Résumé
Hydrothermal crystal growth offers a complementary alternative to the conventionally used crystal growth techniques to synthesize new materials and grow bulk crystals for specific applications. These specialized techniques are often capable of growing crystals at temperatures well below their melting points and thus potentially offering routes to new phases or the growth of bulk crystals with less thermal strain. The hydrothermal process is utilized for growing a wide variety of crystals. Most of the electronic industry uses α‐Quartz due to its unique combination of piezoelectricity, high mechanical and chemical stability and very high mechanical coupling factor (Q) at resonance and is a low cost producing method, due to the matured crystal growth technology developed since 1970s. With a melting point of 1706°C and high chemical resistance, quartz crystals would be very difficult to form by either melt or flux techniques. Since cooling through the transition point at 573°C usually produces twins, any technique for production of single crystal must be done below this temperature due to the transition between α and β‐Quartz. Hydrothermal crystal growth helps in obtaining the crystals at temperatures lower than its transition temperature at high pressure. This paper presents hydrothermal growth of Ge doped SiO2 crystals for piezoelectric applications and the general principle of high hydrostatic pressure.