ELECTRONIC-STRUCTURE AND ELECTRON-PHONON INTERACTION IN ALUMINUM HYDRIDES

The superconducting transition temperature of high dose H implanted Al samples has been found by Lamoise et al. , to be higher than that of pure Al. Since experimental observations indicate the possibility of H ordering, the changes in the electronic structure and the electron-phonon interaction of pure Al upon formation of AlH and AlH//2 were studied. For this purpose, the McMillan parameter eta was determined from augmented plane wave band structure results, using the Gaspari-Gyoffy model. The metal s-p bands are rather strongly affected by the metal hydrogen interaction. For both the mono- and the dihydride, a metal-hydrogen bonding band is found at the low energy side; in addition, a hydrogen-hydrogen antibonding band appears in the dihydride, below the Fermi energy E//f. Both hydrides are metallic; their density of states at E//f is of the order of 25% higher than in the pure metal. The essential results obtained for eta can be summarized as follows: while at the Al site, for both the mono- and the dihydride, eta //A//l decreases by about 50% from its value in the pure metal, the values of eta //H are found to be large, even larger than those of eta //H in PdH; this feature which can be essentially ascribed to the magnitude of the partial s and p densities of states at the H site makes these simple metal hydrides good candidates for superconductivity.