Gallium orthophosphate (GaPO4), has twice the sensitivity of quartz (SiO2) and tourmaline and the unparallel thermal stability of many piezoelectric properties. Therefore it is a very promising compound for sensor applications. Its intrinsically high electrical resistance enables the production of transducers that show excellent sensing behaviour in extremely high temperature and pressure. In combination with the inherent material rigidity, GaPO4 allows for excellent signal qualities in very compact designs Due to the lack of natural GaPO4 crystals, the GAPOGROWTH project cooperated with Piezocryst of Graz Austria to develop growing techniques for small and larger GaPO4 single crystals. This is currently the sole manufacturer of this outstanding material with an industrial production facility equipped with autoclaves specifically designed for the growth of GaPO4 crystals. Investigations and tests of different hydrothermal crystal growth strategies demonstrated the feasibility of producing single crystals suitable for the fabrication of square wafers. With the use very fine grains, the smallest samples were cut to a size of 1.24mm x 0.50mm x 0.25mm. Adaptation of grinding and polishing equipment helped to achieve excellent polished samples with a diameter up to 14mm and a thickness of 0.15mm. Moreover, specific methods for the chemical machining of the new materials that would allow the fabrication of microdevices have been developed by the GAPOGROWTH project partners.
Growth of large gapo4 single crystals and their use for special sensor applications
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