1. K. Davies and D. Murphy, Rare Earth Products Ltd., U.K., private communication.
2. The preparation and properties of “ultrapure” metals;Spedding,1969
3. The effect of impurities, particularly hydrogen, on the lattice parameters of the “ABAB” rare earth metals
4. Effects of Impurities on Higher Order Phase Transitions
5. “ultrapure” metals;Cadieu,1969