Zr 3d Research Articles

The detailed orbital-decomposed electronic structures of tetragonal ZrO2

The detailed orbital-decomposed electronic structures of the tetragonal zirconia have been investigated by using the first-principles projector augmented wave (PAW) potential within the generalized gradient approximation (GGA) as well as taking into account the on-site Coulomb repulsive interaction (GGA+U). The deviation of the minimization energy from dz=0 to dz=±0.032 for experimental lattice constants (a=3.605Å and c=5.180Å) confirms the alternating displacement of the oxygen atoms, which causes half of the ZrO bonds stronger and the other half weaker compared with the bonds in symmetric (dz=0) zirconia. The distorted tetragonal environment of the eight oxygen anions around Zr site splits the five-fold degenerate d states of a free Zr atom into triply degenerate t2g (dxy, dyz and dzx) states and doubly degenerate eg (dz2 and dx2-y2) states. The additional covalent character upon Zr-O ionic bonds are resulted from the hybridization between the O(2s), O(2p) and Zr(5s), triply degenerate t2g (dxy, dyz and dzx) states of Zr(4d). The O(2s) and O(2p) states are clearly separated and no hybrid bonding states are formed.

First principles calculation on structural and lattice dynamic of SnTiO3 and SnZrO3

The geometry optimization, density of state (DOS) and lattice dynamic (born effective charges (BEC) and phonon dispersion) of SnTiO3 (STO) and SnZrO3 (SZO) cubic are investigated via first-principles computational methods. The results of DOS show that effect of different B-site cation–(Ti 3d, Zr 4d) states play an important role in chemical interaction particularly in changing of covalency between O2p and cation Sn-5p in STO and SZO, respectively. The BEC calculation shows the anomalous contribution to the Sn charge for both compound STO and SZO beyond the nominal charge of +2. Moreover, the replacement of Ti in STO by Zr strongly modifies the B–O interaction, suppressing the involvement change in nature of the unstable modes of SnZrO3. The results were compared and showed in good agreement with other calculated values using different methods.

First-principles APW + LO calculations and X-ray spectroscopy studies of the electronic structure of Zr6FeAl2

Electronic structure of zirconium iron aluminide, Zr6FeAl2, a very prospective hydrogen-storage intermetallic compound, has been studied from both theoretical and experimental viewpoints. In the present paper first-principles band-structure augmented plane wave + local orbitals (APW + LO) calculations as incorporated in the WIEN2k code as well as X-ray photoelectron spectroscopy (XPS) and X-ray emission spectroscopy (XES) measurements have been made to elucidate total and partial densities of states of Zr6FeAl2. Due to data of the present APW + LO calculations, the Al 3s-like states dominate at the bottom of the valence band, the central portion of the valence band is dominated by the Fe 3d-like states, whilst the top of the valence band is composed mainly by contributions of the Zr 4d-, Fe 3d- and Al 3p-like states. Furthermore, the bottom of the conduction band of Zr6FeAl2 is dominated by contributions of the Zr 4d*- and Fe 3d*-like states. Regarding the occupation of the valence band of Zr6FeAl2, the APW + LO results have been confirmed experimentally by a comparison on a common energy scale of the XPS valence-band spectrum and the XES bands representing the energy distributions of the valence Zr d-, Fe d-, Al p- and Al s,d-like states in the compound under consideration. Additionally, the XPS Zr 3d, Fe 2p and Al 2p core-level binding energies have been measured for Zr6FeAl2.

First-principles FP-LAPW calculations and X-ray spectroscopy studies of the electronic structure of Zr3V3O and Zr3V3O0.6 oxides

Electronic properties of Zr3V3O oxide, a very promising hydrogen-storage material, were studied both from theoretical and experimental points of view employing the full potential linearized augmented plane wave (FP-LAPW) method as well as X-ray photoelectron spectroscopy (XPS) and X-ray emission spectroscopy (XES). Total and partial densities of states of the constituting atoms of Zr3V3O have been derived from the FP-LAPW calculations. These data indicate that, the O 2p-like states are the dominant contributors in the bottom of the valence band, whilst the top of the valence band and the bottom of the conduction band of Zr3V3O are dominated by contributions of the V2 3d-like states, with slightly smaller contributions of the V1 3d-like states as well. Significant contributions of the Zr 4d-like states throughout the whole valence-band region and near the bottom of the conduction band are also characteristic of the electronic structure of Zr3V3O. The XPS valence-band spectra and the XES Zr Lβ2,15, V Lα and O Kα bands have been derived and compared on a common energy scale for Zr3V3O and Zr3V3O0.6 oxides. This comparison of the experimental spectra was found to be in excellent agreement with the results of the FP-LAPW calculations. In addition, the XPS Zr 3d, V 2p and O 1s core-level binding energies have been measured for Zr3V3O and Zr3V3O0.6 oxides.

Electronic structures and effective masses of photogenerated carriers of CaZrTi2O7 photocatalyst: First-principles calculations

The band structures, density of states and effective masses of photogenerated carriers for CaZrTi2O7 photocatalyst were performed using first principles method with the virtual crystal approximation. The results indicated that CaZrTi2O7 has an indirect band gap of about 3.25eV. The upper valence bands of CaZrTi2O7 are formed by O 2p states mixed with Ti 3d states, Zr 4d, 4p and 5s states, while the conduction bands are dominated by Ti 3d states, Zr 4d states and O 2p states. The calculated valence bands maximum (VBM) potential is located at 2.60V (vs. normal hydrogen electrode (NHE)), while the conduction bands minimum (CBM) potential at −0.65V. Therefore, CaZrTi2O7 has the ability to split water to hydrogen and oxygen under UV light irradiation. The calculated minimum effective mass of electron in CBM is about 1.35m0, and the minimum effective mass of hole in VBM is about 1.23m0. The lighter effective masses facilitate the migration of photogenerated carriers and improve photocatalytic performance.

Changes in the morphology and the composition of the Ag|YSZ and Ag|LSM interfaces caused by polarization

The behavior of silver as the SOFC cathode material at 600°C was investigated. Ag|YSZ|Pt, Ag|LSM|Pt and Ag|LSM|GDC|Pt systems were polarized for 24 hours applying bias of up to 0.5V. Changes in the morphology and the composition of the electrolyte surface on the cathodic side were examined by the Scanning Electron Microscopy, Energy Dispersive X Ray Spectroscopy, Atomic Force Microscopy and X-ray Photoelectron Spectroscopy. Silver dendrites arose around the contact in the Ag|YSZ|Pt and Ag|LSM|GDC|Pt cells but not in the Ag|LSM|Pt system. No changes were observed in the composition and morphology of YSZ surface below the silver cathode except the partial reduction of Zr4+ and/or formation of oxygen vacancies leading to the negative shift in the Zr 3d binding energy. In the case of the Ag|LSM|GDC|Pt cell partial decrease of the concentrations of the surface Mn species with higher than +4 oxidation state and the surface Sr species was observed.

Influence of yttria addition on the phase transformations of zirconia from zircon ore by carbothermal reduction process

Zircon ore carbothermal reduction with yttria addition has been carried out. The influences of heating temperature and yttria addition on the phase transformations of zirconia from zircon ore by carbothermal reduction have been investigated in detail. The phase transformations of zirconia from zircon ore by carbothermal reduction were monitored by X-ray diffraction. The microstructure and micro-area chemical analysis of the products were characterized by scanning electron microscopy and energy dispersive spectrometer. The chemical states of Zr 3d, Y 3d and O 1s presented in the products of zircon carbothermal reduction with 10 wt% yttria addition were investigated by X-ray photoelectron spectroscopy. The results showed that the optimized heating temperature of zircon carbothermal reduction with no addition was 1600 °C, and the main phase of the products consists of m-ZrO2, c-ZrO2, ZrC and β-SiC. Yttria addition could be introduced into zirconia lattice and caused it to form Y2O3 stabilized zirconia. Zirconia in the products would be turned into partially stabilized zirconia with yttria addition from 1 wt% to 5 wt% while it would exist in the form of fully stabilized zirconia with over 8 wt% yttria addition.

Photocatalytic H2 evolution property of Zr-doped sodium titanate nanobelts prepared by dealloying of Ti-based metallic glassy powders

The structure and photocatalytic H2 evolution property of a novel Zr-doped titanate nanobelt material fabricated by the dealloying method was studied. Using Ti-based metallic glassy powders as Ti and Zr source, the synthesized Na2(Ti0.85Zr0.15)4O9 and H2(Ti0.85Zr0.15)4O9 nanobelts show much higher photocatalytic activity than H2Ti4O9 nanobelts under UV irradiation. According to experimental results and first-principle calculations, the effect of Zr-doping on the band structure of these semiconductors was also investigated. The results show that Zr 4d orbitals played an effective role on both the valence and the conduction bands, which contributes to the enhanced photocatalytic activity. Furthermore, the H2 evolution property is determined to be dominated by the synergetic influence of the thermodynamic driving force (band structure and H+ reduction potential) and the active reaction sites.

Raman and x-ray photoelectron spectroscopy study of ferroelectric switching in Pb(Nb,Zr,Ti)O3 thin films

The ferroelectric switching process in Pb(Nb,Zr,Ti)O3 thin films was studied by performing Ramanspectroscopy and x-ray photoelectron spectroscopy (XPS). Switching was achieved using a macroscopic polarization experiment above and below the Curie temperature. Two samples in opposite switching states were obtained and characterized in order to correlate both vibrational-bands distortions of the bulk and changes in the elemental states of the surface. We have assigned the symmetrical A1(2TO) (332 cm−1) and A1(3TO) (603 cm−1) vibrational modes to the ferroelectric phase. Their corresponding peaks-area showed symmetrical behavior when the sample was polarized in opposite directions, while the quantity of phonons associated to the ferroelectric phase was conserved. We found that binding energies in the XPS signals of the Ti 2p, Nb 3d, Zr 3d, and Pb 4f levels increased when comparing to the values found in a non-polarized sample. Moreover, a high population of oxygen vacancies diffused to the surface of the ferroelectric capacitor under the application of external electric fields. Our novel results show the correlation between vibrational and ferroelectric behaviors and highlight the possibility to perform in situ treatments to decrease thedegradation of current technological capacitors.

XANES and XPS investigations of the local structure and final-state effects in amorphous metal silicates: (ZrO2)x(TiO2)y(SiO2)1−x−y

Amorphous quaternary [(ZrO(2))(x)(TiO(2))(y)(SiO(2))(1-x-y)] and ternary [(ZrO(2))(x)(SiO(2))(1-x)] silicates were synthesized using a sol-gel method and examined via XPS and XANES. Metal silicates are important industrial materials, though structural characterization is complicated because of their amorphous nature. Hard (Ti K- and Zr K-edge) and soft (Ti L(2,3)-edge) X-ray XANES spectra suggest the Ti and Zr coordination numbers in the quaternary silicates remain constant as the metal identity or total metal content (x, y, or x + y in the chemical formula) is varied. XPS core-line spectra from the quaternary silicates show large decreases in Ti 2p(3/2), Zr 3d(5/2), Si 2p(3/2), and O 1s binding energies due to increasing final-state relaxation with greater next-nearest neighbour substitution of Si for less-electronegative Ti/Zr, which was confirmed by analysis of the O Auger parameter. These decreases in binding energy occur without any changes in the ground-state energies (e.g., oxidation state) of these atoms, as examined by Ti L(2,3)-edge, Si L(2,3)-edge, and O K-edge XANES. Because most spectroscopic investigations are concerned with ground-state properties, knowledge of the contributions from final-state effects is important to understand the spectra from materials of interest.

ZrO2 and Al2O3 Thin Films on Ge(100) Grown by ALD: An XPS Investigation

Thin films of aluminium oxide (Al2O3) and zirconium oxide (ZrO2) were prepared by Atomic Layer Deposition (ALD) on p-type (100) germanium substrates. In the present work a detailed analysis of the films by X-ray photoelectron spectroscopy (XPS) in order to investigate their chemical composition is presented. This study is dedicated to an XPS investigation of the principal core levels (Al, Zr, O) of Al2O3 and ZrO2 thin films. In particular, wide scan spectra, detailed scans for the Zr 3d, Al 2p, O 1s, and C 1s regions and related data for zirconia and alumina films are presented and discussed. The results point out the formation of Al2O3 and ZrO2 films with the presence of OH groups and carbon contamination on the surface.

Band gap tuning in nanocomposite ZrO2–SnO2 thin film achieved through sol–gel co-deposition method

Transparent SnO2, nanocomposite ZrO2–SnO2 and ZrO2 thin films were prepared by sol–gel dip-coating technique. X-ray diffraction (XRD) spectra showed a mixture of three phases: tetragonal ZrO2 and SnO2 and orthorhombic ZrSnO4. X-ray photoelectron spectroscopy (XPS) gave Zr 3d, Sn 3d and O 1s spectra of the nanocomposite ZrO2–SnO2 thin film which revealed the presence of oxygen vacancies in the nanocomposite ZrO2–SnO2 thin film. Scanning electron microscopy (SEM) observations showed that microstructure of the nanocomposite ZrO2–SnO2 thin film consists of uniform dispersion of isolated SnO2 particles in ZrO2 matrix. The band gap for the ZrO2 was estimated to be 5.51 eV and that for the nanocomposite ZrO2–SnO2 film was 4.9 eV. These films demonstrated the tailoring of band gap values which can be directly employed in tuning the band gap by simply changing the relative concentration of zirconium and tin elements. Photoluminescence (PL) spectra revealed an intense emission peak at 424 nm in the nanocomposite ZrO2–SnO2 film which indicate the presence of oxygen vacancies in ZrSnO4.

Monolayer V2O5/TiO2–ZrO2 catalysts for selective oxidation of o-xylene: preparation and characterization

A series of TiO2–ZrO2 supported V2O5 catalysts with vanadia loadings ranging from 4 to 12 wt% were synthesized by a wet impregnation technique and subjected to various thermal treatments at temperatures ranging from 773 to 1,073 K to understand the dispersion and thermal stability of the catalysts. The prepared catalysts were characterized by X-ray powder diffraction (XRD), BET surface area, oxygen uptake, and X-ray photoelectron spectroscopy (XPS) techniques. XRD results of 773 K calcined samples conferred an amorphous nature of the mixed oxide support and a highly dispersed form of vanadium oxide. Oxygen uptake measurements supported the formation of a monolayer of vanadium oxide over the thermally stable TiO2–ZrO2 support. The O 1s, Ti 2p, Zr 3d, and V 2p core level photoelectron peaks of TiO2–ZrO2 and V2O5/TiO2–ZrO2 catalysts are sensitive to the calcination temperature. No significant changes in the oxidation states of Ti4+ and Zr4+ were noted with increasing thermal treatments. Vanadium oxide stabilized as V4+ at lower temperatures, and the presence of V5+ is observed at 1,073 K. The synthesized catalysts were evaluated for selective oxidation of o-xylene under normal atmospheric pressure in the temperature range of 600–708 K. The TiO2–ZrO2 support exhibits very less conversion of o-xylene, while 12 wt% V2O5 loaded sample exhibited a good conversion and a high product selectivity towards the desired product, phthalic anhydride.

Band gap and superior refractive index tailoring properties in nanocomposite thin film achieved through sol–gel co-deposition method

Transparent nanocomposite ZrO2–SnO2 thin films with molar ratio 0.1/0.9 (ZS19), 0.3/0.7 (ZS37), 0.5/0.5 (ZS55), 0.7/0.3 (ZS73) and 0.9/0.1 (ZS91) of ZrO2/SnO2 were prepared by sol–gel dip-coating technique. X-ray diffraction (XRD) spectra showed a mixture of three phases: tetragonal ZrO2 and SnO2 and orthorhombic ZrSnO4. X-ray photoelectron spectroscopy (XPS) gives Zr 3d, Sn 3d and O1s spectra on ZS55 thin film which revealed the presence of oxygen vacancies in the nanocomposite ZrO2–SnO2 thin film. Scanning electron microscopy (SEM) observations showed that microstructure of ZS55 consists of uniformly dispersed isolated SnO2 particles in ZrO2 matrix. An average transmittance greater than 85% (in UV–visible region) is observed in the films ZS55, ZS73 and ZS91, but superior optical properties was observed in ZS55 thin film. The composite system under certain compositional mixings (ZS55) displayed a refractive index supremacy over pure zirconia films which can be directly employed in extending the range of tunability of the refractive index. Besides, these films also demonstrated tailoring of band gap values. Photoluminescence (PL) spectra revealed an intense emission peak at 424nm in ZS55 sample which indicates the presence of oxygen vacancies in ZrSnO4. All these characterizations distinctly indicate a strong interrelation between the microstructural ordering and superior optical properties of the present ZrO2–SnO2 co-deposited composites.

Characterization of plasma fluorinated zirconia for dental applications by X-ray photoelectron spectroscopy

This paper discusses fluorination of biomedical-grade yttria-stabilized zirconia (YSZ) by sulfur hexafluoride plasma treatment and characterization of near-surface chemistry products by X-ray photoelectron spectroscopy (XPS). Deconvolution of the Zr 3d and Y 3d XPS core level spectra revealed formation of both ZrF4 and YF3. In addition, seven-coordinate ZrO2F5 and/or ZrO3F4 phases were deconvolved, retaining similar atomic coordination as the parent oxide and believed to have formed by substitutional displacement of oxygen by fluorine. No additional components attributed to yttria oxyfluoride were deconvolved. Argon ion sputter depth profiling determined the overlayer to be ∼4.0nm in thickness, and angle resolved XPS showed no angle dependence on component percentages likely due to fluorination extending into the grain boundaries of the polycrystalline substrates. Importantly, the conversion layer did not induce any apparent change in zirconia crystallinity by inspection of Zr-O 3d5/2,3/2 peak positions and full-width-at-half-maximum values, important for retaining its desirable mechanical properties.

First-principles study of structural, electronic and elastic properties of single crystal CuZr

Investigations into the structural, electronic and elastic properties of intermetallic CuZr compound had been conducted by the plane-wave pseudopotential method. The calculated lattice constant was consistent well with the experimental value. The absence of band gap and finite value of the density of states (DOS) at the Fermi level reveal the metallic behavior of CuZr crystal, and Zr 4d states give rise to the electrical conductivity. The calculated elastic constants for single crystal CuZr at zero pressure obey the cubic mechanical stability condition, which indicates that the cubic CuZr crystal is mechanical stable at zero pressure. By analyzing the ratio between the bulk and shear moduli, we conclude that CuZr crystal is ductile in nature. The present theoretical investigations might give prediction to polycrystalline CuZr system.

Effect of calcination atmosphere on photoluminescence properties of nanocrystalline ZrO 2 thin films prepared by sol–gel dip coating method

Highly transparent and homogeneous nanocrystalline ZrO 2 thin films were prepared by the sol–gel dip coating method. The X-ray diffraction (XRD) pattern of ZrO 2 thin films calcined in air, O 2 or N 2 shows the formation of tetragonal phase with varying crystallite size. X-ray photoelectron spectroscopy (XPS) gives Zr 3d and O 1s spectra of thin film annealed in air, which reveal zirconium suboxide component (ZrO x , 0< x<2), Zr–O bond and surface defects. An average transmittance greater than 85% (in UV–vis region) is observed in all calcined samples. Photoluminescence (PL) reveals an intense emission peak at 379 nm and weak peaks at 294, 586 and 754 nm for ZrO 2 film calcined in air. An enhancement of PL intensity and red-shift is observed in films calcined in O 2 and N 2 atmosphere. This is due to the reconstruction of zirconium nanocrystal interfaces and vacancies, which help passivate the non-radiative defects. The oxygen deficient defect, which is due to the distorted Zr–O bond, is suggested to be responsible for photoluminescence. The defect states in the nanocrystalline zirconia thin films play an important role in the energy transfer process. The luminescence defects in the film make it suitable for gas sensors development and tunable lasers.

Bonding characters of Al-containing bulk metallic glasses studied by 27Al NMR

We report very small 27Al metallic shifts in a series of Cu–Zr–Al bulk metallic glasses. This observation and theKorringa type of spin–lattice relaxation behavior suggest that s-character wavefunctionsweakly participate in bonding and opens the possibility of enhanced covalency (pdhybridization) with increasing Al concentration, in good agreement with elastic constantsand hardness measurements. Moreover, ab initio calculations show that this bondingcharacter originates from the strong Al 3p band and Zr 4d band hybridizationsince their atomic energy levels are closer to each other while the Al 3s band islocalized far below the Fermi level. This study might provide a chemical view forunderstanding flow and fracture mechanisms of these bulk glass-forming alloys.

First-principles study on alloying stability, electronic structure, and mechanical properties of Al-based intermetallics

First-principles calculations were performed to study on alloying stability, electronic structure, and mechanical properties of Al-based intermetallic compounds (AlCu 3, AlCu 2Zr, and AlZr 3). The calculated results show that the lattice parameters obtained after full relaxation of crystalline cells are consistent with experimental data. The calculation of cohesive energies indicated that the structure stability of these Al-based intermetallics will become higher with increasing Zr element in crystal. The calculations of formation energies showed that AlCu 2Zr has the strongest alloying ability, followed by AlZr 3 and finally the AlCu 3. The further analysis find out that single-crystal elastic constants at zero-pressure satisfy the requirement of mechanical stability for cubic crystals. The calculations on the ratio of bulk modulus to shear modulus reveal that AlCu 2Zr can exhibit a good ductility, followed by AlCu 3, whereas AlZr 3 can have a poor ductility; however, for stiffness, these intermetallics show a converse order. The calculations on Poisson's ratio show that AlCu 3 is much more anisotropic than the other two intermetallics. In addition, calculations on densities of states indicate that the valence bonds of these intermetallics are attributed to the valence electrons of Cu 3d states for AlCu 3, Cu 3d, and Zr 4d states for AlCu 2Zr, and Al 3s, Zr 5s and 4d states for AlZr 3, respectively; in particular, the electronic structure of the AlZr 3 shows the strongest hybridization, leading to the worst ductility.

Electrochemical activation of molecular nitrogen at the Ir/YSZ interface

Nitrogen is often used as an inert background atmosphere in solid state studies of electrode and reaction kinetics, of solid state studies of transport phenomena, and in applications e.g. solid oxide fuel cells (SOFC), sensors and membranes. Thus, chemical and electrochemical reactions of oxides related to or with dinitrogen are not supposed and in general not considered. We demonstrate by a steady state electrochemical polarisation experiments complemented with in situ photoelectron spectroscopy (XPS) that at a temperature of 450 °C dinitrogen can be electrochemically activated at the three phase boundary between N(2), a metal microelectrode and one of the most widely used solid oxide electrolytes--yttria stabilized zirconia (YSZ)--at potentials more negative than E = -1.25 V. The process is neither related to a reduction of the electrolyte nor to an adsorption process or a purely chemical reaction but is electrochemical in nature. Only at potentials more negative than E = -2 V did new components of Zr 3d and Y 3d signals with a lower formal charge appear, thus indicating electrochemical reduction of the electrolyte matrix. Theoretical model calculations suggest the presence of anionic intermediates with delocalized electrons at the electrode/electrolyte reaction interface. The ex situ SIMS analysis confirmed that nitrogen is incorporated and migrates into the electrolyte beneath the electrode.