Crystal Growth

Crystal growth from high temperature solutions

Use of molten salts for dissolving chemicals and metals is widely known. Controlled cooling of the solutions leads to the crystallization of the solute. Crystals are also grown from molten solutions by top seeding and pulling the seed and simultaneously cooling the solution. This method has been employed for the growth of YBa2Cu3O6+d. Facilities are available in our laboratory to grown crystals both by the slow cooling and top-seeding. Vertical furnaces with alumina and mullite muffles provide the desired temperatures. Kanthal wire winding is used for furnaces operating upto 1200 °C. 2-4 SiC heating elements are used to provide upto 1350 °C intermittently and 1300 °C continuously in a short (2-5 cm) hot zone. Crucible and seed could be rotated and translated using slides mounted co-axially on sturdy stands that have been designed and built in house. This facilitates flexibility in operation and modification. For example simple sealing of the crystal growing chamber was possible to grow crystals in a positive atmosphere of oxygen. Molten salt sealing of the crucible was also possible to prevent rapid oxidation and evaporation of Cu form the crystals. Arrangements employed in these techniques are shown in the following figures.

Fig. 1 SiC heating element furnace to grow crystals from high temperature solutions in the range 1200-1350 °C. The vapors from the solutions are collected in a quartz scrubber tube placed above the furnace.

Fig. 2 The temperature profile of the SiC element furnace (a) is compared with a conventional wire-wound furnace 9b). The profiles are very close even though only two SiC elements are used. Corresponding photographs are given below.

Super Kanthal Crystal Growing and Annealing Furnace for 1600 °C Operation

Fig. 3 Super Kanthal heating element furnace for crystal growth and annealing at 1400-1600 °C. the photograph of the furnace with the leads exposed.

A furnace was designed and constructed for crystal growth and annealing of small volumes (10-50 cc) at high temperatures in the range 1200-1600 °C in air as well as protective atmospheres. This is presently used for mostly annealing crystals and bulk at 1400-1460 °C in Ar:O mixed gas.

Crystal Growing in sealed crucibles

Fig. 4 Arrangement for growing crystals in sealed crucibles to prevent CuO conversion to Cu2O and reduce evaporation.