Zirconium Dihydride Research Articles

Pressure-induced novel phases with the high-Tc superconductivity in zirconium dihydride

The unprecedented structures in hydrides could be uncovered under high pressure, which probably possess unusual properties, such as high-Tc superconductivity. Here, the structural transition of ZrH2 at 0−500 GPa are comprehensively explored by using the evolutionary algorithm in the universal structure predictor combined with first-principles calculations. Three new phases are found: Pnma-ZrH2, P-3m1-ZrH2 and R-3m-ZrH2, with dynamic stability. Moreover, the sequence of phases of ZrH2 under pressure is I4/mmm → P4/nmm → Pnma → P-3m1 → R-3m with the zero-point energy effects. Structural feature, electronic properties, bonding characters and superconductivity of all the ZrH2 are analyzed in detail. More importantly, the superconducting critical temperature Tc values for P-3m1 at 440 GPa and R-3m at 500 GPa are 17.70–20.14 K and 26.68–30.03 K, respectively, which stems from the strong electron-phonon coupling.

Synthesis and characterization of zirconium diboride precursor based on polycentric bridge bonds

Zirconium diboride (ZrB2) is one of the most important ultrahigh temperature ceramics (UHTCs). ZrB2 precursor was synthesized with bis(cyclopentadienyl)zirconium dihydride (Cp2ZrH2) and borane-dimethyl sulfide complex (BH3·S(CH3)2). The influences of molar ratio of reactants and reaction temperature on the solubility of the as-synthesized precursors were investigated. The molecular structure of the precursor, pyrolysis behavior, and the composition of the derived ceramics were investigated by X-ray photoelectron spectroscopy (XPS), Fourier Transformed Infrared Spectroscopy (FT IR), Raman Spectroscopy (RMS), 1H Nuclear Magnetic Resonance Spectroscopy (1H NMR), 11B Nuclear Magnetic Resonance Spectroscopy (11B NMR), Thermogravimetric-Mass Spectroscopy (TG-MS), X-ray Diffraction (XRD), and Scanning Electron Microscopy (SEM), respectively. The results showed that, the precursor was an oligomer based on Zr–H–B polycentric bridge bonds with molecular weight of 750 and formula as (Cp2Zr(BH4)2)3. The precursor would probably further polymerize under vacuum or at high temperature and lead to an insoluble polymer. The ceramic yield of the precursor at 1000 °C was around 66% under N2 atmosphere. After pyrolyzed at 1800 °C, the derived ceramics were composed of h-ZrB2, ZrC, and free carbon with a formula as ZrB1.38C2.18.

Synthesis and characterization of zirconium diboride ceramic precursor

In the present study, ZrB2 precursor which met the requirements of polymer infiltration-pyrolysis process, was synthesized and characterized. ZrB2 precursor was synthesized with bis(cyclopentadienyl)zirconium dihydride (Cp2ZrH2), borane-dimethyl sulfide complex (BH3·S(CH3)2), and vinyltrimethylsilane ((CH3)3Si(CHCH2), VTMS). The molecular structure of the precursor, pyrolysis behavior, and the composition of the derived ceramics were investigated. The results showed that, the as-synthesized precursor was an oligomer based on Zr–H–B polycentric bridge bonds. The precursor was stable in an inert atmosphere. The ceramic yield of the precursor at 1200°C was around 65.5% under N2 atmosphere. The derived ceramics obtained under 1200°C were composed of h-ZrB2, m-ZrO2 and t-ZrO2. When the temperature was up to 1400°C, peaks of ZrC emerged due to carbothermic reduction. m-ZrO2 and t-ZrO2 disappeared with the pyrolysis temperature above 1600°C. The derived ceramics pyrolyzed at 1800°C were composed of h-ZrB2 and ZrC, and the former was the predominant phase.

Mechanical and structural stability of zirconium dihydride

First-principles calculation reveals that the ZrHx phases (x = 1, 1.25, 1.5, 1.75, and 2) with the cubic fluorite-type (fcc, δ phase) and face-centered-tetragonal (fct: ɛ phase, c/a < 1; γ phase, c/a > 1) structures are all energetically favorable with negative heats of formation of −30 to −56 kJ/(mol H) and very small structural energy differences, while mechanical stability plays a more important role in determining the existence of various ZrHx phases. Calculation also shows that the intrinsic composition range of the δ → ɛ transition of ZrHx phases is x ≥ 1.5, and that the fundamental mechanism of this transition is mechanical unstableness of the δ phase which will spontaneously transform into ɛ phase by means of the {110}<110> shear. Moreover, electronic structures show that the co-function of van Hove singularities and degenerate bands along several directions brings about the high level of density of states at or near the Fermi level and fundamentally induces the mechanical unstableness of the δ phase.

Mechanochemical Processing of Nanocrystalline Zirconium Diboride Powder

Nanocrystalline ZrB2 powder was prepared by mechanochemical processing of a zirconium (II) dihydride–boron mixture with subsequent annealing from 800°C to 1200°C. The crystallite size and morphology of the synthesized ZrB2 powders were characterized by X‐ray diffractometry, scanning electron microscopy, and transmission electron microscopy. The effects of annealing temperature on powder particle size and morphology were assessed. At 900°C or above, pure ZrB2 powder was obtained without trace quantities of residual ZrH2. The synthesized ZrB2 powder particles were spherically shaped, with a crystallite size between 5 and 40 nm. The crystallite size increased with increase of annealing temperature.

Homologation of Propane Catalyzed by Oxide‐Supported Zirconium Dihydride and Dialkyl Complexes

Unter überkritischen Bedingungen und bei moderaten Temperaturen wird Propan in Gegenwart eines Zirconium-Dihydrid-Katalysators auf einem oxidischen Material wie Siliciumoxid in stärker verzweigte Homologe überführt. Die Reaktion ähnelt der Ziegler-Natta-Olefinpolymerisation. Olefinische Einheiten, die in einer Alkylkette erzeugt werden, werden in die andere unter Bildung einer längeren Alkylkette inseriert (siehe Schema).

Homologation of Propane Catalyzed by Oxide‐Supported Zirconium Dihydride and Dialkyl Complexes

Homologation of Propane Catalyzed by Oxide‐Supported Zirconium Dihydride and Dialkyl Complexes

Synthesis of Bis(indenyl)zirconium Dihydrides and Subsequent Rearrangement to η5,η3-4,5-Dihydroindenediyl Ligands: Evidence for Intermediates during the Hydrogenation to Tetrahydroindenyl Derivatives

Exposure of eta9,eta5-bis(indenyl)zirconium sandwich complexes to 4 atm of H2 resulted in facile oxidative addition to furnish the corresponding zirconocene dihydrides, (eta5-C9H5-1,3-R2)2ZrH2 (R = SiMe3, SiMe2Ph, CHMe2). Continued hydrogenation completed conversion to the tetrahydroindenyl derivatives, (eta5-C9H9-1,3-R2)2ZrH2. Deuterium labeling studies established that dihydrogen (dideuterium) addition to the benzo rings is intramolecular and stereospecific, occurring solely from the endo face of the ligand, proximal to the zirconium. In the absence of dihydrogen, the bis(indenyl)zirconium dihydrides rearranged to new zirconium monohydride complexes containing an unusual eta5,eta3-4,5-dihydroindenediyl ligand, arising from metal-to-benzo ring hydrogen transfer. Mechanistic studies, including a normal, primary kinetic isotope effect measured at 23 degrees C, are consistent with a pathway involving regio- and stereoselective insertion of a benzo C=C bond into a zirconium hydride. The stereochemistry of the insertion reaction, and hence the eta5,eta3-4,5-dihydroindenediyl product, is influenced by the presence of donor ligands and controlled by the preferred conformation of the indenyl rings. Exposure of the zirconium hydrides containing the eta5,eta3-4,5-dihydroindenediyl rings to 1 atm of dihydrogen afforded the tetrahydroindenyl zirconium dihydride complexes, establishing the intermediacy of this unusual coordination environment during benzo ring hydrogenation.

State of Hydrogen in Cubic Zirconium Dihydride

PMR spectra have been recorded and the proton spin–lattice relaxation time has been measured for cubic hydride δ-ZrH2. It is found that above 290 K thermally activated diffusion of hydrogen takes place. In the region 230 K, a reversible phase transition takes place, which is due to a change in the state of hydrogen in the crystal lattice of zirconium dihydride. Possible mechanisms of this transition are discussed.

DFT study of the mechanism of alkane hydrogenolysis by transition metal hydrides. 1. Interaction of silica-supported zirconium hydrides with methane

Model reactions of silica-supported zirconium hydrides (≡Si—O—)3ZrH and (≡Si—O—)2ZrH2 with methane, resulting in cleavage of a C—H bond in the methane molecule and the formation of (≡Si—O—)3ZrCH3 and (≡Si—O—)2Zr(H)CH3 as products were studied using the DFT approach with the PBE density functional. The processes proceed as bimolecular reactions without preliminary formation of agostic complexes. According to calculations, zirconium dihydrides (≡Si—O—)2ZrH2 are more reactive toward the methane C—H bonds than zirconium monohydrides (≡Si—O—)3ZrH. The calculated activation energies of the reactions with participation of zirconium dihydrides (≡Si—O—)2ZrH2 are in better agreement with the known experimental data for the Yermakov—Basset catalytic system.

Electron and positron characteristics of group IV metal dihydrides

Self-consistent calculations of the electronic structure of TiH 2, ZrH 2 and HfH 2 were performed by the linear muffin-tin orbital method in the atomic sphere approximation (LMTO-ASA). The band structure of non-stoichiometric ZrH 1.75 was calculated as well. The effect of a hydrogen vacancy on the electron characteristics of zirconium dihydride was analyzed. The positron states, lifetime and the contributions of electron states to the electron-positron annihilation (EPA) processes were calculated in low positron density approximation. The results obtained are in satisfactory agreement with the experimental and other theoretical data.

Electronic structure of zirconium dihydride

Using linearized muffin-tin orbitals, with the atomic spheres corrected for overlap, we have performed a self-consistent calculation of the electronic structure of the cubic phase of zirconium dihydride. We have calculated the electronic structure of nonstoichiometric ZrH1.75. We have studied the effects of a hydrogen vacancy on the electronic characteristics. Assuming a low positron density, we calculated the positron spectrum, the positron lifetime, and the contributions to electron-positron annihilation of various electronic states. We obtained a reasonably good agreement between our theoretical results and the experimental data.

Low temperature1H NMR study of electronic structure parameters (T 1e T) in zirconium dihydride

Measurements of the proton-spin-lattice relaxation times (T1) are reported for zirconium dihydrides: ZrH1.87, ZrH1.93 and ZrH2.00 at nominal frequency of 41 MHz, with emphasis on the low temperature (4.2–25 K) behaviour of theT1. The dominant contributions are originated from the hyperfine interactions of the protons with the conduction electrons and the paramagnetic impurities. The (T1e T)−1/2 values determined from the low temperature range (4.2–25 K) agree with those obtained in the extended range (4.2–300 K) as well as with the values reported by the other researches. The paramagnetic impurity contribution is found to be small and teperature independent.

Synthesis, characterization, and chemical reactivity of zirconium dihydride [(C5H4R)2Zr(.mu.-H)H]2 (R = SiMe3, CMe3). H/D exchange reactions of anionic species [(C5H4R)2ZrH2]-. X-ray crystal structure of [(C5H4SiMe3)2Zr(.mu.-H)H

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTSynthesis, characterization, and chemical reactivity of zirconium dihydride [(C5H4R)2Zr(.mu.-H)H]2 (R = SiMe3, CMe3). H/D exchange reactions of anionic species [(C5H4R)2ZrH2]-. X-ray crystal structure of [(C5H4SiMe3)2Zr(.mu.-H)H]2Anne Marie Larsonneur, Robert Choukroun, and Joel JaudCite this: Organometallics 1993, 12, 8, 3216–3224Publication Date (Print):August 1, 1993Publication History Published online1 May 2002Published inissue 1 August 1993https://doi.org/10.1021/om00032a050RIGHTS & PERMISSIONSArticle Views185Altmetric-Citations37LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (946 KB) Get e-AlertsSupporting Info (1)»Supporting Information Supporting Information Get e-Alerts

Anomalous proton-spin-lattice relaxation at high temperatures in zirconium dihydrides.

Measurements of the proton-spin--lattice relaxation rate ${\mathit{R}}_{1}$ are reported for zirconium dihydrides, ${\mathrm{ZrH}}_{\mathit{x}}$ (1.58\ensuremath{\le}x\ensuremath{\le}1.98), with emphasis on the behavior of ${\mathit{R}}_{1}$ at high temperatures (to 1300 K). An anomalously sharp increase in ${\mathit{R}}_{1}$ is found at all hydrogen concentrations at temperatures above \ensuremath{\sim}900 K. At the onset temperature ${\mathit{T}}_{\mathit{c}}$ for anomalous ${\mathit{R}}_{1}$ behavior, defined as that of the intermediate ${\mathit{R}}_{1}$ minimum, the hydrogen hopping rate ${\ensuremath{\nu}}_{\mathit{c}}$\ensuremath{\simeq}${10}^{9}$--${10}^{10}$ ${\mathrm{s}}^{\mathrm{\ensuremath{-}}1}$, decreasing with increasing hydrogen concentration x. The anomalous behavior depends only weakly on resonance frequency and shows no correlation with the pronounced peak in the electronic density of states at x\ensuremath{\simeq}1.80. No differences were found in the behavior of pure and impurity-doped (Cr, Mn, Fe) samples. The anomalous contribution to ${\mathit{R}}_{1}$ is described by ${\mathit{R}}_{1\mathit{x}}$=A' exp(-U/${\mathit{k}}_{\mathit{B}}$T), with U\ensuremath{\simeq}0.4--1.0 eV/atom.

91Zr nuclear magnetic resonance in tetragonal ZrH 2

We report on the first observation of the 91Zr NMR signals in tetragonal phase of ZrH 2. The Knight shift and spin-lattice relaxation time in zirconium dihydride have been measured in the temperature range 155–294 K. Their analysis is referred to the electronic structure of this material. The electron density of states N( E F) and character of the d orbital wave functions at Fermi level E F are discussed.

Nuclear-magnetic-resonance studies of hydrogen antitrapping effects by impurities (Mn,Cr,Fe) in zirconium dihydride.

We report nuclear-magnetic-resonance measurements of the proton spin-lattice relaxation time ${\mathit{T}}_{1}$ in both pure and paramagnetic impurity-containing zirconium dihydrides. Measurements of the temperature dependence of the proton spin-lattice relaxation times ${\mathit{T}}_{1}$ were made on two series of ${\mathrm{ZrH}}_{\mathit{x}}$ samples (pure and impurity doped). The results show that paramagnetic impurities (Mn,Cr,Fe) contribute an additional spin-lattice relaxation rate ${\mathit{R}}_{1\mathit{p}}$, which is observed to increase in the sequence Fe\ensuremath{\rightarrow}Cr\ensuremath{\rightarrow}Mn and also to increase sharply with increasing hydrogen concentration at fixed impurity content in each case. The former result is consistent with the experimental results that the tendency towards localized moment formation in zirconium increases in the same sequence, whereas the latter may be accounted for by the antitrapping character of these impurities. Furthermore, the fit of ${\mathit{R}}_{1\mathit{p}}$ data for the ${\mathrm{ZrH}}_{1.97}$ sample doped with 500 ppm Mn or Cr yields an activation energy ${\mathit{E}}_{\mathit{a}}$=0.78 eV/atom, which is \ensuremath{\sim}75% of ${\mathit{E}}_{\mathit{a}}$ in the bulk.

Multiple insertion and carbon-carbon coupling of isocyanides. Reaction of bis(.eta.5-methylcyclopentadienyl)zirconium dihydride with isocyanides

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTMultiple insertion and carbon-carbon coupling of isocyanides. Reaction of bis(.eta.5-methylcyclopentadienyl)zirconium dihydride with isocyanidesJeffrey R. Bocarsly, Carlo. Floriani, Angiola. Chiesi-Villa, and Carlo. GuastiniCite this: Organometallics 1986, 5, 11, 2380–2383Publication Date (Print):November 1, 1986Publication History Published online1 May 2002Published inissue 1 November 1986https://doi.org/10.1021/om00142a036RIGHTS & PERMISSIONSArticle Views94Altmetric-Citations23LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (607 KB) Get e-AlertsSupporting Info (1)»Supporting Information Supporting Information Get e-Alerts

Self-consistent band structure calculations of titanium, zirconium and hafnium dihydrides

Abstract We performed self-consistent augmented plane wave calculations of the electronic energy band structure of cubic TiH2, ZrH2 and HfH2. Although qualitatively similar to previous studies, these calculations show large quantitative differences. We find differences in the ordering of energy levels, the Fermi level (FL) values of the density of states (DOS) and the characteristic bandwidths. The tetragonal distortion observed at stoichiometry makes detailed comparison with experiment tenuous; however, these calculations are in better agreement with the photoelectron data than are the non-self-consistent calculations. We also calculated the electron-phonon interaction η in these materials and found that, although the DOS at the FL is much larger than that in PdH, the quantity η on the hydrogen sites is much smaller and therefore these compounds are not superconductors.

Selective hydrogenation of benzene to cyclohexene with zirconium hydride catalysts

Hydrides of the early transition metals have been investigated as possible catalysts for the hydrogenation of aromatics. Bis(η-cyclopentadienyl)-zirconium dihydride, [(η-C5H5)2ZrH2]n catalyzes the hydrogenation of naphthalene (80–90 °C, 860 kPa H2) to tetralin and dihydronaphthalene. The solid state binary hydrides of the Group IVA, VA elements and (to a lesser extent) lanthanum and uranium hydrides, after suitable activation, catalyze the hydrogenation of benzene, a property previously associated only with Group VI to VIII metal catalysts. Under the conditions employed (liquid phase reactor, 80–180 °C, ~900 kPa H2) the relative activity of the hydrides as catalysts is as follows: ZrH2 ~ HfH2 > TiH2 > NbH ⪢ LaH3 ~ UH3 Cyclohexane is the major reaction product; with ZrH2 and HfH2, however, some cyclohexene is formed at low conversions of benzene.Solid, reduced zirconium materials isolated from reaction of excess n-butyllithium with ZrCl4 or HfCl4 in hydrocarbons catalyze the hydrogenation of benzene at 100 °C and 860 kPa H2 to yield mostly cyclohexane. However, treatment of these materials with hydrogen (and with hydrogen together with triethylamine or diethyl ether) gives modified zirconium hydride catalysts which hydrogenate benzene with relatively high (up to ~ 90%) initial selectivities for cyclohexene.