LATTICE-DEFECTS AND MECHANICAL-BEHAVIOR OF QUARTZ SIO2

Quartz has the chemical composition SiO2. It is an abundant mineral in the Earth crust and its mechanical properties govern the theological behaviour of a number of crustal rocks. Quartz is also a material wide ly used in industry (resonators, filters...) owing to its remarkable p iezoelectric properties. Very small amounts of water in the quartz lat tice dramatically affect its mechanical properties. The mechanical str ength of ''wet'' quartz is at least 10 times lower than that of ''dry' ' quartz. This effect of water on quartz has been called hydrolytic we akening. The piezoelectric performances of resonators are also dramati cally reduced by the presence of amounts of water as small as [H]/[SI] approximate to 300 at. ppm. In order to get better performances, crys tal growers have investigated the grown-in lattice defects (dislocatio ns, twins, occurrence of water and other chemical impurities) and thei r influence on piezoelectric performances. The community of mineral ph ysicists have also investigated the lattice defects in quartz, especia lly dislocations, and the physical factors influencing their mobility. They have also investigated the behaviour of quartz under extreme dyn amic pressure; this situation corresponds to shock waves generated by the impact of meteorites on the Earth's surface. The aim of this artic le is to review the mechanical behaviour of quartz under various therm omechanical conditions and the role of the impurity ''water'' on the r elevant physical properties of quartz.