basic knowledge

Usually, the crystal is polyhedral, and sometimes some special textures can be seen, such as banded structure, sand-bell structure (growth cone), crystal face steps, spiral lines on crystal faces and so on.

2. Brief introduction of common crystal growth methods

(1) aqueous solution method

Aqueous solution method includes solvent evaporation method, isothermal method and temperature difference method. Its working principle is raw materials, distilled water, seeds, etc. According to the types of growing crystals, add them into a crystal incubator (Figure13-1); Heating the liquid in the bathtub to fully dissolve the raw materials in the crystal incubator, controlling the temperature to saturate the solution in the crystal incubator, and crystallizing and growing the solute on the surface of the seed crystal.

Figure 13- 1 schematic diagram of crystal growth by aqueous solution method

(According to Cong et al., 1980)

(2) Flame melting method

The working principle of flame melting method is to use the high temperature generated by hydrogen and oxygen flame to heat and melt the powder material shaken off by the oscillator, and the melted melt falls on the seed crystal at the top of the support. With the slow descent of the scaffold, the melt gradually crystallized into pear-shaped crystals (Figure 13-2). The technological process is: raw material purification → powder preparation → crystal growth → annealing treatment.

Figure 13-2 schematic diagram of crystal growth by flame melting method

(3) Hydrothermal method

Hydrothermal method includes isothermal method, oscillation method and temperature difference method. Among them, the working principle of temperature difference hydrothermal method is to add raw materials, mineralizers, seeds and so on. According to the type of growing crystal, put it into an autoclave (Figure13-3); The autoclave is sealed and heated in a heating furnace, so that a certain temperature difference is generated between the raw material dissolution zone and the crystal growth zone, which promotes the convection and diffusion of the solution in the autoclave, and the solute crystallizes and grows on the surface of the seed crystal.

Figure 13-3 Schematic diagram of hydrothermal crystal growth

(4) cosolvent method

The flux method includes spontaneous nucleation method and seed growth method. Its working principle is to melt the raw materials that make up the crystal in the flux with low melting point at high temperature to form a uniform saturated melt, and then to promote the crystal growth of the melt by slowly cooling or evaporating the flux at constant temperature (Figure 13-4).

Fig. 13-4 schematic diagram of crystal growth by co-solvent method

(According to Cong et al., 1980)