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ARTICLE
High Hardness Ge45As40Se15 Glasses Based on Ball-Milling and Chalcogenide Glasses Molded by Spark Plasma Sintering
1 Ningbo Institute of Oceanography, Ningbo, China
2 Key Laboratory of Impact and Safety Engineering, Ministry of Education, Ningbo University, Ningbo, China
3 Laboratory of Infrared Material and Devices & Key Laboratory of Photoelectric Materials and Devices of Zhejiang Province, Advanced Technology Research Institute, Ningbo University, Ningbo, China
4 Engineering Research Center for Advanced Infrared Photoelectric Materials and Devices of Zhejiang Province, Ningbo University, Ningbo, China
* Corresponding Author: Jierong Gu. Email:
Chalcogenide Letters 2026, 23(7), 4 https://doi.org/10.32604/cl.2026.086724
Received 04 June 2026; Accepted 06 July 2026; Issue published 07 August 2026
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In this work, Ge45As40Se15 chalcogenide glass was prepared using spark plasma sintering. This method synthesizes glass powder into blocks through a certain temperature and pressure, which is an effective densification and high-precision molding of infrared transparent blocks and lenses. Through X-ray diffraction (XRD) and differential scanning calorimetry analysis, we tracked the gradual evolution of the powder during ball milling and observed the existence of a glass transition temperature in the glass after powder hot pressing. This method can prepare components outside the conventional glass forming region with high hardness and infrared transmittance, providing a simple and economical synthetic approach for preparing chalcogenide glass materials with optical application potential.Keywords
Chalcogenide glasses are widely studied due to their unique properties, which is suitable for infrared transmission optical elements covering atmospheric windows. Chalcogenide glasses have good refractive index, thermal stability and infrared transmission [1,2,3]. It indicates that chalcogenide glass can serve as a potential candidate material in various fields such as infrared optical devices, optical fibers, waveguides, phase change memories, and biochemical sensors, etc. [4,5].
The common chalcogenide glasses on the current market includes As-Se, Ge-As-Se, Ge-Sb-Se and other glasses, which are usually prepared by traditional melting methods with high loss rates, even exceeding 30%. This greatly wastes raw materials and increases economic costs. Therefore, spark plasma sintering can effectively recycle and reuse the waste raw materials. In addition, the high-pressure and high-temperature environment can expand the glass forming region during this process, thus enabling the preparation of more glass that is difficult to prepare using traditional melting methods. Mathieu Hubert et al. prepared 80GeTe2–20Ga2Te3 glass outside the conventional glass forming region by combining mechanical synthesis and sintering [6,7,8,9,10,11].
At present, the hardness of chalcogenide glasses on the market is generally not high, and there is a disadvantage of being easily scratched [12,13,14,15]. The Vickers hardness of Ge10As40Se50 is only 171 kgf/mm2, the hardness of Ge28Sb12Se60 is 222 kgf/mm2 [16], the hardness of Ge33As12Se55 is 251 kgf/mm2, and the hardness of As2Se3 glass, which is the most commercially used chalcogenide glass in the world, is only 136 kgf/mm2 [17]. The hardness of these commonly used chalcogenide glasses is less than 300 kgf/mm2. Therefore, it is usually necessary to use Ge lenses as the outermost layer of lenses, but Ge materials are expensive and their performance decreases in high-temperature environments. Chalcogenide glasses based on As, Se, and Ge have a large glass forming region. Ge has a high coordination number (CN) of 4, as has a CN of 3, and Se has a CN of 2. Ge-As-Se glass can increase its mean coordination number and achieve higher hardness by adjusting the proportion of elements, which can effectively improve the problem of insufficient strength of chalcogenide glass and increase its application range [18,19].
This study is dedicated to a promising high hardness Ge-As-Se chalcogenide glass, and utilizes the highly coordinated element Ge to enhance the glass network structure. We prepared of a bulk material with a composition of Ge45As40Se15 chalcogenide glass by combining mechanical synthesis and spark plasma sintering, then investigated the changes in parameters such as glass transition temperature and transmittance of the glass. In addition, XRD spectroscopy and Raman spectroscopy were used to analyze the changes in the internal structure of the glass.
By employing the mechanical milling, amorphous Ge45As40Se15 powder was synthesized withusing high-purity germanium (5 N), arsenic (5 N), and selenium (5 N) as raw materials. This component is outside the conventional glass-forming region, as shown in Fig. 1. The mechanical milling was performed with a planetary ball mill (Pulverisette 5 Premium, Germany). Raw materials of 5 N purity were put in a 125 mL WC bowl with 10 WC balls of a diameter of 20 mm. A ball:powder mass ratio of 10:1 was used. Rotations at 400 rpm for 30 min and 30 min pauses were alternated for several hours. The powder obtained after mechanical grinding was characterized by XRD and DSC, and then 4 g of the powder was placed in a mold with a diameter of 20 mm for sintering. The glasses were sintered by spark plasma sintering (LABOX-1575F SPS, SINTERLAND Inc., Japan). The powder (Ge45As40Se15) were heated up to 770 K (50 K above Tg) under a pressure of 35 MPa for 3 min under vacuum (10−2 Pa).
Hardness was determined using a Vickers hardness tester (MH-30, Hengyi Co., China) on an average of 10 measures, with a charge of 50 g for 5 s. FTIR spectra were obtained using Nicolet 380 FTIR from 2.5 μm to 25 μm. Utilizing the D2 Phaser diffractometer manufactured by Bruker (Germany), X-ray diffraction (XRD) patterns were recorded employing CuKα radiation with a step increment of 0.016°, and the test range was from 10° to 70°. The microscopic morphology of the sample was investigated utilizing scanning electron microscopy (SEM, Tescan VEGA 3 SBH). Thermal analysis was measured by a differential scanning calorimeter (DSC, TAQ2000, USA) by heating in a sealed aluminum pan at a rate of 10°C/min under N2 atmosphere to obtain glass transition temperature Tg, sample mass was 10 mg, test temperature is from 323 K to 850 K. All the measurements were performed at room temperature.
Figure 1: Glass forming domain of Ge-As-Se system [18].
The X-ray diffraction (XRD) pattern of the Ge45As40Se15 glass is presented in Fig. 2, XRD can observe whether there is crystallization in the sample to a certain extent [20]. As shown in Fig. 2a, the XRD patterns of powders obtained at different ball milling times are presented. Multiple sharp diffraction peaks can be observed in the XRD patterns of powders with milling durations of 8, 16, and 32 h, respectively. This diffraction peak belongs to the Ge crystal phase and comes from the raw material of crystalline Ge. When the milling time reaches 48 h, the diffraction peak of the XRD is relatively weak. When the milling time is extended to 64 h, the diffraction peak of crystalline Ge disappears, indicating that the ground powder has transformed into an amorphous state. When the milling time is 80 h and 96 h, the XRD curve still does not show any diffraction peaks. Subsequently, the powders with milling times of 64 h, 80 h, and 96 h are compressed and sintered using SPS equipment, and the obtained glasses are subjected to XRD testing, as shown in Fig. 2b, and no diffraction peaks were observed in the XRD curves.
Figure 2: (a) The XRD curves of the powders with various milling duration of 8–96 h, (b) XRD curves of SPS-64h, SPS-80h and SPS-96h glass samples.
3.2 Surface Morphology Analysis
To further confirm whether microcrystals exist in the glass samples, the micro-morphology was obtained using SEM. The scanning electron microscope surface map of SPS-64h glass, SPS-80h glass and SPS-96h glass are observed in Fig. 3. It can be seen that these glass surfaces have no obvious microcrystals. However, it was also observed that as the milling time increased, more pores appeared in the glass. This is because during the milling process, there is a steady state time for the powder particles. Within the steady state time, as the ball milling time increases, the particle size of the powder decreases and the density of the sintered glass also increases. However, beyond the steady state time, pores appear, which in turn reduces the density of the sintered glass.
Figure 3: SEM images of (a) SPS-64h, (b) SPS-80h, (c) SPS-96h.
3.3 Thermal Properties Analysis
Fig. 4 shows typical DSC curves of glass samples. It can be observed that the transition temperatures and crystallization temperatures of SPS-64h glass, SPS-80h glass and SPS-96h glass are essentially identical. It can be observed that the particle size of the powder does not affect the transition temperature and crystallization temperature of the glass formed by hot pressing. Moreover, the transition temperature of the Ge45As40Se15 glass is as high as 717.9 K, whereas the transition temperature of the commonly used As2Se3 glass is only 455 K.
Mean coordination number (MCN) can be used to describe the internal structure of glass network, and the formula is:
Figure 4: The DSC thermal tracking curves of SPS-64h, SPS-80h and SPS-96h glass samples.
The IR transmission spectra of SPS-64h glass, SPS-80h glass and SPS-96h glass samples are shown in Fig. 5. Although the raw material configuration is completed in a vacuum glove box, the glass sample still has a relatively large absorption peak due to the long grinding time, during which air enters the WC bowl. The absorption peak at the wavelength of 6–9 μm is As-O and Ge-O. The absorption peak at the wavelength of 9–15 μm is As-O, Se-O and Ge-O [21]. It can be observed that as the grinding time increases, the transmittance gradually decreases, with SPS-64h glass having the highest transmittance among the three samples, reaching 51%. Impurities and pores are important factors affecting the transmittance of glass. As the ball milling time increases, the powder becomes finer, resulting in an increase in internal pores in the glass, which is the main factor leading to a decrease in glass transmittance.
Figure 5: IR transmission spectra of SPS-64h, SPS-80h and SPS-96h glass samples.
The typical Raman spectra of the glasses are shown in Fig. 6. The strongest band at 225 cm−1 in As2Se3 spectra, is ascribed to AsSe3/2 pyramidal units. As can be seen, with the increase of Ge content, the peak at 225 cm−1 disappears. This is because the Ge-Se bonding strength is 49.42 kcal/mol, while the As-Se bonding strength is only 41.69 kcal/mol. The strongest band at 190 cm−1 is ascribed to Ge-Se vibrations in [GeSe4] tetrahedrons. The strongest band at 175 cm−1 is ascribed to Ge-Ge vibrations in [Se3Ge-GeSe3] structural units [22,23,24]. From Fig. 7, it can be observed that as the Ge content further increases, the number of Ge-Ge homopolar bonds increases, resulting in a stronger peak at 175 cm−1.
Figure 6: Raman spectra of the SPS-64h, Ge33As12Se55 and As2Se3 glass samples.
Figure 7: Schematic diagram of how Ge addition crosslinks As-Se structure.
In this study, we successfully prepared bulk Ge45As40Se15 chalcogenide glass outside the conventional glass forming region using mechanical alloying method and spark plasma sintering. After 64 h of ball milling, the powder was completely vitrified, and the glass prepared by SPS had a maximum infrared transmittance of 51% and a Vickers hardness of 351.1 kgf/mm2. As the ball milling time further increases, the glass properties degrade, so choosing a suitable ball milling time is important. The simple and economical technique of mechanical synthesis combined with spark plasma sintering proposed in this study has opened up a new way to prepare chalcogenide glass components that cannot be prepared by traditional melting/quenching methods.
Acknowledgement:
Funding Statement: This work is supported by the National Natural Science Foundation of China (Grant No. 62075110), the Key R&D program of Zhejiang Province, China (Grant No. 2021C01025), the project of Key Laboratory of Impact and Safety Engineering, Ministry of Education (Ningbo University, CJ202506), and Joint Funds of the National Natural Science Foundation of China (U21A2056).
Author Contributions: The authors confirm contribution to the paper as follows: conceptualization, Xiang Shen; sample preparation, Jierong Gu; investigation and device design, Tiefeng Xu; XRD analysis and Raman analysis, Zijun Liu; DSC analysis, Licheng Hua; optical measurements, Shuangquan Xie. All authors reviewed and approved the final version of the manuscript.
Availability of Data and Materials: The data supporting the findings of this study are available from the corresponding author upon reasonable request.
Ethics Approval: Not applicable.
Conflicts of Interest: The authors declare no conflicts of interest.
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Copyright © 2026 The Author(s). Published by Tech Science Press.This work is licensed under a Creative Commons Attribution 4.0 International License , which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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