Crystallographic axes and quartz cut types

This explanation describes the crystallographic axes of a synthetic quartz crystal and the different types of cut (AT, BT and SC cut) used in the production of quartz crystals.

1. crystal structure of quartz

Quartz (SiO₂) crystallises in the trigonal crystal system. The structure consists of a network of SiO₄ tetrahedra arranged in a spiral along the Z-axis (also known as the c-axis).

2. crystallographic axes

A synthetic quartz crystal has the following main axes:
- a₁-, a₃-, a₃-axes (x-axes): In one plane, 120° to each other.
- Z-axis (c-axis): Corresponds to the optical axis.
- Y-axis: Electrical axis, perpendicular to the Z-axis.

3. AT section

The AT section is an inclined section (approx. 35.25°) against the Z axis in the X-Z plane. It is used to produce temperature-stable oscillating crystals. The oscillation takes place in the plate plane (planar mode).

4. other quartz cut types

A comparison of the most important cut types:

5. conclusion

The choice of cut significantly influences the properties of a quartz resonator. While the AT cut is widely used, the BT and especially the SC cut offer specialised advantages in terms of temperature compensation and mechanical stability.