Elements of Group III

General.—An extensive series of chemical and physical measurements of 0-rhombohedral boron has been reported (density, lattice constants, microhardness, thermal expansion, electrical resistivity, melting point). The melting point was found to be 2365 K.1 

The determination of boron in silicon may be achieved by separating the B by fusion with Na202-Na2C03, followed by conversion of the B into boric acid, which may be determined by potentiometric titration.2 

A high-resolution n.m.r. spectrometer has been developed for the determination of reliable nB chemical shifts in solids containing tetrahedr-ally co-ordinated boron.3 The data reported are summarized in Table 1. 

Cragg and Weston have written an extensive review of the mass spectra jf boron compounds of all types.4 

A report has been made of nB and 14N n.m.r. data for a wide range of B-N compounds containing four-co-ordinate boron.5 Similar data have also been given for B-N, B-C, B-O, and B-S compounds with three-co-ordinate boron.6 

---

If, on the other hand, the impurity is an electron acceptor (here, elements of group III), then the new acceptor band lies closely above the valence band (see Fig. 2.3B). The electrons from the valence band pass readily into this new band and leave holes behind. These holes are the main charge carriers in p-type semiconductors. 

All the elements discussed so far, except hydrogen, have been metals. Group III contains one element, boron, that is not a metal. The elements of Group III are ... 

---