How to Cultured crystal

“Cultured crystal” Usually refers to “artificially grown crystals”：

Definitions and Overview

Artificially cultivated crystals are crystal materials with regular geometric shapes and specific physical and chemical properties that simulate the physical and chemical conditions of natural crystal formation by artificial means, and promote the arrangement of atoms, ions or molecules according to a specific lattice structure in a laboratory or factory environment. It covers many types, in addition to the aforementioned artificially cultivated quartz (crystal), it also includes artificially cultivated gemstone crystals, such as artificially cultivated rubies, sapphires, emeralds, etc., as well as functional crystals used in many fields such as industry, scientific research, etc., such as artificially cultivated silicon carbide, gallium nitride, etc.

Cultivation methods

• Melt Method:
  • Lifting method: It is often used to grow high-quality single crystals, such as artificially cultivated rubies and sapphires. The raw materials (such as alumina powder, etc., for rubies, chromium will be added as a coloring agent) into a high-temperature crucible heated and melted, and then the seed crystal is touched on the surface of the melt, and the seed crystal is slowly pulled upward, and the melt will gradually solidify and crystallize on the seed crystal, and continue to grow according to the lattice orientation of the seed crystal, and finally form a single crystal with large size and excellent crystal quality. This method produces crystal integrity and high optical homogeneity, which makes it widely used in optical fields where high-quality crystals are required, as well as in high-end gemstone manufacturing.
  • Flame melting method: After melting the raw material powder mainly through the high temperature generated by the hydrogen and oxygen flame, it is gradually solidified and crystallized on a special crystal seed, so as to form a crystal. This method is often used in synthetic corundum-like gemstones (including colorless corundum, colored corundum, etc.). The raw material powder is sprayed into the flame and melted through the powder feeding device, which has the advantages of relatively low cost, high production efficiency, and can quickly grow larger crystals; However, there may be certain stress and other defects inside the crystal, so it is mostly used in the production of gemstone jewelry that does not require extremely high crystal quality.
• Solution method:
  • Hydrothermal method: not only suitable for artificially cultivated quartz (crystal), but also quite effective for the growth of some other crystals, such as artificially cultivated emeralds, the raw materials containing beryllium, aluminum and other elements and mineralizers are put into the autoclave, in a high temperature and high pressure environment, these raw materials are dissolved and transmitted in the solution, and then crystallized and grown on the seed crystals, simulating the growth process of natural emeralds in a hydrothermal environment, and finally obtaining artificially cultivated emerald crystals. Its appearance and some properties are similar to those of natural emeralds, but some subtle differences can be found through professional gem identification methods, and are often used to make gemstone jewelry and as a sample for gemstone research.
  • Low temperature solution method: It is to use organic solvent or aqueous solution as a solvent at a relatively low temperature (generally lower than the boiling point of water) to dissolve the crystal raw materials, and precipitate the growth crystals by slowly evaporating the solvent and changing the temperature. The operating conditions of this method are relatively mild, and it is suitable for the growth of some crystals that are easy to decompose at high temperature or have special structural requirements, and is often used in some scientific research fields to synthesize new functional crystal materials.
• Gas phase method:
  • Chemical vapor deposition (CVD): used for example in the synthesis of diamonds (diamonds) and some semiconductor crystals (e.g. silicon nitride). The gaseous compounds containing the crystalline elements (for example, for diamond synthesis, methane and other carbon-containing gases are often mixed with hydrogen) are passed into the reaction chamber, and under the action of high temperature, plasma or catalyst, the gaseous substances undergo a chemical reaction, and the decomposed atoms are deposited on the substrate and crystallized to grow into crystals. This method can accurately control the number of growth layers and composition of the crystal, and is widely used in semiconductors, superhard materials and other fields, such as in the manufacture of some high-performance chips, high-quality semiconductor crystals synthesized by CVD technology are the key basic materials.

Cultivation environment and equipment requirements

• Environmental conditions:
  • Temperature control: Different cultivation methods and crystal types require precise temperature control. For example, the temperature of rubies grown by the pulling method needs to reach about 2000°C, and the temperature of crystals grown by hydrothermal method is generally in the range of 300°C – 600°C. Accurate temperature control can ensure that crystal atoms or molecules are arranged in an orderly manner according to the predetermined lattice structure, which has a significant impact on the crystal quality, so it is usually equipped with high-precision temperature sensors and automatic temperature control systems to control the temperature error within a very small range.
  • Pressure control (for some methods): Hydrothermal methods, chemical vapor deposition methods (under certain high-pressure reaction conditions), etc., require strict control of the pressure environment. The appropriate high pressure in the hydrothermal method can promote the raw materials to better dissolve and crystallize in the solution, and improper pressure is easy to cause crystal defects. Chemical vapor deposition facilitates the chemical reaction and atomic deposition of gaseous substances at specific high pressures, and the precise maintenance of pressure relies on professional pressure regulation and monitoring equipment to ensure that the pressure is stable around the set value.
  • Cleanliness and atmosphere control: For most artificially cultivated crystals, especially those used in high-precision fields such as electronics, optics, and scientific research, the cleanliness of the cultivation environment is extremely high, and it is necessary to prevent impurities from mixing and affecting the crystal performance. At the same time, some crystal growth requires a specific atmosphere environment, for example, when synthesizing some semiconductor crystals by CVD method, it is necessary to accurately control the proportion and purity of hydrogen, nitrogen and other gases in the reaction chamber, which requires the configuration of gas purification, flow control and atmosphere monitoring devices to ensure it.
• Equipment:
  • Furnace (for melt method): It needs to have the characteristics of high temperature resistance, uniform heating, and adjustable power to ensure that the raw material can be fully melted and the melt state is stable, which is conducive to crystal growth. For example, the furnace used in the lifting method should have a heating system that can keep the raw material in the crucible in a uniform melting state at high temperatures, so as to ensure the consistency of the quality of the crystals as they are lifted and grown from the melt.
  • Autoclave (key equipment for hydrothermal method): the material should be able to withstand high temperature and high pressure, and the internal structure design should be convenient for placing raw materials, mineralizers and seed crystals, etc., with good sealing performance to prevent solution leakage and pressure runaway. At the same time, it is equipped with perfect temperature and pressure sensing and control devices to achieve accurate control of the hydrothermal reaction environment.
  • Reaction chamber (main equipment for gas phase method): To create an environment that can accurately control gas flow, temperature, pressure and provide suitable reaction conditions, the internal substrate material selection is also critical, which will affect the quality of crystal deposition and growth, and is usually connected to various gas supply, purification, monitoring and control systems to ensure the smooth progress of the chemical vapor deposition process.

peculiarity

• High controllability of composition and structure: According to the specific application requirements, the type and content of elements contained in artificially cultivated crystals and the lattice structure of crystals can be accurately controlled, so as to obtain crystals with specific properties. For example, when cultivating gallium nitride crystals, by adjusting the types and proportions of doping elements, they can have different electrical properties to meet the requirements of different electronic devices for semiconductor materials.
• Good quality uniformity: Compared with the uneven quality of natural crystals affected by complex geological environment, artificially cultivated crystals often show high uniformity in size, purity, physical and chemical properties and other aspects under relatively stable growth conditions set by artificial cultivation, which is convenient for standardized industrial application and batch processing and production, which is particularly important in fields with strict requirements for material consistency such as the electronics industry.
• Mass production: As long as there are suitable equipment and process conditions, artificially cultivated crystals with the same specifications and similar properties can be manufactured in batches according to the established production process to meet the large-scale market demand. For example, in the production of artificially cultivated quartz for quartz crystal oscillators, a large number of crystal materials that meet the requirements can be stably supplied through an industrial-scale cultivation process.

Contrast with natural crystals

• Internal structure and features:
  • Inclusions differences: natural crystals will wrap around minerals, gases or liquids in the natural formation process, forming inclusions with irregular shape, size and distribution, which often become an important basis for identifying natural crystals; For example, in artificially cultivated sapphires, if the flame melting method is used, there may be tiny particle inclusions left due to the incomplete melting of the raw material powder, but their distribution is relatively more regular.
  • Difference in growth texture: The growth texture of natural crystals generally presents natural continuity and irregularity, and has the characteristics of bending and twisting in line with the natural growth law; The growth texture of artificially cultivated crystals sometimes shows more regular and regular characteristics, for example, the growth texture of crystals cultivated by the lifting method often extends neatly along the direction of the seed crystals, and the difference between the two in this regard can be distinguished by microscopic observation methods.
• In terms of physical and chemical properties:
  • Overall similarity: If the cultivated crystal and the natural crystal are of the same type (such as artificial ruby and natural ruby), their basic physical and chemical properties are similar, such as chemical composition (the main component of artificial cultivated ruby is also alumina and contains chromogenic elements chromium, etc.), hardness (the Mohs hardness of ruby is about 9, and artificial cultivation and natural are basically the same), density and other aspects are roughly the same.
  • Subtle differences: However, there are subtle differences between the two for some high-precision measurements or specific performance requirements. For example, in terms of optical properties, artificially cultivated gemstone crystals may achieve higher optical uniformity by optimizing cultivation conditions; In terms of electrical performance, artificially cultivated crystals for electronic components can achieve more stable and design-compliant performance with more precise process control, which is often difficult to achieve due to natural growth conditions.

Fields of application

• Jewelry industry: Artificially cultivated gemstone crystals, such as rubies, sapphires, emeralds, etc., have a beautiful appearance and are usually more affordable than natural gemstones of the same type, and are widely used to make various styles of rings, necklaces, earrings and other jewelry, to meet the needs of different consumers for beauty and decoration, but also to provide jewelry designers with more materials to choose from, to achieve a variety of design ideas.
• Optics: Many artificially cultivated crystals have excellent optical properties, such as artificially cultivated calcium fluoride crystals have good light transmittance, and are used as window materials in infrared optical instruments; Artificially cultivated titanium-sapphire crystals are important laser crystals, which can produce high-energy and high-frequency laser beams, which are used in many laser applications such as laser processing and laser medical treatment, which greatly promotes the development of optical technology and the performance improvement of related instruments and equipment.
• In the field of electronics industry: artificially cultivated crystals play a key role in electronic devices, such as the aforementioned artificially cultivated quartz is used in quartz crystal oscillators to ensure the stability of clock signals of electronic products; Artificially cultivated gallium nitride crystals are a new generation of semiconductor materials, which have shown unique advantages in the manufacture of electronic components such as high-brightness LED lamps and power amplifiers for 5G communications, helping the electronics industry continue to develop in the direction of high performance, miniaturization and multi-function.
• Scientific research field: artificially cultivated crystals provide ideal research materials for scientific research, researchers can customize crystals with specific properties according to experimental needs, such as synthesizing crystals with special magnetic properties and electrical properties, for exploring new physical phenomena, research and development of new materials and technologies, such as in the research of high-temperature superconducting materials, some artificially cultivated transition metal oxide crystals are important research objects, which are expected to promote breakthroughs in basic science and applied technology.

In short, artificially cultivated crystals play an indispensable role in many important fields with their unique advantages and diverse properties, and with the continuous progress of technology, their types are still being enriched and their application prospects are becoming more and more broad.