What Is a Crystal Structure?
The crystal has three-dimensional periodic arrangement of atoms, ions, and molecules in space as its most basic structural feature. Any crystal can always find a set of basic vectors corresponding to the three-dimensional periodicity and the corresponding unit cell. Therefore, the crystal structure can be regarded as a unit cell containing the same parallelepiped shape according to the front, back, and left. , Right, up, and down are a set of "juxtapositions" next to each other. In crystallography, the crystal structure can be expressed in the form of atomic discrete distribution, or in the form of continuous electron density function.
- Since the atom is not in
- Experiments have shown that heat must be exothermic when transitioning from a gaseous, liquid or amorphous state to a crystal. Conversely, heat must be absorbed when transitioning from a crystalline state to an amorphous, liquid, or gaseous state. It is shown that under the same thermodynamic conditions, the internal energy of crystals is the smallest compared with the same chemical composition of gas, liquid or amorphous. That is, under the same thermodynamic conditions, the crystals with the same chemical composition are more stable than the amorphous, and the amorphous is unstable. The latter has the tendency to spontaneously transform into crystals.
- The crystal has a fixed melting point. When the crystal is heated to a certain temperature, the crystal begins to melt, and the temperature is maintained during the melting process, and the temperature does not start to rise again until the crystal is completely melted. As shown in Figure 1-1-3: The melting point of quartz is 1470 ° C, and the melting point of silicon single crystal is 1420 ° C.
- Crystal structure