Gallium lanthanum sulfide glass

Last updated September 23, 2023

Gallium lanthanum sulfide glass is the name of a family of chalcogenide glasses, referred to as gallium lanthanum sulfide (Ga-La-S) glasses. They are mixtures of La₂S₃, La₂O₃, and Ga₂S₃, which form the basic glass with other glass modifiers added as needed. Gallium-lanthanum-sulfide glasses have a wide range of vitreous formation centered around a 70% Ga₂S₃ : 30% La₂S₃ mixture, and readily accept other modifier materials into their structure.^[1] This means that Ga-La-S composition can be adjusted to give a wide variety of optical and physical properties.

History and physical properties

The glass forming ability of gallium(III) sulfide and lanthanum sulfide was discovered in 1976 by Loireau-Lozac’h, Guittard, and Flahut.^[2]

Optically, Ga-La-S has a high refractive index, a transmission window covering most of the visible wavelengths and extending to about 10 µm and a low maximum phonon energy, approx. 450 cm⁻¹.

Thermally, the refractive index of Ga-La-S glasses has a strong temperature dependence and low thermal conductivity, which results in strong thermal lensing. However, the high glass transition temperature of Ga-La-S makes it resistant to thermal damage, it has good chemical durability and unlike many chalcogenides which are based on arsenic, its glass components are non-toxic.

A clear advantage over other chalcogenides is its high lanthanum content which allows excellent rare-earth solubility and dispersion of the ions in the glass matrix for active devices.^[3] Ga-La-S can exist in both glassy and crystalline phases,^[1] in a glassy phase, it is a semiconductor with a bandgap of 2.6 eV corresponding to a wavelength of 475 nm; consequently Ga-La-S glass takes a deep orange colour. As with all chalcogenides the phase of the bulk is determined by two key factors; the material composition and the rate at which the molten material is cooled. These variables can be controlled to manipulate the final phase of the material.

Chemistry

Figure 2. The covalent Ga2S3 crystalline network. Ga2S3 bond structure.jpg — Figure 2. The covalent Ga₂S₃ crystalline network.

The structure of Ga-La-S glass consists of Ga-S bonds, with a length of 0.226 nm, and La-S bonds of length 0.293 nm. It has been reported that the Ga-S bond lengths in the glassy state are identical to those in the crystalline state.^[5] Therefore, it is only necessary to change the bond angles and, thus, it is hypothesised that Ga-La-S has the potential to be a fast switching phase change memory material.

In the Ga₂S₃ crystal shown in (figure 2 below) it should be noticed that two out of three sulfur atoms (S1 and S2) are each bound to three gallium atoms. These sulfur atoms have two normal covalent bonds to two of the gallium atoms. The third Ga-S bond is dative or coordinate covalent (one of the atoms provides both electrons). The third sulfur atom, S3, is bound to just two gallium atoms and is thought to be a bridging atom. The average sulfur coordination number is greater than two; sulfide glasses usually have coordination numbers less than two. Experimentally, Ga₂S₃ has not been observed in a glassy state. There exists however a GaS₄ unit within the Ga-S crystal which has been noted as the glass former. The La-S bond is ionic and likely to be a network modifier. By adding an ionic sulfide to the crystal, like La₂S₃, it is possible to modify the crystalline Ga₂S₃ into a vitreous structure.

Of all the rare-earth sulfides, lanthanum gives the largest range of vitreous composites. The effect of adding an ionic sulfide modifier such as a La₂S₃ molecule to the crystal is to break one of the Ga-S dative bonds and replace it with a S²⁻ anion. This anion links the gallium atom such that its tetrahedral environment is not altered, but what was a tricoordinated S atom now becomes a dicoordinated bridging atom. This process creates a negative void which can then be filled by a La³⁺ cation. Electrically, the effect of adding La₂S₃ is to give the glass an essentially ionic character.^[5]

Manufacturing

For both the practical application and scientific study of chalcogenide glasses, glass purity is of utmost importance. Varying levels of trace impurities, even at levels of a few parts per million can alter the spectroscopic behavior of a glass. Similarly, impurities are a major concern for optical components. Impurities in the raw materials and hence in the resulting glass, contribute to the loss of power through an optical component, whether it is in the form of a long glass fiber or an infrared window. These impurities contribute to the optical loss through absorption and scattering as well as serving as nucleation sites for crystallization.

Although high purity raw elements are now commercially available, with 99.9999% purity routine for many metals, even this level of purity is often not sufficient, particularly for optical fiber applications.^[6] More of a concern are commercially available chalcogenide compounds such as germanium sulfide, gallium sulfide or arsenic sulfide. Although these may have been synthesized from high purity elements, the conversion process itself can readily introduce oxide, water or organic impurities. It is not unheard of to find for example, commercial gallium sulphide contaminated with 45% or more gallium oxide through incomplete reaction of the precursors during production.

The conventional method for producing chalcogenide glasses is through the use of sealed ampoule melting. In this technique the required glass precursor materials are sealed under vacuum in a silica ampoule, melted, and then quenched to form a glass within the ampoule. The requirement for the sealed atmosphere is dictated by the volatile nature of many of the precursors which if melted in open atmosphere can result in large compositional changes or complete removal of components with low vapour pressures. This process also has the effect of trapping any impurities in the precursors within the glass as thus the precursor purity limits the ultimate quality of the glass that is produced. In addition, impurities can be transferred to the glass from the ampoule walls.

The closed nature of the process leads to tightly controlled quality. In addition to the open and closed systems for glass melting, chalcogenide chemical vapour deposition is emerging as a method to produce high quality chalcogenide glass, in both thin film and bulk glass form.^[7]

Gallium lanthanum sulfide glasses use essentially non-volatile components La₂S₃, La₂O₃ and Ga₂S₃ to form the basic glass with glass modifiers added as needed. This allows melting in an open atmosphere, under a flowing inert gas, typically argon. Batches of the compounds are prepared in a nitrogen-purged glovebox, placed in a vitreous carbon crucible and transferred to a silica tube furnace in a sealed vessel. Melting is typically at 1150 °C for 24 hours.^[4]

The molten gallium sulfides fluxed the lanthanum compounds and incorporated them into the melt at temperatures much lower than their respective melting points. The viscosity of the melt is low enough, at approximately 1 poise, to allow full mixing without the need for a rocking furnace which is required for melting in an ampoule. The melt is normally quenched to glass by pushing it into a water cooled jacket. An advantage of melting in an open atmosphere is the ability of volatile impurities to boil off and be carried away, a significant advantage over sealed systems. For example, no SH- impurity is observed in the absorption spectra of Ga-La-S glasses, compared to very significant quantities in sulphide glasses melted by the sealed ampoule technique.

Related Research Articles

Gallium is a chemical element with the symbol Ga and atomic number 31. Discovered by the French chemist Paul-Émile Lecoq de Boisbaudran in 1875, gallium is in group 13 of the periodic table and is similar to the other metals of the group.

Glass is a non-crystalline solid that is often transparent, brittle and chemically inert. It has widespread practical, technological, and decorative use in, for example, window panes, tableware, and optics.

<span class="mw-page-title-main">Melting</span> Material phase change

Melting, or fusion, is a physical process that results in the phase transition of a substance from a solid to a liquid. This occurs when the internal energy of the solid increases, typically by the application of heat or pressure, which increases the substance's temperature to the melting point. At the melting point, the ordering of ions or molecules in the solid breaks down to a less ordered state, and the solid melts to become a liquid.

Zone melting is a group of similar methods of purifying crystals, in which a narrow region of a crystal is melted, and this molten zone is moved along the crystal. The molten region melts impure solid at its forward edge and leaves a wake of purer material solidified behind it as it moves through the ingot. The impurities concentrate in the melt, and are moved to one end of the ingot. Zone refining was invented by John Desmond Bernal and further developed by William G. Pfann in Bell Labs as a method to prepare high-purity materials, mainly semiconductors, for manufacturing transistors. Its first commercial use was in germanium, refined to one atom of impurity per ten billion, but the process can be extended to virtually any solute–solvent system having an appreciable concentration difference between solid and liquid phases at equilibrium. This process is also known as the float zone process, particularly in semiconductor materials processing.

Fused quartz,fused silica or quartz glass is a glass consisting of almost pure silica (silicon dioxide, SiO₂) in amorphous (non-crystalline) form. This differs from all other commercial glasses in which other ingredients are added which change the glasses' optical and physical properties, such as lowering the melt temperature. Fused quartz, therefore, has high working and melting temperatures, making it less desirable for most common applications.

Zinc sulfide is an inorganic compound with the chemical formula of ZnS. This is the main form of zinc found in nature, where it mainly occurs as the mineral sphalerite. Although this mineral is usually black because of various impurities, the pure material is white, and it is widely used as a pigment. In its dense synthetic form, zinc sulfide can be transparent, and it is used as a window for visible optics and infrared optics.

Arsenic trisulfide is the inorganic compound with the formula As₂S₃. It is a dark yellow solid that is insoluble in water. It also occurs as the mineral orpiment, which has been used as a pigment called King's yellow. It is produced in the analysis of arsenic compounds. It is a group V/VI, intrinsic p-type semiconductor and exhibits photo-induced phase-change properties.

<span class="mw-page-title-main">Boron trioxide</span> Chemical compound

Boron trioxide or diboron trioxide is the oxide of boron with the formula B₂O₃. It is a colorless transparent solid, almost always glassy (amorphous), which can be crystallized only with great difficulty. It is also called boric oxide or boria. It has many important industrial applications, chiefly in ceramics as a flux for glazes and enamels and in the production of glasses.

Chalcogenide glass is a glass containing one or more chalcogens. Such glasses are covalently bonded materials and may be classified as covalent network solids. Polonium is also a chalcogen but is not used because of its strong radioactivity. Chalcogenide materials behave rather differently from oxides, in particular their lower band gaps contribute to very dissimilar optical and electrical properties.

ZBLAN is the most stable, and consequently the most used, fluoride glass, a subcategory of the heavy metal fluoride glass (HMFG) group. Typically its composition is 53% ZrF₄, 20% BaF₂, 4% LaF₃, 3% AlF₃ and 20% NaF. ZBLAN is not a single material but rather has a spectrum of compositions, many of which are still untried. The biggest library in the world of ZBLAN glass compositions is currently owned by Le Verre Fluore, the oldest company working on HMFG technology. Other current ZBLAN fiber manufacturers are Thorlabs and KDD Fiberlabs. Hafnium fluoride is chemically similar to zirconium fluoride, and is sometimes used in place of it.

Lanthanum(III) oxide, also known as lanthana, chemical formula La₂O₃, is an inorganic compound containing the rare earth element lanthanum and oxygen. It is used in some ferroelectric materials, as a component of optical materials, and is a feedstock for certain catalysts, among other uses.

The indium chalcogenides include all compounds of indium with the chalcogen elements, oxygen, sulfur, selenium and tellurium. (Polonium is excluded as little is known about its compounds with indium). The best-characterised compounds are the In(III) and In(II) chalcogenides e.g. the sulfides In₂S₃ and InS.
This group of compounds has attracted a lot of research attention because they include semiconductors, photovoltaics and phase-change materials. In many applications indium chalcogenides are used as the basis of ternary and quaternary compounds such as indium tin oxide, ITO and copper indium gallium selenide, CIGS.

<span class="mw-page-title-main">Gallium(II) sulfide</span> Chemical compound

Gallium(II) sulfide, GaS, is a chemical compound of gallium and sulfur. The normal form of gallium(II) sulfide as made from the elements has a hexagonal layer structure containing Ga₂⁴⁺ units which have a Ga-Ga distance of 248pm. This layer structure is similar to GaTe, GaSe and InSe. An unusual metastable form, with a distorted wurtzite structure has been reported as being produced using MOCVD. The metal organic precursors were di-tert-butyl gallium dithiocarbamates, for example Ga^tBu₂(S₂CNMe₂) and this was deposited onto GaAs. The structure of the GaS produced in this way is presumably Ga²⁺ S²⁻.

<span class="mw-page-title-main">Fluoride glass</span> Class of glasses based on fluorides rather than oxides

Fluoride glass is a class of non-oxide optical glasses composed of fluorides of various metals. They can contain heavy metals such as zirconium, or be combined with lighter elements like aluminium and beryllium. These heavier elements cause the glass to have a transparency range extended into the infrared wavelength.

The structure of liquids, glasses and other non-crystalline solids is characterized by the absence of long-range order which defines crystalline materials. Liquids and amorphous solids do, however, possess a rich and varied array of short to medium range order, which originates from chemical bonding and related interactions. Metallic glasses, for example, are typically well described by the dense random packing of hard spheres, whereas covalent systems, such as silicate glasses, have sparsely packed, strongly bound, tetrahedral network structures. These very different structures result in materials with very different physical properties and applications.

Chalcogenide chemical vapour deposition is a proposed technology for depositing thin films of chalcogenides, i.e. materials derived from sulfides, selenides, and tellurides. Conventional CVD can be used to deposit films of most metals, many non-metallic elements as well as a large number of compounds including carbides, nitrides, oxides. CVD can be used to synthesize chalcogenide glasses.

Gallium(III) sulfide, Ga₂S₃, is a compound of sulfur and gallium, that is a semiconductor that has applications in electronics and photonics.

<span class="mw-page-title-main">I-III-VI semiconductors</span>

I-III-VI₂ semiconductors are solid semiconducting materials that contain three or more chemical elements belonging to groups I, III and VI (IUPAC groups 1/11, 13 and 16) of the periodic table. They usually involve two metals and one chalcogen. Some of these materials have a direct bandgap, E_g, of approximately 1.5 eV, which makes them efficient absorbers of sunlight and thus potential solar cell materials. A fourth element is often added to a I-III-VI₂ material to tune the bandgap for maximum solar cell efficiency. A representative example is copper indium gallium selenide (CuIn_xGa_(1–x)Se₂, E_g = 1.7–1.0 eV for x = 0–1), which is used in copper indium gallium selenide solar cells.

Tellurogallates are chemical compounds which contain anionic units of tellurium connected to gallium. They can be considered as gallates where tellurium substitutes for oxygen. Similar compounds include the thiogallates, selenogallates, telluroaluminates, telluroindates and thiostannates. They are in the category of chalcogenotrielates or more broadly tellurometallates or chalcogenometallates.

Optical glass refers to a quality of glass suitable for the manufacture of optical systems such as optical lenses, prisms or mirrors. Unlike window glass or crystal, whose formula is adapted to the desired aesthetic effect, optical glass contains additives designed to modify certain optical or mechanical properties of the glass: refractive index, dispersion, transmittance, thermal expansion and other parameters. Lenses produced for optical applications use a wide variety of materials, from silica and conventional borosilicates to elements such as germanium and fluorite, some of which are essential for glass transparency in areas other than the visible spectrum.

References

1 2 Flahaut, J.; Guittard M.; Loireau-Lozac'h, A.M. (1983). "Rare earth sulphide and oxysulphide glasses". Glass Technology. 24: 149–156.
↑ Loireau-Lozac'h, Anne-Marie; Guittard, Micheline; Flahaut, Jean (1976). "Verres formes par les sulfures L₂S₃ des terres rares avec le sulfure de gallium Ga₂S₃" [Glasses formed by rare earth sulphides La₂S₃ with gallium sulphide Ga₂S₃]. Materials Research Bulletin (in French). 11 (12): 1489–1496. doi:10.1016/0025-5408(76)90099-4. ISSN 0025-5408.
↑ Schweizer, T.; Hewak, D.W.; Samson, B.N.; Payne, D.N. (1997). "Spectroscopy of potential mid-infrared laser transitions in gallium lanthanum sulphide glass" (PDF). Journal of Luminescence. 72–74: 419–421. Bibcode:1997JLum...72..419S. doi:10.1016/s0022-2313(96)00387-0. ISSN 0022-2313.
1 2 Hewak, D.W.; Brady, D.; Curry, R.J.; Elliott, G.; Huang, C.C.; Hughes, M.; et al. (2010). "Chalcogenide glasses for photonics device applications". In Ganapathy, Senthil Murugan (ed.). Photonic glasses and glass-ceramics. Research Signpost. ISBN 978-81-308-0375-3.
1 2 Benazeth, S.; Tuilier, M.H.; Loireau-Lozac'h, A.M.; Dexpert, H.; Lagarde, P.; Flahaut, J. (1989). "An EXAFS structural approach of the lanthanum-gallium-sulfur glasses". Journal of Non-Crystalline Solids. 110 (1): 89–100. Bibcode:1989JNCS..110...89B. doi:10.1016/0022-3093(89)90186-5. ISSN 0022-3093.
↑ Sanghera, J.S.; Aggarwal, I.D., eds. (1998). Infrared Fiber Optics. Boca Raton, FL: CRC Press.
↑ Huang, C.C.; Hewak, D.W.; Badding, J.V. (2004). "Deposition and characterization of germanium sulphide glass planar waveguides". Optics Express. 12 (11): 2501–2505. Bibcode:2004OExpr..12.2501H. doi: 10.1364/opex.12.002501 . ISSN 1094-4087. PMID 19475087.

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[test-1] 1 2 Flahaut, J.; Guittard M.; Loireau-Lozac'h, A.M. (1983). "Rare earth sulphide and oxysulphide glasses". Glass Technology. 24: 149–156.

[2] Loireau-Lozac'h, Anne-Marie; Guittard, Micheline; Flahaut, Jean (1976). "Verres formes par les sulfures L₂S₃ des terres rares avec le sulfure de gallium Ga₂S₃" [Glasses formed by rare earth sulphides La₂S₃ with gallium sulphide Ga₂S₃]. Materials Research Bulletin (in French). 11 (12): 1489–1496. doi:10.1016/0025-5408(76)90099-4. ISSN 0025-5408.

[3] Schweizer, T.; Hewak, D.W.; Samson, B.N.; Payne, D.N. (1997). "Spectroscopy of potential mid-infrared laser transitions in gallium lanthanum sulphide glass" (PDF). Journal of Luminescence. 72–74: 419–421. Bibcode:1997JLum...72..419S. doi:10.1016/s0022-2313(96)00387-0. ISSN 0022-2313.

[glass-4] 1 2 Hewak, D.W.; Brady, D.; Curry, R.J.; Elliott, G.; Huang, C.C.; Hughes, M.; et al. (2010). "Chalcogenide glasses for photonics device applications". In Ganapathy, Senthil Murugan (ed.). Photonic glasses and glass-ceramics. Research Signpost. ISBN 978-81-308-0375-3.

[Loireau-5] 1 2 Benazeth, S.; Tuilier, M.H.; Loireau-Lozac'h, A.M.; Dexpert, H.; Lagarde, P.; Flahaut, J. (1989). "An EXAFS structural approach of the lanthanum-gallium-sulfur glasses". Journal of Non-Crystalline Solids. 110 (1): 89–100. Bibcode:1989JNCS..110...89B. doi:10.1016/0022-3093(89)90186-5. ISSN 0022-3093.

[6] Sanghera, J.S.; Aggarwal, I.D., eds. (1998). Infrared Fiber Optics. Boca Raton, FL: CRC Press.

[7] Huang, C.C.; Hewak, D.W.; Badding, J.V. (2004). "Deposition and characterization of germanium sulphide glass planar waveguides". Optics Express. 12 (11): 2501–2505. Bibcode:2004OExpr..12.2501H. doi: 10.1364/opex.12.002501 . ISSN 1094-4087. PMID 19475087.

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