Crystal growth and characterizations of quartz-like material: Gallium phosphate (GaPO4)

This investigation concerns GaPO4 crystal growth in phosphoric and sulphuric acid media by the slow heating and vertical reverse temperature gradient methods. Systematic study of growth parameters shows that the growth rate V-x is generally much greater than the other two, V-z and V-y. The most interesting result is the ability to produce GaPO4 epitaxy on large berlinite seeds in sulphuric acid and to use them for GaPO, crystal growth in phosphoric acid where the V-x/V-z ratio can be close to 1. As for alpha-quartz and berlinite, V-y growth rate being always very slow, the lengthening of these crystals in that direction is obtained by the use of several joined seeds accurately adjusted and spliced on a quartz plate. The epitaxial fit and the crystalline quality have been checked by X-ray topography. The OH content, determined by infrared and near infrared spectrometry, proves a lower OH concentration than in the case of berlinite when approximately the same crystal growth conditions are used. Piezoelectric characterizations of resonators have been suitable to specify the AT-cut position, its very promising piezoelectric properties with a high thermal stability and a Q factor are already nearly sufficient for applications. The most interesting properties of these crystals, the piezoelectric properties, are compared with those of other known crystals, quartz and berlinite, and related to their crystal structure distortions. The observed evolution allows the prediction of some interesting unknown characteristics for other quartz-like materials.