GB/T 39131-2020Terms and definitions of synthetic crystal materials (English PDF)

2.1 Crystals

A solid substance formed by periodic arrangement of internal particles (atoms, ions or molecules) in a three-dimensional space.

2.2 Natural crystal

Crystals formed naturally in nature.

2.3 Intraocular lens

Crystals prepared by artificial methods.

2.4 Single crystal

A substance with a continuous crystal structure.

2.5 Polycrystalline

A substance composed of two or more single crystals.

2.6 Crystal structure

A spatial arrangement formed by periodic repetition of the mass points in a crystal with a certain symmetry.

2.7 Unit cell

The smallest repeating unit that can reflect crystal symmetry and periodicity.

2.8 Crystal system

The system is divided according to the rotation axis contained in the crystal.

Note. According to the level of crystal symmetry, it can be divided into 7 crystal systems. equiaxed (cubic) crystal system, hexagonal crystal system, tetragonal crystal system, trigonal crystal system, orthorhombic (orthogonal) crystal system, monoclinic crystal system, and triclinic crystal system Crystal system.

2.9 Point group

The set of all symmetry operations of symmetry elements grouped together by one point.

Note. According to its symmetry elements, it is divided into 32 independent point groups.