Comments on the Probable Electronic Structure of the Group II Polonides

Based on empirical evidence, it is concluded that the polonidcs of calcium, strontium, and barium are ionic semiconductors with band gaps of 4.1 eV, 3.5 eV, and 3.3 eV, respectively. The properties of zinc polonide and calcium polonide are probably similar to those of the corresponding chalcogenides with the same zinc-blende structure. However, the crystal structure of HgPo is that of NaCl, suggesting that its band structure differs from that of semi-metallic HgTe with the zinc-blende crystal structure. Of the intermetallic compounds with the formula A11nv1 , the Group IIB (zinc, cadmium, and mercury) chalcogenides (sulfides, sclenides, and tellurides) have been extensively studied, while the corresponding Group IIA (calcium, strontium, and barium) compounds have been less thnrou~hly investigated. However, because of the experimental difficulties involved, the Group II polonides have been the subject of 011;ly one experimental study, and, to the author's knowledge, no theoretical work at -all. The ohject of this note is a discussion of the data presently available, and its use to obtain some qualitative conclusions concerning the electronic structure of the Group II polonides. It is also hoped that this work will stimulate further study of these potentially interesting intermetallic compounds. The crystal structures and lattice parameters of several Group II polonides were measured at room temperature by Vier et al1 ; this is the only expe_rimental study published to date on these materials. The compounds CaPo, SrPo, and BaPo were all found to have the NaCl crystal structure, and their 0 0 0 lattice constants a0 ~t room temperature are 6.514 A, 6~796 A, and 7.119 A, respectively. It is known that the Group IIA sulfides, selenides, and