The role of π-blocking hydride ligands in a pressure-induced insulator-to-metal phase transition in SrVO2H

Abstract

Transition-metal oxyhydrides are of considerable current interest due to the unique features of the hydride anion, most notably the absence of valence p orbitals. This feature distinguishes hydrides from all other anions, and gives rise to unprecedented properties in this new class of materials. Here we show via a high-pressure study of anion-ordered strontium vanadium oxyhydride SrVO2H that H− is extraordinarily compressible, and that pressure drives a transition from a Mott insulator to a metal at ~ 50 GPa. Density functional theory suggests that the band gap in the insulating state is reduced by pressure as a result of increased dispersion in the ab-plane due to enhanced Vdπ-Opπ-Vdπ overlap. Remarkably, dispersion along c is limited by the orthogonal Vdπ-H1s-Vdπ arrangement despite the greater c-axis compressibility, suggesting that the hydride anions act as π-blockers. The wider family of oxyhydrides may therefore give access to dimensionally reduced structures with novel electronic properties.

Versatile and Highly Efficient Controls of Reversible Topotactic Metal–Insulator Transitions through Proton Intercalation

“…[11,24,37,38] Very recently, the search for new functionalities through non-metallic elemental doping (e.g., hydrogen and nitrogen) as cation or anion in perovskite oxides has become highly active [5,8,9,39,40] as a result of the different ionic radii, charge, and electronegativity among oxygen, nitrogen, and hydrogen. [8,[41][42][43][44] This rational synthesis strategy has recently provided an alternative approach to effectively tune structural and chemical varieties and the consequential functionalities of complex-oxide compounds. [6,8,39,41,[45][46][47] These methods, however, generally involve time-consuming processes (i.e., several hours) or high-temperature annealing (T > 400°C) in to achieve the desired effects.…”

LaSr3NiRuO4H4: A 4d Transition‐Metal Oxide–Hydride Containing Metal Hydride Sheets

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The synthesis of the first 4d transition metal oxidehydride,LaSr 3 NiRuO 4 H 4 ,isprepared via topochemical anion exchange.Neutron diffraction data showthat the hydride ions occupyt he equatorial anion sites in the host lattice and as aresult the Ru and Ni cations are located in aplane containing only hydride ligands,au nique structural feature with obvious parallels to the CuO 2 sheets present in the superconducting cuprates.DFT calculations confirm the presence of S = 1 = 2 Ni + and S = 0, Ru 2+ centers,b ut neutron diffraction and mSR data show no evidence for long-range magnetic order between the Ni centers down to 1.8 K. The observed weak inter-cation magnetic coupling can be attributed to poor overlap between Ni 3d z 2 and H1si nthe super-exchange pathways.

Complex transition-metal oxides continue to be the subject of extensive study because they exhibit aw ide variety of interesting physical and chemical properties.T hese range from magnetoresistance,high-temperature superconductivity, and collective magnetism, to ferroelectricity,ionic conductivity,a nd unusual catalytic and photocatalytic behavior. [4] Theresulting metallic state exhibits significant twodimensional character because the hydride ions limit dispersion of the p-symmetry bands,which span the Fermi level, along the z-axis.Despite their many attractive features,o nly ah andful of transition-metal oxide-hydride phases have been prepared to date.The few reported systems can be separated into different groups on the basis of the mechanism by which the metastable oxide-hydride phase is stabilized with respect to decomposition to the elemental transition metal and water (AMO x H y ! Themost obvious difference between oxide and hydride ions is their charge,a saresult of which hydride-for-oxide substitution necessarily involves reduction, allowing access to unusually low transition-metal oxidation states.T he conversion of insulating A II TiO 3 oxides into metallic A II TiO 3Àx H y oxide-hydrides is aclassic example of the use of hydride-foroxide substitution to modify materials properties.

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“…[4] Theresulting metallic state exhibits significant twodimensional character because the hydride ions limit dispersion of the p-symmetry bands,which span the Fermi level, along the z-axis. Themost obvious difference between oxide and hydride ions is their charge,a saresult of which hydride-for-oxide substitution necessarily involves reduction, allowing access to unusually low transition-metal oxidation states.T he conversion of insulating A II TiO 3 oxides into metallic A II TiO 3Àx H y oxide-hydrides is aclassic example of the use of hydride-foroxide substitution to modify materials properties.…”

A Partial Anion Disorder in SrVO2H Induced by Biaxial Tensile Strain

“…The resulting fully anion-ordered structure of [SrH] and [VO 2 ] layers can be regarded as a half-filled (d xz/yz ) 2 system. Hydride anions at the apical sites function as "π-blocker" ligands [9], making this oxyhydride a quasi-two-dimensional Mott insulator [10]. A partial trans-preference has been proposed for the 6H-type perovskite BaVO 3−x H x (0.5 < x < 0.9) where the d-electron count, n, is 1.5 < n < 1.9 [11].…”