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MATERIALS RESEARCH

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Preparation and characterization of GeS2 Vesna Stani´c, Alain C. Pierre, and Thomas H. Etsell Department of Mining, Metallurgical and Petroleum Engineering, University of Alberta, Edmonton, Alberta, T6G 2G6, Canada

Randy J. Mikula CANMET Western Research Centre, Devon, Alberta, T0C 1E0, Canada (Received 3 April 1995; accepted 16 October 1995)

Synthesis of GeS2 via a sol-gel process using germanium ethoxide and hydrogen sulfide in toluene resulted in a gel aggregate with an apparent GeyS ratio 1 : 1.8. Special precautions were necessary to protect the reaction mixture from water contamination which produced GeO2 . Results indicated that the main source of water was the hydrogen sulfide gas. Heat treatment of the produced GeSx gel yielded a product with GeyS ratio 1 : 2.3. The sol-gel prepared materials and their heat-treated products were characterized by various methods.

I. INTRODUCTION

Semiconductor materials, such as the sulfides of group IV elements, are promising materials for electronic devices and could be used for light transmission in the middle and far infrared spectral range since they are transparent to wavelengths from 2–15 mm. They also have low intrinsic transmission losses. For instance, germanium disulfide has ten times lower absorption than silica in the far IR region.1 The electronic and optical properties of semiconductors are strongly affected by impurities and inhomogeneities in the material, most of which are a result of the preparation process. By using an appropriate synthesis method, the light transmission losses of the prepared material could be minimized to the level of intrinsic optical losses based on the pure material properties. The best material for light transmission applications would be a monocrystal, in order to minimize loss and maximize transparency. Since it is very difficult to produce a monocrystal and to control its refractive index, glasses are used to overcome these shortcomings. The sol-gel process could be expected to provide a homogeneous product with a low level of impurities. Moreover, the product could have a controlled structure and stoichiometry. The first attempt to synthesize a colloidal metal sulfide was reported in 1982 by Matijevi´c and Wilhelmy.2 They synthesized monodispersed CdS particles, using Cd(NO3 )2 and hydrolyzed thioacetamide. By controlling the reaction conditions, including pH, concentration, temperature, and the nature of the anions, particle nucleation and growth were controlled in order to obtain a monodispersed CdS sol. In 1984, Melling3 made the first effort to synthesize metal sulfides from metal alkoxides and H2 S. He produced GeS2 by reacting Ge(OEt)4 dissolved in J. Mater. Res., Vol. 11, No. 2, Feb 1996

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toluene with H2 S gas bubbled through the solution. Since alkoxides easily hydrolyze, Melling had previously purged the reaction apparatus with inert gas. The reaction product was a GeS2 gel with significant GeO2 impurities. Seddon et