Abstract
An investigation has been made of the preparation of high-purity molybdenum single crystals by a combination of electron-beam zone-refining and thermal anneals. The changes in impurity levels have been followed by means of resistivity ratio measurements and radiochemical analysis. The results show that the majority of the impurities are removed during zone-refining as a result of volatilisation or outgassing. Two exceptions are: tungsten, which is not reduced to any significant extent and carbon, which is progressively transported to one end of the crystal during zone-refining. Carbon can be reduced to a low level (< 4 at.ppm) subsequent to zone-refining by annealing at ~ 1600°C in an oxygen partial pressure of ~ 6 × 10 −5 Torr, and the oxygen can then be reduced to a similar level by annealing under high vacuum (< 10 −5 Torr) at ~ 1800°C. An important feature of the results is that they indicate that oxygen occupies substitutional sites when in solution in molybdenum.
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