Study On Preparation, Structure And Properties Of Ge-Sb-Se Chalcogenide Glasses

Chalcogenide glasses are amorphous materials containing one or more chalcogenelements (S, Se, and Te) as major constituents bonded with other network formingelements like Si, Ge, As, Sb, and so on. They have attractive properties includingexceptional wide transmission range, higher transmittance in infrared region, fasteroptical response time, lower optical loss, higher linear and non-linear refractive indices,better structural stability and thermal stability, and special photosensitivity.Consequently, they are promsing for application in the area of modern integratedoptoelectronics devices such as infrared sensors, infrared imaging, energy transmission,electrostatic photocopying, holographic storage, nonlinear optics, near-field microscopyimaging, optical frequency multiplier, inorganic photoetching and antireflection film.Ge-Sb-Se chalcogenide glasses are mainly consist of weaker two-coordinated Seatoms chain-like structural units, GeSe4/2tetrahedra and SbSe3/2pyramids, leading to themechanical and thermal properties are not ideal because weaker covalent bonds in glassnetwork, restricting the application of glasses. Therefore, we need to further explore andscreen the glass compositions with stable structure, good mechanical, thermal andoptical properties.In this paper, several sets of Ge-Sb-Se chalcogenide glasses were prepared by themelt-quenching technique. The glass compositions cover a rather wide range fromSe-rich to Se-poor with an MCN spanning from2.2to2.75. Based on chemicalcompostion and MCN, the structural, mechanical, thermal and optical properties of theglasses were systematically studied by means of a variety of testing and analyticaltechniques. The main results obtained are as follows:①In Se-rich glasses, the formation of heteropolar bonds like Ge-Se and Sb-Se isfavoured over that of homopolar bonds like Ge-Ge and Sb-Sb in Ge-Sb-Se glassnetwork. With decreasing Se content, glass structure gradually changes from Se-chainor-ring dominated to GeSe4/2tetrahedra and SbSe3/2pyramids cross-linked, leading toan increase in the degree of cross-linkage. In the glasses with chemically stoichiometriccomposition (Ge25Sb10Se65, Ge20.83Sb15Se64.17, Ge16.67Sb20Se63.33) where all Se can beconsumed out, backbone of glass basically dominated by heteropolar Ge-Se and Sb-Sebonds, and thus those glasses have an ideal structure with a minimum number of wrongbonds (Ge-Ge, Sb-Sb and Se-Se). In Se-poor glasses, homopolar bonds Ge-Ge are formed before Sb-Sb bonds, and both of them increase with decreasing Se content.Meanwhile, the formation of Se-Se bonds is limited. Finally, this induces theappearance of network demixing in main backbone, leading to degradation of thethermal and optical performance. The peaks at~2.4and~3.8in pair distributionfunctions of Ge-Sb-Se glasses represent the nearest-and the next-nearest neighborenvironments, respectively.②When Ge content is kept constant, all the density, the shear and thecompression elastic moduli, the glass transition temperature (Tg), the glass transitionenergy (Et) and fragility index (m) increase with increasing Sb content inGe12.5SbxSe87.5-x(x=5,10,15,20,25) glasses. However, the transmittance and theoptical bandgap decrease with increasing Sb content (Vis-NIR absorption wavelengthincreases with increasing Sb content)③In three groups of GexSb10Se90-x, GexSb15Se85-x, GexSb20Se80-xglasses, Sbcontent is kept constant, the density shows the "N" shape evolution with increasing Gecontent, there are two transition thresholds at MCN=2.4and the stoichiometriccomposition (the minimum) of Ge25Sb10Se65, Ge20.83Sb15Se64.17, Ge16.67Sb20Se63.33,respectively. All the shear elastic moduli, the compression elastic moduli and hardnessof Ge-Sb-Se glasses increase with increasing Ge content. Tg, the transmittance and theoptical bandgap first increase and then decrease with increasing Ge content, however,the refractive index and the Vis-NIR absorption wavelength first decrease and thenincrease with increasing Ge content, the extrema (the maxima or minima) appear at theGe25Sb10Se65, Ge20.83Sb15Se64.17, and Ge16.67Sb20Se63.33, respectively, which correspondto the chemically stoichiometric composition.④Comparing the Tgof the glasses with different compositions but the same MCN,the value of Tgis almost equal when MCN＜2.45, however, in the case of MCN>2.45,the network of glass is over-constrainted, the value of Tgshows a large difference. Theminima of the glass transition energy (Et) and fragility index (m) occur at MCN=2.4,indicating the best glass stability. Crystallization activation energy (Ec) increases rapidlyat around MCN=2.4, and saturation of crystallization appears after MCN=2.65. Thethermal stability and glass forming ability of Ge-Sb-Se glasses decrease with increasingMCN.⑤Taking all the parametes of structure, the elastic moduli, the hardness, the thetransmittance, the Vis-NIR absorption wavelength, the optical bandgap and therefractive index of Ge-Sb-Se glasses into account, the appropriate glasses with relatively stable structure and better mechanical and optical properties for theapplication in photonics such as the integrated nonlinear or advanced infrared opticaldevices should be in the composition range spanning from MCN=2.4to thestoichiometric composition, and taking Tg, Ec, Et, m, the thermal stability and glassforming ability into account, the appropriate glasses meet thermal requirements of thedevices should have a MCN of2.4.The results above provide great guiding significance and important applicationvalue for the preparation and selecting of Ge-Sb-Se chalcogenide glasses which havestable structure, good mechanical, thermal and optical properties.