Gallium phosphate

Gallium orthophosphate ( GaPO4 or gallium ) is a colorless, crystallizing in the trigonal crystal system crystal with a hardness of 5.5 on the Mohs hardness scale. GaPO4 is isotypic to quartz, wherein the silicon atoms are alternately replaced by gallium, and phosphorus. Therefore, this crystal has almost the same properties, such as quartz, however, twice as large in the piezoelectric effect. Through this doubling arise for many technical applications advantages over quartz, such as a higher coupling constant for resonators.

Unlike quartz comes GaPO4 but not in the wild before, but must be produced synthetically. As with synthetic quartz breeding takes place hydrothermally.

Modifications

Has GaPO4 unlike quartz no α - β phase transition, so that the low temperature phase of the GaPO4 ( structure as α - quartz) to 970 ° C is stable and hence the physical properties of the crystal. At 970 ° C, however, finds a phase transformation takes in a cristobalite -like structure.

Structure

Similar to quartz is made ​​up of GaPO4 GaO4 and PO4 tetrahedra are tilted against each other something. The helical arrangement along the c - axis leads to optically right - and left-handed crystals ( enantiomorphism ).

Occurrence

Since GaPO4 not occur in nature, the crystal can only be produced synthetically. Currently GaPO4 is only produced by a company in Austria commercially.

Technical significance

Pressure sensors based on quartz must be cooled with water for applications at higher temperatures ( above 300 ° C). The desire to replace these comparatively large sensors with miniaturized uncooled, could be met first time in 1994, when it became possible to replace quartz piezoelectric pressure sensors by GaPO4.

GaPO4 has in addition to the substantially temperature- independent piezoelectric effect also excellent in electrical insulation properties at high temperatures. Likewise, there are temperature compensated crystal sections up to about 500 ° C and with quartz resonator qualities comparable. GaPO4 is used for high-temperature piezoelectric pressure sensors as well as in high-temperature - micro balances due to these material properties, in particular.