title: WH(n) under pressure.
abstract: An initial observation of the formation of WH under pressure from W gaskets surrounding hydrogen in diamond anvil cells led to a theoretical study of tungsten hydride phases. At P = 1 atm no stoichiometry is found to be stable with respect to separation into the elements, but as the pressure is raised WH(n) (n = 1-6, 8) stoichiometries are metastable or stable. WH and WH(4) are calculated to be stable at P > 15 GPa, WH(2) becomes stable at P > 100 GPa and WH(6) at P > 150 GPa. In agreement with experiment, the structure computed for WH is anti-NiAs. WH(2) shares with WH a hexagonal arrangement of tungsten atoms, with hydrogen atoms occupying octahedral and tetrahedral holes. For WH(4) the W atoms are in a distorted fcc arrangement. As the number of hydrogens rises, the coordination of W by H increases correspondingly, leading to a twelve-coordinated W in WH(6). In WH(8) H(2) units also develop. All of the hydrides considered should be metallic at high pressure, though the Fermi levels of WH(4) and WH(6) lie in a deep pseudogap. Prodded by these theoretical studies, experiments were then undertaken to seek phases other than WH, exploring a variety of experimental conditions that would favor further reaction. Though a better preparation and characterization of WH resulted, no higher hydrides have as yet been found.
authors.affiliation: Laboratory of Atomic and Solid State Physics and Cornell Center for Materials Research, Cornell University, Clark Hall, Ithaca, NY 14853, USA. patryk.ze@cornell.edu
authors.forename: Patryk
authors.initials: P
authors.lastname: Zaleski-Ejgierd
authors.forename: Vanessa
authors.initials: V
authors.lastname: Labet
authors.forename: Timothy A
authors.initials: TA
authors.lastname: Strobel
authors.forename: Roald
authors.initials: R
authors.lastname: Hoffmann
authors.forename: N W
authors.initials: NW
authors.lastname: Ashcroft
mesh_terms: D006859:Hydrogen / Q000737:chemistry*; D008958:Models, Molecular; D008968:Molecular Conformation; D011312:Pressure; D013816:Thermodynamics; D014414:Tungsten / Q000737:chemistry*
chemical_list: D006859:Hydrogen; D014414:Tungsten