Crystal Structures of Inorganic Materials

Abstract

Ceramics have high hardness and mechanical strength, excellent chemical and thermal stabilities, and particular electromagnetic and optical properties. Based on these unique properties, they have been widely used in our life, industry activities, and various environmental and energy fields. The durability of ceramics is derived from strong chemical bonding, that is, covalent and ionic bonds, and tight atomic packing. The electrical properties are dominated by crystal and electronic band structures and typically classified into insulator, dielectric, semiconductor, and metallic conductor. Typical covalent crystals are diamond, graphite, and hexagonal boron nitride (h-BN). Diamond, having 3D carbon network, is extremely hard, whereas graphite and h-BN are soft due to the hexagonal layer structure. Structural principle in ionic crystal is the alternate arrangement of cation and anion different in charge and size. The coordination configuration consisting of centered cation and surrounding anions is the elemental unit: for example, silica is constructed by SiO₄ tetrahedrons and titania by TiO₆ octahedrons. Lattice defects, such as vacancy and interstitial atom, provide a large influence on semiconductor and ionic conductor. Glass has a random network structure and has been applied in optical fields. Recent trend is the dimensional control of morphology from zero- to three-order. New functions of ceramics have been created using nanoparticle, nanofiber, nanosheet, hybrid, and nanoporous materials.