The crystals in which the internal particles are regularly and periodically arranged in three-dimensional space are called single crystals. The entire lattice of a single crystal is continuous and has important industrial applications. The entropy effect leads to imperfections in the solid microstructure, such as impurities, uneven strain, and crystal defects, so ideal single crystals of a certain size are extremely rare in nature and difficult to produce in the laboratory. On the other hand, in nature, the volume of the unideal single crystal is large. For example, some mineral feldspar can form single crystals (such as emerald, gypsum) that can reach several meters.
Due to its rich variety and superior performance, single crystal has a wide range of applications in the fields of electronic devices, aerospace, and machinery industries.
- Microelectronic devices: Single crystals are widely used in the field of microelectronic devices. As the third-generation semiconductor material, silicon carbide (SiC) has become the first choice of next-generation high-power device materials due to its significant advantages. Compared with silicon-based power semiconductor devices, SiC power devices have the advantages of small power loss, high heat resistance, superior performance, and the ability to be switched at high speeds. Power electronic devices made from SiC single crystals can operate in high voltage, high current, and high frequency environments. Diamond has a high hardness, a wide light transmission band and a high thermal conductivity, which can be used to make micro-lenses (including lenses, prisms, etc.) in optical instruments.
Figure 1. SiC single crystal
- Mechanical industry: There are many applications for single crystals in the mechanical industry. For example, a tool made of high-quality hexahedral diamond single crystal is not only easy to process, but also has a sharp blade, high quality, good wear resistance, and good comprehensive performance indicators. This tool is an indispensable tool for precision and ultra-precision machining and is often used in the machinery industry.
Figure 2. Tool made of diamond single crystal
From the perspective of bonding, single crystals can be divided into ionic crystals, atomic crystals, molecular crystals and metal crystals.
- Ionic crystals: Crystals formed by the combination of positive and negative ions or positive and negative ion groups through ionic bonding in a certain ratio are called ionic crystals.
- Atomic crystal: A crystal formed by the bonding of adjacent atoms only through strong covalent bonds is called an atomic crystal.
- Molecular crystal: A crystal formed by intermolecular forces between molecules is called a molecular crystal.
- Metal crystal: A crystal composed of metal cations and free electrons is called a metal crystal.
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- Bobo Yang. (2014), "A yellow emitting phosphor Dy:Bi4Si3O12 crystal for LED application." Materials Letters 135, 176-179.