metal chalcogenides─Ba3.5Cu7.625+3δIn1.125-δSe9 (1) and Ba3Ag3In1Te6 (2), have been synthesized using KBr flux at 800 ⁰C, and using carbon-coating silica tubes at 650 ⁰C respectively.(1) crystallizes in in the Orthorhombic Pnma space group with a= 46.1700(12) Å, b= 4.26710(10) Å, c= 19.8125(5) Å, and (2) crystallizes in in the Orthorhombic Cmc21 space group with a= 4.5669(5) Å, b= 27.937(3) Å, c= 13.3819(13) Å. While the compound(1) shows a three-dimensional (3D) structure composed of CuSe4 tetrahedra, CuSe3 trigonal with the structural tunnel filled with Ba2+ and InSe4 tetrahedra along b-axis, the compound (2) also shows a three-dimensional (3D) structure composed of AgTe4 and InTe4 tetrahedra with the structural tunnel filled with Ba2+ along a-axis. There is complicated structure such as disorder of Cu/In and deficiency of Cu sites in compound (1) and heavey atoms like Ag and Te in compound (2), both situations would expect to decrease lattice thermal coductivity κl, and so the two new quaternary metal chalcogenides would be expected to exhibit high figure of merit (ZT) of thermoelectric materials(TE).

KWORDS: metal chalcogenides,

INTRODUCTION

There is so many effort to research in metal chalcogenides due to their potential in widespread applications, including Thermoelectric devices, rechargeable batteries, nonlinear optical materials and Transparent conducting oxide of solar cells. Copper-containing chalcogenides also exhibit many special physical properties in many past researches. The simple representive compound Cu2-xSe was reported and investigated not only in its structure but also physical properties because of its Cu deficiency and its charge unbalance situation. After so many researches in Cu2-xSe, Cu2Te and Ag2Te were reported to use as Thermoelectric materials in 1998 and 2005 respectively.
From 2001, there were a series of Ba-Cu-Te compounds were synthesized, including BaCu2Te2, A2BaCu8Te10(A=K, Rb, Cs), Ba3Cu14-xTe12, Ba6.76Cu2.42Te14, Ba2Cu4-xTe5 and Ba2Cu7-xTe6. All of them are usually show Cu clusters and Cu deficiency.
Base on the Ba-Cu-Te researches, here we represent two compounds, Ba3.5Cu7.625+3δIn1.125-δSe9 (1) and Ba3Ag3In1Te6 (2), which are the first members discovered in quaternary Ba/M/In/Q (M=Cu, Ag; Q=Se, Te) systems. Just like other Ba-Cu-Te systems, compound (1) also exhibit Cu clusters, Cu deficiency and structural holes. The compound (2) contains heavy atoms Ag and Te, and also structural holes. Both complicated structure in compound (1) and compound (2) contains heavy atom would expect to decrease lattice thermal coductivity κl and increase the figure of merit (ZT).

MATERIALS AND METHODS

Synthesis. The chemicals used in the reactions of compound (1) were barium (pieces, Aldrich, 99.9%), copper (40-80mesh, 99.9%), indium (shot, Aldrich, 99.9+%), selenium (pellets, Aldrich, 99.9%), potassium bromide (powder, 99.6%, J.T. Baker). Manipulation of barium were under dry N2 atmosphere in an OMNI-LAB glovebox.The reactants were loaded in fused silica tubes (diameter: 8 mm) and sealed under vacuum (<10-4 Torr). Tubes were heated to 300 ⁰C within 5 hours from room temperature, hold in 300 ⁰C for 6 hours. Raised form 300 ⁰C to 800 ⁰C within 20 hours, stayed in 800 ⁰C for 96 hours, the reaction were then cooled to 300 ⁰C within 50 hours then turned off the power, and the products were naturally cooled to room temperature.

The chemicals used in the reactions of compound (2) were barium (pieces, Aldrich, 99.9%), silver (mesh, Aldrich, 99.9%), indium (shot, Aldrich, 99.9+%), tellurium (shot, Aldrich, 99.9%). Manipulation of barium were under dry N2 atmosphere in an OMNI-LAB glovebox.The reactants were loaded in fused silica tubes (diameter: 8 mm) and sealed under vacuum (<10-4 Torr). The silica tubes would be coated a carbon film in advanced to prevent active glass attack of barium in high temperature reaction. Tubes were heated to 650 ⁰C (total weight of reactants under 1 g) or 800 ⁰C (total weight of reactants over 1 g) within 6 hours, stayed for 96 hours, and then cooled by the speed 10 ⁰C/hour to 300 ⁰C, and the products were naturally cooled to room temperature.

Physical Measurement. Electron Microscopy. Semiquantitative analyses of crystal were performed using a Hitachi SU-1500 scanning electron microscope equipped with a Horiba EMAX-ENERGY energy dispersive spectrometer (EDS). The data were acquired using an accelerating voltage of 10 kV. The EDS results analyzed by the EMAX Suite version 1.9 gave the average composition of Ba3.00(10)Ag2.88(11)In1.04(10)Te5.82(12) for (2). The compound (1) didn’t observe a consistent result in the EDS analysis because there were Cu/In disorder in crystal.

X-ray Crystallography. Single crystal s of compound (1) and (2) were selected for indexing and data collection on a Bruker APEXII CCD diffractometer, irradiating with graphite-monochromatized Mo Kα radiation (λ = 0.71073 Å). Data integrations and empirical absorption corrections were performed using the SAINT and SADABS functions, respectively, in the APEX2 package. The structures were solved and refined using the SHELXTL-97 package.
The measured powder patterns of compound (1) and (2) were collected using a Simadzu XRD-7000s X-ray diffractometer, which compared well with the patterns simulated from the results of single-crystal X-ray structural analyses.

RESULTS AND DISCUSSION

Compound (1) adopts a three-dimensional (3D) framework structure, assembled by CuSe4 tetrahedron and CuSe3 trigonal with Ba2+ cations and InSe4 distributed within the framework. The framework can be separated into four copper clusters with deficient Cu7 which is half occupied, Cu/In disorder in Cu8/In8, Cu16/In16, and mixed Cu4/In4, Cu12/In12 (Table1).
Compound (2) also adopts a three-dimensional (3D) framework structure, assembled by AgTe4 and InTe4 tetrahedron with Ba2+ cations distributed within the framework to charge balance. The pure phase of compound (2) was comfirm by Total Pattern Analysis Solutions (TOPAS)(Figure1).

Table1 Coordination and Occpancy of 4, 7, 8, 12, 16

Figure 1 Pure phase of compound (2)

CONCLUSION
Two new quaternary metal chalcogenides, compound (1) and compound (2), had been successfully synthesized with complicated structure in compound (1) and heavy atoms in compound (2). The investigation of the two compounds would continue to synthesize bulk materials so that can be use to make measurement such as Hole Effect, thermal conductivity, and the figure of merit (ZT).

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