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Glass-ceramics are inorganic, non-metallic materials obtained by controlled crystallization of glasses through different processing routes; they contain at least one functional crystalline phase together with a residual glass, and the crystallized fraction may range from trace levels to nearly complete crystallization. Transparent glass-ceramics (TGCs) constitute the optically transparent subset of this class and combine a controlled crystalline microstructure with a residual amorphous matrix. Their transparency distinguishes them from conventional opaque glass-ceramics and is achieved by minimizing light scattering through careful control of crystallite size, volume fraction, spatial distribution, and refractive-index mismatch between the crystalline and glassy phases. Unlike conventional sintered ceramics, TGCs retain many of the processing advantages of glass while incorporating crystalline phases that can enhance mechanical, thermal, optical, or functional properties. Depending on their composition and microstructure, TGCs may exhibit improved hardness, fracture toughness, thermal stability, chemical durability, luminescence, nonlinear optical response, or ion-exchange strengthening capability. These features make TGCs attractive for applications requiring both optical clarity and advanced performance, including protective cover glass, transparent armour, precision optical substrates, laser and photonic components, optical sensors, and multifunctional host materials for rare-earth ions and nanoparticles.
- glass-ceramics
- glass crystallization
- ion exchange
- fracture toughness
- hardness
- crystal structure
- microstructure
- spodumene
- spinel
- cordierite
In this review, the terminology follows the updated definition of glass-ceramics proposed by Deubener et al. [1]. The emergence of glass-ceramics as a distinct class of materials is associated with two largely independent lines of scientific and technological development. In the United States, S. Donald Stookey at Corning Glass Works discovered in the late 1950s that a lithium-silicate-based photosensitive glass, when accidentally overheated, transformed into a remarkably strong, opaque white partially crystalline material rather than simply deforming as expected. This observation led to the development and commercialization of Pyroceram® and demonstrated that controlled crystallization of glass could produce materials with mechanical properties far superior to those of the parent glass [2]. In parallel, in the Soviet Union, Isaak I. Kitaigorodskii developed and systematized the concept of glass-crystalline materials under the term “sitalls” (Russian: cитaллы), a neologism derived from the Russian words cтeклo (“glass”) and кpиcтaлл (“crystal”). His work emphasized the deliberate formation of crystalline phases within a glassy matrix and promoted the use of such materials in construction, chemical engineering, and electrical insulation [3]. By the mid-1960s, these converging developments had established glass-ceramics as a new family of engineering materials, combining the formability of glass with the hardness, strength, and thermal stability of crystalline ceramics.
A decisive advance occurred when the Schott company developed ZERODUR®, a lithium aluminosilicate (LAS) glass-ceramic whose β-quartz solid-solution nanocrystals exhibit a negative coefficient of thermal expansion (CTE) that, when combined with the positive CTE of the residual glass, yields a bulk CTE approaching zero (<±0.05 × 10−6 K−1). This property made ZERODUR the material of choice for telescope mirror substrates, ring-laser gyroscopes, and, more recently, extreme-ultraviolet lithography stages, applications where sub-nanometre dimensional stability is paramount [4]. The optical quality required for these precision components highlighted a critical insight: transparency in glass-ceramics is not merely a cosmetic attribute but a quantitative indicator that the crystallite dimensions and the refractive-index mismatch between crystals and matrix have been kept below the thresholds set by Rayleigh and Mie scattering theory [5][6].
The past two decades have witnessed a dramatic resurgence of interest in transparent glass-ceramics (TGCs), driven predominantly by the consumer-electronics industry. Corning’s Gorilla Glass Ceramic 2 illustrates the commercial availability of transparent, ion-exchange-strengthenable glass-ceramic cover materials. In Corning laboratory tests, 0.6 mm specimens survived face drops from up to 1.0 m onto a surface replicating concrete, whereas competitive lithium aluminosilicate cover glasses typically failed at 0.5 m or less [7]. This qualified commercial example demonstrates the potential of TGCs to combine ceramic-like damage resistance with scalable glass-forming processes.
From a scientific perspective, the appeal of TGCs lies in the synergistic interplay between the glassy matrix and the crystalline phases [8]. Such phases can contribute hardness, elastic-modulus enhancement, crack deflection, and tailored thermal expansion, while the continuous glassy phase preserves optical isotropy, enables near-net-shape forming, and, crucially, provides a medium amenable to alkali-ion-exchange strengthening—a post-processing step that introduces a compressive stress layer of several hundred megapascals into the surface [5][9][10]. Crystallization can, however, compromise transparency when the resulting microstructure produces appreciable optical scattering. No single crystal-size threshold is universal: transparency depends jointly on crystallite size and size distribution, crystal volume fraction, refractive-index mismatch between the crystalline and residual glass phases, crystallographic anisotropy and birefringence, and specimen thickness. Thus, crystals larger than λ/20 may remain compatible with high transparency when Δn is very small, whereas even finer crystals can cause substantial losses at high volume fractions or large index contrast [5][11].
Recent review articles have comprehensively surveyed glass-ceramic science, from the recent comprehensive survey by Höland, Beall and Smith [2] to specialized monographs on transparent variants [5] and commercial trajectories [9]. The present entry aims to provide a concise yet comprehensive overview of the field of transparent glass-ceramics with particular emphasis on (i) the physico-chemical fundamentals governing transparency retention during crystallization; (ii) the major oxide glass-ceramic families—LAS, MAS, and ZAS—together with emerging compositions; (iii) mechanical property enhancement via nanocrystallization and ion exchange; (iv) the growing role of computational methods and machine learning in accelerating composition design; and (v) current and prospective applications. Throughout, the discussion highlights the tension inherent in TGC design: maximizing the volume fraction and size of the crystalline phase (for mechanical benefit) while remaining below the optical scattering threshold (for transparency).
References
- Deubener, J.; Allix, M.; Davis, M.J.; Durán, A.; Höche, T.; Honma, T.; Komatsu, T.; Krüger, S.; Mitra, I.; Müller, R.; et al. Updated definition of glass-ceramics. J. Non-Cryst. Solids 2018, 501, 3–10.
- Höland, W.; Beall, G.H.; Smith, C.M. Glass-ceramics: From ideas to products. J. Am. Ceram. Soc. 2025, 108, e20086.
- Montazerian, M. Isaak Il’ich Kitaigorodskii and the evolution of glass-ceramics. Am. Ceram. Soc. Bull. 2024, 103, 36–38.
- Mitra, I. ZERODUR: A glass-ceramic material enabling optical technologies. Opt. Mater. Express. 2022, 12, 3563–3576.
- Liu, X.; Zhou, J.; Zhou, S.; Yue, Y.; Qiu, J. Transparent glass-ceramics functionalized by dispersed crystals. Prog. Mater. Sci. 2018, 97, 38–96.
- Montazerian, M.; Zanotto, E.D. Nucleation, Growth, and Crystallization in Oxide Glass-formers. A Current Perspective. Rev. Mineral. Geochem. 2022, 87, 405–429.
- Corning® Gorilla® Glass Ceramic 2. Product Information Sheet; Corning Incorporated: Corning, NY, USA, 2025.
- Shakhgildyan, G.Y.; Xu, X.; Ojovan, M.I. Synergy in Polyphase Materials—Harnessing the Power of Glass and Ceramics. Materials 2026, 19, 478.
- Beall, G.H.; Comte, M.; Dejneka, M.J.; Marques, P.; Pradeau, P.; Smith, C. Ion-Exchange in Glass-Ceramics. Front. Mater. 2016, 3, 41.
- Seidel, S.; Dittmer, M.; Höland, W.; Rüssel, C. High-strength, translucent glass-ceramics in the system MgO-ZnO-Al2O3 -SiO2 -ZrO2. J. Eur. Ceram. Soc. 2017, 37, 2685–2694.
- Tick, P.A.; Borrelli, N.F.; Reaney, I.M. The relationship between structure and transparency in glass-ceramic materials. Opt. Mater. 2000, 15, 81–91.
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