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Synthetic quartz crystals are grown in a high-temperature and high-pressure atmosphere using the fact that the solubility of quartz crystals in an alkaline solution differs depending on the temperature (more quartz crystals dissolve at higher temperatures). They are grown using the so-called hydrothermal synthesis method.

The growth furnace is a pressure vessel called an autoclave. The autoclave is filled with an alkaline solution such as Na₂CO₃ or NaOH and the temperature is raised to grow the crystals in a supercritical state. The raw materials dissolved under a high temperature and pressure shift from the bottom to the top of the autoclave due to convection in the solution by maintaining the top of it at a lower temperature than the bottom. The raw materials then deposit on the seed crystals to lead to the growth of the synthetic quartz crystals. Adjusting the growth conditions and the orientation and dimensions of the seed crystals depending on the application grows synthetic crystals with different shapes, dimensions, and characteristics. Synthetic quartz crystals grown under sufficient management have uniform quality with controlled shapes and dimensions.

Low-temperature quartz crystals (α-Quartz) are used in quartz devices. When melted and cooled under normal pressure, various SiO₂ crystals are generated. Therefore, it is necessary to grow quartz crystals under high-temperature and high-pressure conditions with an autoclave. It has been found that the crystal structure of quartz crystals easily changes at the boundary of 573°C. Accordingly, it is necessary to take great care not to exceed 573°C when handling quartz crystals.

The quality standards for synthetic quartz crystals are JIS-C6704 and IEC 60758.

It is known that crystal defects (linear defects and dislocations, etc.) become easier to identify through etching. This characteristic is used to standardize the number of tunnel-like cavities that appear when synthetic quartz crystals are etched.

This indicator stipulates the size and quantity of foreign substances contained in crystals. Typical foreign substances are fine crystals such as acmite (NaFe(SiO₃)₂) caused by iron (Fe), the material of the inner wall of the autoclave, and emeleusite (Li₂Na₄Fe₂Si₁₂O₃₀).

When defects are present in quartz crystals, OH groups form at the site of those defects. These OH groups absorb light in a specific infrared region. As the number of crystal defects increases, so does the number of OH groups. Accordingly, the amount of infrared absorption also rises. Meanwhile, crystal defects affect the characteristics of quartz crystal devices. The Q value is used as an indicator of that. This indictor relating the Q value to crystal defects is the infrared absorption coefficient (rate).

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