Tetragonal crystal system

The tetragonal crystal system is one of the seven crystal systems in crystallography. It includes all point groups that hold a fourfold rotation or rotary inversion axis in exactly one direction.

Point groups

The tetragonal crystal system includes the point groups. They form the tetragonal crystal family and can be described by the tetragonal lattice system.

Grid system

The tetragonal lattice system has the holohedry. As with the other farmers then crystal systems, the fourfold axis is placed in the direction of the c - axis lattice. As monoclinic the other two directions are perpendicular to the c -axis, and have - due to the c-axis Vierzähligkeit - furthermore also have the same length and are perpendicular to each other. Therefore, in this crystal system, only the two lattice constants a and c and it results in the following conditions:

Bravais lattice

In the tetragonal crystal system, there are two Bravais lattices, the primitive and body-centered. The face-centered Bravais lattice non-default installation, since this lattice can always be described by a centered symmetry, half as large unit cell. The body-centered lattice is obtained from the face-centered by the a-axis by 45 ° about the c -axis, and decreased by a factor.

Description and physical properties of the tetragonal point groups

For a description of the tetragonal crystal classes in Hermann- Mauguin symbolism symmetry operations with respect to a given direction ( viewing directions ) are given in the grid system. The direction of view of the first symbol is the c- axis ( <001 >) of the second symbol, the a- axis ( <100> ) and the third symbol, the surface diagonal of the c-plane (< 110> ).

Characteristic of the tetragonal space group is a 4 (4) in the first place, but not three ( 3) to the second position of the space group symbol.

For information on the physical properties means:

• "-" Because of the symmetry forbidden
• " " Due to the symmetry allowed.

About the magnitude of the effect can be made due to the symmetry no statement, but one can assume that this effect is never exactly disappear.

More tetragonal crystallizing chemical substances, see Category: Tetragonal crystal system