There are a great many crystals in the world. Over 6,000 types of naturally occurring crystals (i.e., minerals) are known, and if we include synthetic crystals, the number exceeds hundreds of thousands. Unfortunately, there is no universal method for classifying the structures (atomic arrangements) of all these crystals. However, for crystals with relatively simple compositions (consisting of about 1 to 3 types of elements), it is often the case that structures can be considered identical if we disregard the types of elements. Knowing these template structures (prototypes), which are common to many crystals, is extremely useful when studying crystals.
The Strukturbericht1 (hereafter SB) type is a classical classification scheme for crystal structures. In SB notation, the alphabetical letters shown in the table on the right indicate the chemical characteristics of the substance, and numbers are added to represent the prototypes of various crystal structures. This system worked well in the early days of crystal research, but as new structures were reported, the numbers kept increasing. Moreover, previously assigned numbers were sometimes corrected later, and the system gradually became unmanageable. The SB type symbols have not been updated since around 1990.
However, the lower-numbered SB symbols are still widely known and frequently used today. For example, rather than saying “the sodium chloride structure undergoes a phase transition to the cesium chloride structure,” it may be more compact and preferable to say “the B1 structure transitions to the B2 structure.” This page introduces the classification based on SB notation.
| Symbol | Chemical Composition |
|---|---|
| A | Elemental crystals |
| B | XY-type compounds |
| C | XY2-type compounds |
| D | XmYn-type compounds |
| E | Compounds containing two or more elements without molecular groups |
| F | Crystals with YR, YR2-type molecular groups |
| G | Crystals with YR3-type molecular groups |
| H | Crystals with YR4-type molecular groups |
| I | Crystals with YR6-type molecular groups |
| K | Crystals with complex molecular groups |
| L | Alloys |
| S | Silicates |
For detailed descriptions of each type, please see the following.