Materials designed and engineered for technical applications must invariably meet or exceed multiple key specifications. Even if commercial realization is not intended, scientific interest is piqued if a challenging combination of properties is achieved, particularly if they are mutually exclusive for certain classes of materials. For example, the combination of mechanical toughness, chemical durability, and high thermal-shock resistance, with pore-free, smooth, aesthetically beautiful surfaces simultaneously realized in certain glasses that are crystallized in a controlled manner—glass-ceramics—have enabled two distinct, decades-long applications, cookware and flat cooktop panels. Other special glass-ceramic materials have been developed for electronic, photonic, dental, and biomedical applications. No other class of material could combine these properties in such an advantageous and economically feasible manner. This issue highlights six very different innovative applications of glass-ceramics, all of which owe their importance and continuing interest to “hard-to-combine” properties.

The design, properties, and applications of transparent glass-ceramics are reviewed. Interference effects in light scattering by transparent glass-ceramics are discussed. The scattering coefficient of transparent glass-ceramics is found to be significantly less than that for the case of independent Rayleigh scattering by nanocrystals; its wavelength dependence is qualitatively different. A reduction in interference effects achieved by precipitation of nanocrystals of different crystalline phases with different scattering properties results in glass-ceramics with high diffuse reflection. The origin of the low coefficient of thermal expansion of glass-ceramics is discussed based on the temperature dependence of the unit cell parameters of β-quartz solid solutions measured by in situ high-temperature x-ray diffraction. Transparent glass-ceramics doped with Co2+ and Ni2+ ions for thermal shock-resistant color filters, for broadband near-infrared (IR) optical amplifiers, and for passive Q-switching of eye-safe Er lasers are presented. Glass-ceramics with rare-earth titanates, titanates-zirconates, and niobates in dual roles of nucleators and active crystals are reviewed.

Glass-ceramics have gained considerable importance for applications in high-energy technology. Li- and Na-superionic ion-conducting ceramics find widespread use in lithium- and sodium-ion batteries as separators, solid electrolytes, and cathode materials. The ionic conductivity of these materials is influenced by crystal chemical parameters and can be further optimized via microstructural control using glass-ceramic processing. This article summarizes the most promising glass-ceramic material systems currently in use, detailing recent progress in understanding their structure–property–performance relationships. We also highlight the power and potential of solid-state nuclear magnetic resonance techniques for providing quantitative knowledge about structure, phase composition, and ion dynamics in these materials.

Many current technological applications are based on the electrical properties of materials. Among these, ferroelectricity, antiferroelectricity, paraelectricity, and resistivity are the most important to be studied and controlled. To overcome important drawbacks of sintered ceramics or single crystals with these characteristics, the preparation of glass-ceramics with these phases dispersed in a glass matrix is a possible solution. The formation of glass-ceramics shows great advantages—their properties (optical, electrical, mechanical, and chemical) can be controlled via the volume fraction of the dispersed active phase. Thus, the preparation and properties of glass-ceramics containing ferroelectric crystallites embedded in the glass matrix have received considerable interest. This article discusses state-of-the-art preparation of glass-ceramics with one important technological ferroelectric crystal, lithium niobate (LiNbO3). Since the preparation of LiNbO3 single crystals by traditional growth techniques is technically difficult and economically costly—and with dense ceramics, it is difficult to achieve a congruent composition—scientific research on the fabrication methods of inorganic glasses containing LiNbO3 crystallites is an important current topic.

Since the discovery of glass-ceramics by Stookey in the 1950s, there has been increasing demand for glass-ceramics with high strength and toughness for medical, structural, and consumer electronics markets. This article reviews recent developments in composition, microstructure, and mechanical properties of glass-ceramics, with an emphasis on their mechanical performance. It reveals that glass-ceramics with strength and toughness comparable to structural ceramics, such as Al2O3, have been successfully developed. Meanwhile, efforts are being devoted to creating glass-ceramics with further improved damage resistance. With inspiration from natural materials such as jade, baddeleyite, bone, and nacre, glass-ceramics with unique microstructures and properties have been obtained. Further progress is needed in the design of novel compositions, microstructures, and phase assemblages to activate multiple toughening mechanisms in glass-ceramics for significant improvements in strength and toughness.

Bioactive glasses and related bioactive glass-ceramics have been used for over three decades in biomedical applications such as bulk, particulate, or coatings materials. More recently, highly porous bioactive glass-ceramic scaffolds for bone-tissue engineering have also been developed from selected compositions of bioactive glasses. Current bioactive glass-ceramic scaffolds are characterized by an open porous network, high bioactivity, and mechanical properties similar to those of trabecular bone. This article reviews the latest achievements in the development of porous bioactive glass-ceramics intended for bone-tissue engineering applications, highlighting the fabrication technologies and scaffold properties. Improvements in the mechanical properties of bioactive glass-ceramic scaffolds exhibiting high bioactivity have been achieved by different approaches in the last 10 years. Relevant long-term in vivo studies are required to confirm the suitability of such bioactive glass-ceramic scaffolds in clinical applications.

Crystallization in glasses is usually considered to be a problem in the glass industry. However, controlled crystallization of glasses is an important prerequisite in the development of glass-ceramics with tailored useful properties. Similar boundary conditions apply when considering glass-ceramics for the immobilization of nuclear waste via vitrification. While uncontrolled crystallization in nuclear-waste glasses is problematic, chemically durable glass-ceramics with significantly high waste loadings can be produced with controlled crystallization of glasses. This article presents an overview of various aspects of nuclear-waste glasses where crystallization is either considered to be advantageous or problematic. The classification of glass-ceramic waste forms and strategies to design glass-ceramics for a given waste stream is discussed. Some open and relevant problems faced by researchers developing nuclear-waste glass-ceramics are also offered.