A compound is a pure substance composed of two or more different elements, and the different atoms that make up the compound must exist in a certain ratio. In other words, regardless of the source of the compound, it has a certain composition. Compounds can be represented by chemical formulas, which are composed of the symbols of the elements contained in the compound. For example, when writing the chemical formula of a binary compound composed of two elements, it is like naming its English name. The metal element is written first, and the less metallic one is second. For example, the chemical formula of sodium chloride is NaCl. When the number of atoms between different elements in a compound is unequal, the ratio can be written under the symbol and represented by a number. Our product types usually refer to inorganic compounds, mainly binary compounds such as: cadmium sulfide, bismuth telluride, cuprous oxide, etc., followed by binary and multi-component compounds, such as gallium aluminum arsenic, indium gallium arsenic phosphorus, phosphorus arsenic Gallium oxide, copper indium selenide and some rare earth compounds (such as SeN, YN, La2S3, etc.).