Patent GB-1153181-A (GB)
Title: Improvements in and relating to Methods of Manufacturing Crystals
IPC: C30B25/00
Filed: 1966-02-28
Abstract: 1,153,181. Crystals of inorganic substances. PHILIPS ELECTRONIC & ASSOCIATED INDUSTRIES Ltd. 28 Feb., 1966 [3 March, 1965], No. 8673/66. Headings B1B and B1G. [Also in Divisions C1 and H5] In a method of manufacturing a crystal, solid material is deposited periodically in a vessel at a position constituting a deposition site from a fluid contained in the vessel, a supply of the material is provided in the vessel at another position constituting a supply site and the temperature difference between the two positions is varied in an alternating manner over a series of temperature alternations each comprising a period of deposition from the fluid and a period of removal to the fluid of material from the position constituting the deposition site so that more material is deposited at the position constituting the deposition site than is removed therefrom. The fluid may be the vapour cf the crystal material or its constituents; a solution of the crystal material or decomposable compounds of the crystal material or its constituents in the gaseous or vapour phase, possibly mixed with a carrier gas or dissolved in a liquid or a gas above the critical point. For each alternation there is a period in which the temperature at the supply site is higher than that at the deposition site and vice versa. There may be a flow of fluid, e.g. a carrier gas, through the vessel and its composition may be periodically varied. The vessel may be elongated, with a deposition site at the centre and a supply site at each end. The central part of the vessel may be reciprocated through an intermediate zone of maximum or minimum temperature in an oven in which there is a temperature gradient, crystal growth occurring in the central part. As an alternative a reaction vessel with its axis of rotational symmetry at right angles to the direction of a temperature gradient may be used, and this may be rotated in an oven in which a constant temperature pattern exists or in which additional periodic changes of temperature are effected. The process may be carried out in a quartz envelope 2 having uniformly wound heating wire 3 and separate heatine windings 5 and 6. Ampoule 7 with crystal material at 8 and 9 is placed with its centre 12 at the centre of the tube 2, where the temperature remains constant. Windings 5 and 6 are switched on alternately for equal periods. In examples (1) to (3) gallium phosphide is used as the source and the ampoule is filled with bromine or water vapour; (4) a crystal of iron oxide is produced from Fe 2 O 3  using HCl as. the transfer gas. In further examples a similar filled ampoule is moved to and fro in a heated quartz tube in the central part of which the temperature is reduced, crystals cf gallium phosphide and Fe 2 O 3 being produced. In other examples the reaction is effected in an oven comprising a cylindrical quartz envelope having a cylindrical heating element and the reactants are placed in a rotation-symmetrical sealed vessel, in which radical and vertical temperature gradients are produced. Crystal material is thereby transferred from a supply at the periphery to produce deposition of crystal material at the centre of the base. Using this device crystals were produced of cuprous sulphide (from cuprous sulphide and sulphur in HBr vapour; and Fe 2 O 3 (from Fe 2 O 3 source in HCl atmosphere). A liquid may also be used as the fluid e.g. aluminium ammonium alum, in the bottoms of the limbs of an H-shaped vessel filled with a saturated solution of the alum gives crystals in the horizontal part of the vessel or alternatively heating the limbs.