Techniques for the Growth of Large Single Crystals of Potassium of High Purity.

The preparation of large, high purity, single crystals of potassium is described. First, high initial purity is obtained by careful zone refining. Then, a modification of the Bridgman technique is applied which leads to crystals with resistivity ratios up to 6800 at 4.2 °K. The modification consisted of a heat shield as described in the test. We concluded from the magnetoacoustic experiments that were subsequently done with these samples, that the samples had mean free paths of the order of 10 cm. Typical crystals were ⅞ in diam and about 8 in long, with growth direction along [110]. A description is given of an easy method of orientation as well as the use of a spark erosion technique to cut and polish the surfaces.