Patent ID: 7670578

Claim:
A method of preparing a polycrystalline block of at least 10 g of a halide of formula A c Ln f X (3f+e) , wherein: Ln represents one or more rare earth elements; X represents one or more halogen atoms selected from the group consisting of C 1 , Br and I; A represents one or more alkali metals selected from the group consisting of K, Li, Na, Rb and Cs; e, which may be zero, is less than or equal to 3f; f is greater than or equal to 1; and the polycrystalline block comprises less than 0.1% by weight of water and less than 0.2% by weight of rare-earth oxyhalides; the method comprising: heating a mixture of at least one compound having at least one LN—X bond and NH 4 X and/or NH 4 X provided in a complex to obtain a molten mass comprising the rare-earth halide of the formula A e Ln f X (3f+e) ; and cooling the molten mass to obtain the polycrystalline block; wherein: the NH 4 X and/or the NH 4 X provided in a complex is present in the mixture in an amount sufficient to provide the rare-earth oxyhalides content of less than 0.2% by weight; heating the mixture comprises heating to a temperature that exceeds a melting point of the rare-earth halide of the formula A e Ln f X (3f+e) ; and when the mixture is heated to a temperature of 300° C., a temperature of at least 200° C. is maintained until the molten mass is obtained.