Orthorhombic crystal system

The orthorhombic crystal system is one of the seven crystal systems in crystallography. It includes all point groups with three mutually perpendicular twofold rotation or rotary inversion axes. The orthorhombic crystal system is also known as rhombic crystal system. The term rhombic may however not be confused with rhombohedral.

Point groups

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

Grid system

The orthorhombic lattice system has the holohedry.

In the orthorhombic lattice system are grid axes in the direction of three mutually perpendicular axes of symmetry. For the length of the lattice axes is obtained, no further conditions. This results in:

For determining which axis a, b ​​or c, there is only the condition that a right-handed coordinate system to be built. In general, the axes are selected so that the Hermann- Mauguin symbol corresponds to the standard of the International Tables for Crystallography. With the Hermann- Mauguin symbols, the space groups can, however, with respect to each possible choice of axis describe. As this occurs frequently, there are in the International Tables a tabular overview of all the ways to describe a space group with an arbitrary choice of axis. Basically, it is therefore advisable to use in specifying the space group with the space group number, as it is thus easier to find.

Bravais lattice

Orthorhombic face-centered lattice: oF

In the orthorhombic crystal system, there are four Bravais lattice. In the standard setup, the b- centered lattice is not, and the a- centered lattice only in the point group. This is due to the fact that in this point group the grid system is basically set up so that the twofold axis is along the c - axis lattice. Therefore, it is not possible to place in all cases, the lattice axes so that only the c- centered lattice is used. The orthorhombic lattice system is abbreviated as o.

Description and physical properties of the orthorhombic point groups

For a description of the orthorhombic crystal classes in Hermann- Mauguin symbolism symmetry operations are given with respect to three predetermined directions ( directions of gaze ) in the grid system. As monoclinic corresponding to three directions of the views A ( <100> ), B ( < 010 >), and c lattice axis ( <001 > ). As all three lattice directions are symmetry directions, but there is also the Hermann- Mauguin symbol of three short information.

It is characteristic of the orthorhombic space groups that in the Hermann- Mauguin symbol Brief no 3, 4 or 6 occurs.

Wherein the information about the physical properties of "-" means not allowed and " " allowed due to the symmetry due to the symmetry. 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 orthorhombic crystallized chemical substances, see Category: orthorhombic crystal system