Zirconium Atoms Research Articles

Crystal Structure and Electronic Properties of New Compound Zr6.5Pt6Se19.

A new ternary nonstoichiometric Zr6.5Pt6Se19 has been discovered as a part of effort to dope Zr into the layered transitional metal chalcogenide PtSe2. With a new structure type (oC68), it is the first Pt-based ternary chalcogenide with group 4 elements (Ti, Zr, and Hf). The crystal structure adopts the orthorhombic space group Cmmm with lattice parameters of a = 15.637(6) Å, b = 26.541(10) Å, c = 3.6581(12) Å, and V = 1518.2(9) Å3. This unusual structure consists of several building units: chains of edge-sharing selenium trigonal prisms and octahedra centered by zirconium atoms, chains of corner-shared square pyramid, and square planar centered by Pt atoms. The condensation of these building blocks forms a unique structure with bilayered Zr5.54Pt6Se19 slabs stacking along the b direction and large channels parallel to the c direction within the bilayered slabs. Band structure calculations suggest that partial occupancy of Zr atoms creates a pseudo gap at the Fermi level and is likely the main cause for the stability of this new phase.

Influence of Water in the Synthesis of the Zirconium-Based Metal-Organic Framework UiO-66: Isolation and Reactivity of [ZrCl(OH)2(DMF)2]Cl.

We recently discovered that aging a solution of zirconium(IV) tetrachloride (ZrCl4) in N,N-dimethylformamide (DMF) in the presence of water, followed by the addition of a terephthalic acid linker, reduces the crystallite size of the metal-organic framework UiO-66 (Chem. Commun. 2016, 52, 6411-6414). In an effort to shed light on the nature of the aging effect and on its relationship with the crystallite size of UiO-66, we report here the isolation and structural characterization of a microcrystalline zirconium-based compound of the formula [ZrCl(OH)2(DMF)2]Cl, which is formed during the aging process. The Zr(IV) ions are coordinated by hydroxide, DMF, and chloride to produce a one-dimensional polymer. Thanks to the presence of two -OH groups per zirconium atom, [ZrCl(OH)2(DMF)2]Cl is a suitable precursor for the synthesis of UiO-66 in dry DMF, affording a product having a smaller crystallite size than that obtained from a reaction mixture having the same chemical composition but using ZrCl4 as the Zr(IV) source. By starting from ZrCl4 and generating [ZrCl(OH)2(DMF)2]Cl in situ in solution through aging, we obtained smaller crystallites as the aging time increased, proving that [ZrCl(OH)2(DMF)2]Cl plays a role in the aging process. The possible role of [ZrCl(OH)2(DMF)2]Cl in the crystallization mechanism of UiO-66 is also discussed, with emphasis on its relationship with the amount of water in the reaction mixture.

Copper-doped induced ferromagnetic half-metal zirconium diselenide single crystals

Two-dimensional (2D) magnetic layered materials have attracted considerable attention in memory storage devices due to their exciting magnetic ordering. Herein, the electronic and magnetic properties of high-quality single crystals zirconium diselenide and copper (Cu)-doped zirconium diselenide as grown via chemical vapor transport technique combined with first principle density functional theory calculations were investigated. A semimetallic state is recognized for Cu0.052Zr0.93Se2 as measured through resistance versus temperature measurements and angle resolved photoemission spectroscopy (ARPES). The magnetic measurement shows diamagnetic semiconducting behaviour for ZrSe2, whereas Cu0.052Zr0.93Se2 exhibits ferromagnetic character via applying perpendicular magnetic field. Cu0.052Zr0.93Se2 reveals the room temperature magnetic moment ∼0.0125 emu g−1, while the Curie temperature is ∼363.49 K. Furthermore, first principle density functional theory (DFT) calculations show energetically long range ferromagnetic ordering in a half-metallic Cu-doped ZrSe2, while a diamagnetic state in case of ZrSe2 agrees well with experiment results. These results suggest that due to strong interaction elements at the octahedral site of zirconium atoms when replaced by copper atoms, which can change the spin ordering of electrons and make zirconium vacancy, while their magnetic moment is increased. Very importantly the half-metallic character of Cu0.052Zr0.93Se2 promotes much spin polarized electrons around the Fermi level, suggesting significant potential in future memory devices and spintronic applications.

The effects of Cu, Zn and Zr on the solution temperature and quenching sensitivity of Al–Zn–Mg–Cu alloys

This study is aimed at exploring the effects of the addition of different amounts of Cu, Zn and Zr on the solution temperature and quenching sensitivity of Al–Zn–Mg–Cu alloys. The main concerns are that low solution temperature and high quenching sensitivity will bring about disturbances during the manufacture of AA7075 aluminum alloys. Therefore, overcoming these difficulties is the goal.It was observed in the experiments that when a high copper alloy was subjected to heat treatment over 530 °C, there was an obvious melting phenomenon at the grain boundaries. After reducing some of the copper, an homogenizing heat treatment led the eutectic T phase (Mg3Zn3Al2) and η phase (MgZn2) of the Al–Zn–Mg–Cu alloy to dissolve fully into the aluminum matrix rather than precipitating the low melting point's (~495 °C) S phase (Al2CuMg). This enhanced the alloy solution temperature and improved the solution treatment efficiency. Besides, by adding a certain amount of zinc to the alloy, the precipitation amount of strengthening phase η′(MgZn2) was increased. This compensated for the reduction in the mechanical strength of the alloy containing less copper. The results showed that the addition of the zinc atoms not only elevated the strength of the alloy, but also caused no damage to the ductility. Furthermore, the addition of zirconium atoms improved the quenching sensitivity of the alloy.

Intermetallic Cu5Zr Clusters Anchored on Hierarchical Nanoporous Copper as Efficient Catalysts for Hydrogen Evolution Reaction.

Designing highly active and robust platinum-free electrocatalysts for hydrogen evolution reaction is vital for large-scale and efficient production of hydrogen through electrochemical water splitting. Here, we report nonprecious intermetallic Cu5Zr clusters that are in situ anchored on hierarchical nanoporous copper (NP Cu/Cu5Zr) for efficient hydrogen evolution in alkaline medium. By virtue of hydroxygenated zirconium atoms activating their nearby Cu-Cu bridge sites with appropriate hydrogen-binding energy, the Cu5Zr clusters have a high electrocatalytic activity toward the hydrogen evolution reaction. Associated with unique architecture featured with steady and bicontinuous nanoporous copper skeleton that facilitates electron transfer and electrolyte accessibility, the self-supported monolithic NP Cu/Cu5Zr electrodes boost violent hydrogen gas release, realizing ultrahigh current density of 500 mA cm−2 at a low potential of -280 mV versus reversible hydrogen electrode, with exceptional stability in 1 M KOH solution. The electrochemical properties outperform those of state-of-the-art nonprecious metal electrocatalysts and make them promising candidates as electrodes in water splitting devices.

In Ukrainian

The spatial and electronic structures of cluster (Ti13ZrH22O39, Ti13ZrN2H22O37, Ti13ZrN2H22O36 ) which model pure titanium dioxide (anatase modification) and that with zirconium impurities as well as pure zirconium composition (ZrO2 content), are considered. The theoretically calculated infrared, electron and X-ray spectra of these clusters are analyzed. The spectra of small particles of zirconium are shown to be highly characteristic of the spectral transition energies and uniquely correspond to their spatial structures. It is shown that in the photoelectron spectra the energy level of Zr 3p is characteristic and its intensity in the RF spectra and position on the energy scale is slightly dependent on the chemical environment of the zirconium atom. The calculated oscillation frequency in the IR spectra of the considered clusters was determined to be “breathing” vibrations of Zr – O bonds (538 cm– 1) and stretching vibrations of Zr = O bonds (955 cm– 1). It is determined that the search for an approximate solution by imposing symmetry on a real object is appropriate, because the symmetry of the cluster corresponds to the real symmetry of the crystal. The results of the studies are compared with the properties of molecular models for the bulk and surface phases of titanium dioxide, calculated by the method of electron density functional theory (DFT). It is found that the results of spectral studies of the properties of samples of titanium dioxide can clearly indicate the presence of zirconium impurities in them, or their absence.

Reactions of titanium, zirconium and hafnium atoms with hydrogen selenide: A matrix-isolation study

Laser-ablated group IV transition metal atoms have been co-deposited with hydrogen selenide at 5 K in excess of argon. The metal atoms were observed to insert into the SeH bond of hydrogen selenide to form the novel molecules HMSeH, H2MSe, H2M(SeH)2 and HMSe (M = Ti, Zr, Hf). These species were identified by argon matrix-isolation IR spectroscopy, and their assignment is supported by 1H/2D substitution as well as quantum-chemical calculations. In Particular, the molecules H2MSe and HMSe are of interest as they are rare examples of multiple bonding between a heavier main group element and a group IV transition metal.

High pressure atomic structure of Zr–Cu metallic glass via EXAFS spectroscopy and molecular dynamics simulations

ABSTRACTIn this work, we use extended X-ray absorption fine structure (EXAFS) data collected using nano-polycrystalline diamond anvil cell to study the atomic arrangement in Zr–Cu metallic glass in high pressure (HP) conditions. To reveal the microscopic details of stress accommodation mechanism, we performed molecular dynamics (MD) simulations of the HP atomic arrangement. By comparing the experimental and the calculated Zr and Cu K-edge EXAFS signal we prove the realistic character of the computer simulations. A detailed geometrical analysis of the simulated atomic configurations shows that with increasing hydrostatic pressure the local structure of Zr–Cu amorphous alloy becomes gradually dominated by Cu-centred icosahedral structural motifs involving fivefold symmetry incompatible with crystalline ordering. The variation of the short-range order is attributed to preferential straining of mechanically soft bonds between zirconium atoms.

The recovery of phosphorus from source-separated urine by repeatedly usable magnetic Fe3O4@ZrO2 nanoparticles under acidic conditions

The separation of urine at source for phosphorus (P) recovery is attractive taking into account the high P concentration and small volume. However, the treatment of urine is still challenging due to its unpleasant odor and hygiene problems. Because the above problems could be solved by acidification to keep the pH of urine below 4, we propose a novel strategy to recover P from acidified urine using tailored hydrous zirconia-coated magnetite nanoparticles (Fe3O4@ZrO2). This strategy involves the selective adsorption of phosphate by easily separable and reusable Fe3O4@ZrO2, the desorption of adsorbed phosphate, and the precipitation of desorbed phosphate as calcium phosphate fertilizer. The results indicated that at pH 4, the P in synthetic urine was selectively adsorbed and could be exhausted using Fe3O4@ZrO2. Nearly all (>97.5%) of the sequestered P on the Fe3O4@ZrO2 nanoparticles was stripped using ≥1 M NaOH solution and ~100% of the stripped P was then successfully transformed into calcium phosphate, upon adding CaCl2 at pH >12 and a Ca/P molar ratio of 3. The liquid/solid (Fe3O4@ZrO2 particles) mixture could be conveniently separated for reuse using an external magnetic field. The reusability of the Fe3O4@ZrO2 nanoparticles in the extraction of P from synthetic urine was confirmed using five cycles of the adsorption-desorption process and their performance validated using real urine samples. The mechanism of phosphate adsorption was investigated using XPS, FTIR and zeta potential measurements, showing that phosphate was chemically adsorbed on the surface through direct coordination to zirconium atom via ligand exchange.

(μ-Di-tert-butyl-silanediolato)bis-[bis-(η5-cyclo-penta-dien-yl)methyl-zirconium

The reaction of t-Bu2Si(OH)2 with two equivalents of Cp2Zr(CH3)2 produces the title t-Bu2SiO2-siloxide bridged dimer, [Zr2(CH3)2(C5H5)4(C8H18O2Si)] or [Cp2Zr(CH3)]2[μ-t-Bu2SiO2] (1), where one methyl group is retained per zirconium atom. The same product is obtained at room temperature even when equimolar ratios of the silanediol and Cp2Zr(CH3)2 are used. Attempts to thermally eliminate methane and produce a bridging methyl-ene complex resulted in decomposition. The crystal structure of 1 displays typical Zr-CH3 and Zr-O distances but the Si-O distance [1.628 (2) Å] and O-Si-O angle [110.86 (15)°] are among the largest observed in this family of compounds suggesting steric crowding between the t-Bu substituents of the silicon atom and the cyclo-penta-dienyl groups. The silicon atom lies on a crystallographic twofold axis and both Cp rings are disordered over two orientations of equal occupancy.

Dense and pure high-entropy metal diboride ceramics sintered from self-synthesized powders via boro/carbothermal reduction approach

Equimolar quinary diboride powders, with nominal composition of (Ti0.2Hf0.2Zr0.2Nb0.2Ta0.2)B2, were synthesized by boro/carbothermal reduction (BCTR) of oxide mixtures (MO x , M = Ti, Hf, Zr, Nb and Ta) using B4C as source of B and C in vacuum. By adjusting the B4C/MO x ratios, diboride mixtures without detectable MO x were obtained at 1600°C, while high-entropy diboride (HEB) powders with particle size of 1 μm was obtained at 1800°C. The phase, morphology and solid solution evolution process of the HEB powders during the BCTR process were comprehensively investigated. Although X-ray diffraction pattern indicated the powders synthesized at 1800°C were in a single-phase AlB2 structure, elemental mappings showed that (Ta, Ti)-rich and (Zr, Nb)-rich solid solution coexisted in the HEB powders. The distribution of niobium and zirconium atoms in HEB was unable to reach uniform until the HEB powders were spark plasma sintered at 2000°C. (Ti0.2Hf0.2Zr0.2Nb0.2Ta0.2)B2 ceramics with a relative density of 97.9% were obtained after spark plasma sintering the HEB powders at 2050°C under 50 MPa. Rapid grain growth was found in this composition when the sintering temperature was increased from 2000 to 2050°C, and the averaged grain size increased from 6.67 to 41.2 μm. HEB ceramics sintered at 2000°C had a Vickers hardness of 22.44 ± 0.56 GPa (under a load of 1 kg), a Young’s modulus of ~500 GPa and a fracture toughness of 2.83 ± 0.15 MPa m1/2. This is the first report for obtaining high density HEB ceramics without residual oxide phase, benefiting from the high quality HEB powders obtained.

Deuterium ions in vacuum arc plasma with composite gas-saturated zirconium cathode in a magnetic field

Plasma containing deuterium ions has found wide application, for example and notably for generating neutron fluxes in nuclear fusion reactions. These reactions take place when a compressed plasma is heated to high temperature, or in nuclear reactions between energetic deuterium ion beams, obtained from deuterium-containing plasma, and a solid target containing heavy hydrogen isotopes. The vacuum arc discharge with composite cathode made of a metal saturated with deuterium provides one possible means for generating deuterium plasma. In the work described here, we have explored the mass-to-charge composition of the pulsed vacuum arc plasma formed from a zirconium cathode saturated with deuterium. The plasma composition is compared for cases when the cathode is deuterium-saturated and non-saturated, as well as for the case when an axial magnetic field of 0.5 T is applied in the arc cathode region. We show that the number of deuterium ions per zirconium ion in the vacuum arc plasma formed from a deuterium-saturated zirconium cathode is, on average, 1.4 which is two times greater than the number of deuterium atoms per zirconium atom in the cathode material. With a 0.5 Т magnetic field applied, this ratio increases up to 4.4. The results are discussed.

Synthesis, characterization, and ceramization of a carbon-rich SiCw-ZrC-ZrB2 preceramic polymer precursor

Abstract A precursor (PBSZ) for SiCw-ZrC-ZrB2 hybrid powder was synthesized by chemical reaction of phenol, paraformaldehyde, zirconium oxychloride, boric acid and tetraethylorthosilicate. Results show that zirconium, silicon and boron atoms have been successfully introduced into the branched structure. Decomposition of PBSZ is completed at 800 °C, and it gives amorphous carbon, SiO2, B2O3 and ZrO2 with a yield of 38% at 1200 °C. During the pyrolysis process, ZrB2 and SiC form at about 1500 °C, followed by the appearance of ZrC when the amount of B2O3 is limited. Highly crystallized ZrB2–ZrC–C powder with ZrB2 and ZrC grains evenly distributed in the carbon matrix together with randomly distributed SiC whiskers are obtained after heat-treated at 1800 °C. Further heated at 1900 °C, ZrB2 and ZrC grains grow from 200 to 500 nm, while SiC whiskers show a much smaller diameter size and tend to grow on the ZrB2–ZrC–C block surface. The morphology difference is caused by the larger gas supersaturation and accommodation coefficient of the pore channels on the block surface. In addition, defects of the carbon matrix are cumulated to the highest at 1500 °C and the structure-ordered carbon is obtained after heat treated at 1900 °C.

Oxygen-diffusion-driven oxidation behavior and tracking areas visualized by X-ray spectro-ptychography with unsupervised learning

Oxygen storage and release with oxygen diffusion in the bulk of the cerium–zirconium solid solution oxide Ce2Zr2Ox (x = 7–8), which possesses an atomically ordered arrangement of cerium and zirconium atoms, is the key to three-way exhaust catalysis. Oxygen storage proceeds via heterogeneous oxygen diffusion into the vacant sites of Ce2Zr2O7 particles, but the heterogeneous oxygen diffusion track is erased after oxygen storage in the Ce2Zr2Ox bulk. Here we show three-dimensional hard X-ray spectro-ptychography to clearly visualize the three-dimensional cerium valence map in Ce2Zr2Ox particles, and unsupervised learning reveals the concealed oxygen-diffusion-driven three-dimensional nanoscale cerium oxidation behavior and tracking areas inside individual mixed-oxide particles during the oxygen storage process. The described approach may permit the nanoscale chemical imaging of reaction tracking areas in solid materials.

First-principles calculation of mechanical properties of simulated debris Zr x U1− x O2

ABSTRACT To elucidate the mechanical properties of fuel debris inside the Fukushima Daiichi Nuclear Power Plant, we use first-principles calculations to evaluate mechanical properties of cubic Zr x U1− x O2, which is a main component of the fuel debris. We focus on the dependence of mechanical properties on the fraction x of zirconium and compare our results with recent experiment of simulated debris, in which dependences of elastic moduli and fracture toughness on the ZrO2 content showed deviation from a simple linear relation. We show that elastic moduli drop at around x = 0.25 and increase again for larger values of x, as has been observed in experiments. The reason of the drop is a softening owing to disordered atomistic structures induced by the solute zirconium atoms. We also find that stress–strain curves for the x = 0.125 case show marked hysteresis owing to the existence of many meta-stable states. We show that this hysteresis leads to slightly increased fracture toughness, but it is not enough to account for the significant increase of fracture toughness observed in experiments.

First-Principles Study of the Influence of Zirconium on the Diffusion of Uranium Defects in Uranium Dioxide

The migration properties of uranium vacancies and interstitials in zirconium-doped uranium dioxide are studied by using density functional theory (DFT) and the climbing-image nudge elastic band (CI-NEB) method. The strong correlations among uranium 5f electrons were described by using a spherically averaged Hubbard parameter. In the model, the zirconium atoms are introduced by replacing the uranium atoms at the nearest and the next nearest neighbor sites along the diffusion path of uranium defects. The doping with zirconium obviously reduces the migration barriers for defects in uranium dioxide. The effect of doping with zirconium on the diffusion of uranium defects decreases with increasing distance between the zirconium dopant and the uranium defects. Further, we investigated the lattice distortion and the electron transfer associated with the migration of uranium defects, and we analyzed the physical origin of the reduction in the migration barriers caused by zirconium doping.

Structural Characterization and Electrochemical Performance of Zr1−xTixCr0.7Mo0.3Ni Alloys

Three specimens were synthesized presenting the following stoichiometry: Zr1−xTixCr0.7Mo0.3Ni (x = 0.3; 0.5; 0.7). The substitution of zirconium atoms by a lower atomic radius metal, such as titanium, leads to the formation or inhibition of Laves and body-centered cubic phases. They are conformed as zirconium or titanium Laves phase multicomponent alloys. Titanium inclusion induces a volume contraction of the C14 Laves phases. Moreover, the abundance of the metallic titanium hexagonal phase is reduced, while the presence of crystalline phases with spatial group Im-3m is increased. Correlation between structural properties and electrochemical performances is studied before and after thermal treatments. It is concluded that segregation of metallic titanium, with a hexagonal crystalline system has a negative effect on thermodynamic and kinetic behaviors. However, body-centered cubic crystalline phases exhibit favorable outcomes for the storage capacity and time diffusion constant. TiNi phases have positive results on activation and reversibility. Laves phases are those that exhibit the larger capacity storage performance.

Differences in local structures around zirconium atoms in Eu2Zr2O7 and La2Zr2O7

Extended X-ray absorption fine structure (EXAFS) analyses of the Eu2Zr2O7 and La2Zr2O7 pyrochlore composition oxides were performed to examine differences in the local structures around the Zr atoms. In the EXAFS analyses of Eu2Zr2O7, the amplitude reduction factor of Zr16c-O8a was considerably large, indicating that a part of the oxygen vacancy site (8a) was occupied by oxide ions. Furthermore, the occupancy of the 8a site determined by Rietveld refinement of the X-ray diffraction data for Eu2Zr2O7 was 0.32(2), which was consistent with the EXAFS results. From the EXAFS analyses of La2Zr2O7, oscillation in the high wavenumber k-range sharpened with decreasing temperature, and the mean square relative displacement (MSRD) values of the ZrO peak in the R-space were small compared to those of Eu2Zr2O7. Therefore, the disorder in the local structures around the Zr atoms of La2Zr2O7 was determined to be smaller than that of Eu2Zr2O7.

Molecular dynamics of liquid Zirconia: effect of pressure

This paper carefully examined the influence of pressure within the range of (0 – 20) GPa on the selfdiffusion coefficients of zirconium and oxygen in cubic zirconia by a molecular dynamics (MD) simulations at a temperature of 3000 K using 96 -1500 particles. Data obtained showed that, at 96 particles the self-diffusion coefficients decreased from 1.60 x 10 -4 (A2/ps) to 0.76 x 10 -4 (A2/ps) between 0.0 GPa and 20.0 GPa. As the pressure is increased, the self-diffusion coefficient for zirconium and oxygen atoms decreases. Particularly, in the region of high pressure, the decrease in selfdiffusion coefficient for oxygen is nonlinear. This might be as a result of instability associated with large systems where one oxygen atom moves over the maximum potential of another oxygen atom. This is consistent with previous MD studies for oxygen in liquid SiO 2 . The pair correlation function was found to increase with pressure. These thermo physical properties find practical applications in the electro ceramic industry. Keywords : molecular dynamics, self-diffusion coefficient, liquid zirconia, pair correlation.

Identification of the strong Brønsted acid site in a metal-organic framework solid acid catalyst.

It remains difficult to understand the surface of solid acid catalysts at the molecular level, despite their importance for industrial catalytic applications. A sulfated zirconium-based metal-organic framework, MOF-808-SO4, was previously shown to be a strong solid Brønsted acid material. In this report, we probe the origin of its acidity through an array of spectroscopic, crystallographic and computational characterization techniques. The strongest Brønsted acid site is shown to consist of a specific arrangement of adsorbed water and sulfate moieties on the zirconium clusters. When a water molecule adsorbs to one zirconium atom, it participates in a hydrogen bond with a sulfate moiety that is chelated to a neighbouring zirconium atom; this motif, in turn, results in the presence of a strongly acidic proton. On dehydration, the material loses its acidity. The hydrated sulfated MOF exhibits a good catalytic performance for the dimerization of isobutene (2-methyl-1-propene), and achieves a 100% selectivity for C8 products with a good conversion efficiency.