Swept crystals are crystals that have undergone a solid-state electrodiffusion purification process. Sweeping involves heating the crystal above 500 °C in a hydrogen-free atmosphere, with a voltage gradient of at least 1 kV/cm, for several hours (usually over 12). The migration of impurities and the gradual replacement of alkali metal ions with hydrogen (when swept in air) or electron holes (when swept in vacuum) causes a weak electric current through the crystal; decay of this current to a constant value signals the end of the process. The crystal is then left to cool, while the electric field is maintained. The impurities are concentrated at the cathode region of the crystal, which is cut off afterwards and discarded.Arthur Ballato et al. Method of sweeping quartz , Issue date: January 19, 1982/ Swept crystals have increased resistance to radiation, as the dose effects are dependent on the level of alkali metal impurities; they are suitable for use in devices exposed to ionizing radiation, e.g. for nuclear and space technology.Frequency Control|Teaching Resources . Ieee-uffc.org. Retrieved on 2010-02-08. Sweeping under vacuum at higher temperatures and higher field strengths yields yet more radiation-hard crystals.James Claude King Vacuum electrolysis of quartz , Issue date: Jan 13, 1976. The level and character of impurities can be measured by infrared spectroscopy.Infrared study of defects in alpha quartz caused by sweeping effects. authors.aps.org (April 1997). Retrieved on 2012-06-21. Quartz can be swept in both α and β phase; sweeping in β phase is faster, but the phase transition may induce twinning. Twinning can be mitigated by subjecting the crystal to compression stress in the X direction, or an AC or DC electric field along the X axis while the crystal cools through the phase transformation temperature region.
Swept crystals are crystals that have undergone a solid-state electrodiffusion purification process. Sweeping involves heating the crystal above 500 °C in a hydrogen-free atmosphere, with a voltage gradient of at least 1 kV/cm for several hours (usually over 12). The migration of impurities and the gradual replacement of alkali metal ions with hydrogen (when swept in air) or electron holes (when swept in vacuum) causes a weak electric current through the crystal; decay of this current to a constant value signals the end of the process. The crystal is then left to cool, while the electric field is maintained. The impurities are concentrated at the cathode region of the crystal, which is cut off afterwards and discarded.Arthur Ballato et al. Method of sweeping quartz , Issue date: January 19, 1982/ Swept crystals have increased resistance to radiation, as the dose effects are dependent on the level of alkali metal impurities; they are suitable for use in devices exposed to ionizing radiation, e.g. for nuclear and space technology.Frequency Control|Teaching Resources . Ieee-uffc.org. Retrieved on 2010-02-08. Sweeping under vacuum at higher temperatures and higher field strengths yields yet more radiation-hard crystals.James Claude King Vacuum electrolysis of quartz , Issue date: Jan 13, 1976. The level and character of impurities can be measured by infrared spectroscopy.Infrared study of defects in alpha quartz caused by sweeping effects. authors.aps.org (April 1997). Retrieved on 2012-06-21. Quartz can be swept in both α and β phase; sweeping in β phase is faster, but the phase transition may induce twinning. Twinning can be mitigated by subjecting the crystal to compres,sion stress in the X direction, or an AC or DC electric field along the X axis while the crystal cools through the phase transformation temperature region.