Crystal growth history
The establishment of high-temperature crystallization as an independent trend is connected with the artificial ruby single crystal growth. The first trials were carried out in 1837 by the French chemist Mark Gauden. He succeeded in synthesizing 1 carat mass (0,2g.) ruby crystallites in a crucible covered with soot, by tempering mixture of potassium chromite with alumina at high temperature. In 1851 Senarmont observed formation of microscopic rhombohedrons by heating the solution of aluminum chloride in sealed tubes at above 350°C. In 1848 Ebelman obtained ruby crystallites by melting the mix of alumina and boric acid with potassium oxide. In 1877 Fremi and Fail synthesized corundum by melting aluminum oxide with lead oxide in a fire-clay crucible. Adding of chromic acids gave crystallites the ruby coloring. These crystallites found application as watch jewels. Fremi and Verneuil in 1887 obtained ruby by melting barium fluoride, calcium fluoride and cryolite, adding some potassium dioxide. However, practically a decade of search was required, in the result of which Augustus Verneuil succeeded in developing a technique of serial growing of 6g ruby single crystals. The outstanding contribution of A. Verneuil is that his method has not undergone principle changes for already more than 100 years, regardless of the number of attempts to modernize it.
The method of Verneuil permitted to carry out systematical investigations of high-temperature crystallization processes for the first time. A notion of defects was developed, which defined the real structure of single crystal. Actually on the basis of this technique, investigations on interrelation of the growth conditions and actual single crystal structure started being studied.
The demand to expand the range of synthetic single crystals promoted development of the new growth methods, principally different from the Verneuil method. Thus, in 1917 I. Czochralski suggested that crystals be pulled out from the melt being in the crucible. Appearance of this method allowed carrying out crystallization process under strictly controlled thermal-temporal conditions. It was actually due to Czochralski method that the crystallization processes in vacuum, as well as controlled neutral atmospheres turned out to be possible. Unlike the method of Verneuil the method of Czochralski underwent principle modifications. Thus, in 1926 S. Kyropoulos replaced the crystal pulling process from the melt with the directed crystallization of the melt by decreasing its temperature. Here, however, some complications occur in connection with withdrawal of the single crystal from the crucible. The problem was solved by M. I. Musatov, who proposed that single crystal should be pulled for the size excluding the single crystal contact with the crucible walls at the final stage of crystallization.
Revolutionary modifications to the Czochralski method were made by A.V.Stepanov, who proposed that single crystals should be pulled directly through the draw plate, which gives them a geometrical form .
Actually simultaneously with Czochralski Bridgman proposed the single crystal growth method in crucibles with a conical bottom. While moving such a crucible through the melting zone, in the conical part (due to the geometrical selection)exactly crystal growth conditions are being created. This method was improved by D.Stockbarger, who discovered a sufficient quality increase of single crystal by the rise of the temperature axial gradient within the crystallization zone. To realize this dependence Stockbarger installed a special thermal diaphragm in the crystallization zone, with the help of which he succeeded in increasing the value of the temperature axial gradient.
In 1964 Kh.S.Bagdasarov proposed a new method of refractory single crystal growth based on moving the crucible with the raw material (charge) and a single crystal seed in the horizontal direction. This method was developed to be employed for growth of large-size, Nd doped, high-perfect yttrium-aluminum garnet laser crystals. It turned out to be quite prospective for yttrium-erbium-aluminum garnet growth as well. With the help of the Bagdasarov method problems of synthesis of large and especially large plate-form refractory leucosapphire single crystals were solved.
