BAND-STRUCTURE AND CHEMICAL BONDING OF THE HYDRIDE PHASE OF THE TI3P-H SYSTEM

The stability of five different conceivable tetrahedral hydrogen sites in the beta-V3S type phase of the TI3P-H system has been studied by m eans of electronic band structure and total valence energy calculation s. The result shows that the stability of the different hydrogen posit ions is related to the differences in the bonding of the nearest metal neighbours: the most stable hydrogen sites are surrounded by those ti tanium atoms having weaker bonds to the phosphorus atoms. Comparisons with the hydrogen solid solution in Ti3P in the Ti3P structure type sh ow that the titanium atoms are less strongly involved in bonding to th e phosphorus atoms in the beta-V3S type structure. Consequently, the f ormation of bonds to hydrogen has a larger effect on the latter struct ure type and results in the experimentally observed structural change from the T1(3)P to the beta-V3S type structure at higher hydrogen cont ents.