| Abstract: | The character of the α–β transition in crystals of natural and synthetic quartz has been studied by measuring the refractive index. The coexistence of two different crystallographic modifications over some temperature range has been established. The α–β phase transition is supposed to be attributed to the near-critical phase transitions. In synthetic quartz with Al and Fe structural impurity the α–β transition consists of two successive transitions. First the transition from the α-phase to an intermediate one takes place, then the intermediate phase is transformed into the β-Phase. Within a certain temperature range there exists only the intermediate phase. |
