The methods involve heating polycrystalline material above its melting point and slowly cooling it from one end of its container, where a
seed crystal is located. A single crystal of the same crystallographic orientation as the seed material is grown on the seed and is progressively formed along the length of the container. The process can be carried out in a horizontal or vertical orientation, and usually involves a rotating crucible/ampoule to stir the melt. The horizontal configuration can avoid placing stresses on the crystal due to thermal expansion and can purify the crystal at the cost of evaporation but the shape of the liquid-solid interface between the molten material and the crystal is more concave. Compared to the temperature gradient method where a temperature gradient is required along the entire length of the crucible, in vertical Bridgman method allows for a small temperature gradient only near the liquid-solid interface. The Bridgman method is a popular way of producing certain
semiconductor crystals such as
gallium arsenide, for which the
Czochralski method is more difficult. The process can reliably produce single-crystal ingots, but does not necessarily result in uniform properties through the crystal. technique and Stockbarger technique is subtle: While both methods utilize a temperature gradient and a moving crucible, the Bridgman technique utilizes the relatively uncontrolled gradient produced at the exit of the furnace; the Stockbarger technique introduces a baffle, or shelf, separating two coupled furnaces with temperatures above and below the freezing point. Stockbarger's modification of the Bridgman technique allows for better control over the temperature gradient at the melt/crystal interface. When seed crystals are not employed as described above, polycrystalline ingots can be produced from a feedstock consisting of rods, chunks, or any irregularly shaped pieces once they are melted and allowed to re-solidify. The resultant
microstructure of the ingots so obtained are characteristic of directionally solidified metals and alloys with their aligned grains.
Bagdasarov method A variant of the technique known as the
horizontal directional solidification method (
HDSM) developed by Khachik Bagdasarov () starting in the 1960s in the Soviet Union. It uses a flat-bottomed crucible made out of
molybdenum with short sidewalls rather than an enclosed
ampoule, and has been used to grow various large oxide crystals including
Yb:YAG (a laser host crystal), and
sapphire crystals 45 cm wide and over 1 meter long. However, the quality of the crystals grown by HDSM differ from the
Czochralski method, due to the problem of the problematic presence of bubbles. ==See also==