Contribution à l'étude des borures à teneur élevée en bore

Abstract

The structures of borides of the type X-B 4, XB~, (XNa)B e and XB~2 are described, X being an element in which the d shell immediately below the valency electrons is empty. The coordination of boron atoms by boron is 3 or 5. The boron radii are of two kinds: in the rigid covalent B-B bonds the radius varies little from 0.86 /~; in the boron-metal bonds, however, it varies between 0.86 and 1.10 /~. Paullng's theory does not give a satisfactory quantitative evaluation of the valencies in these borides; Kiessling reached a similar conclusion in his study of borides of lower boron content