Platinum as a Metallic Material
Examples of Applications in Single Crystal Making
By virtue of its excellent oxidation and corrosion resistance and high melting point, platinum is the ideal crucible material for the production of single crystals from a large number of oxidic compounds. Examples are lithium niobate (LiNbO3, Tm = 1,257 ), which demonstrates important ferroelectric, piezoelectric and non-linear optical properties, and the scintillator material bismuth germanate (BGO, Bi4Ge3O12, Tm = 1,050 ).
The crystals are produced from the melt by the Czochralski process or the Bridgman-Stockbarger process. In the Czochralski process the melt is maintained at constant temperature in a crucible and the crystal is gradually pulled out of the melt. In the Bridgman-Stockbarger process the melt is allowed to solidify in a predetermined direction, starting from a seed crystal in a specially formed crucible. Crucibles are made from chemically pure platinum or – particularly for oxide compositions with high melting points – the oxide dispersion hardened platinum DPH.
Crystals of compounds with higher melting points than 1,500-1,600 (e.g. lithium tantalate, Tm=1,650 , yttrium-aluminum garnet, Tm = 1,970 , sapphire, Tm = 2,040) are produced in crucibles of the higher melting platinum metal iridium.