ZrO2 Crystals Research Articles

Programmed Fabrication of Metal Oxides Nanostructures Using Dual Templates to Spatially Disperse Metal Oxide Nanocrystals

Multiwalled carbon nanotubes (MWCNTs) and metal oxide composites, including MWCNTs@SnO2, MWCNTs@ZrO2, MWCNTs@Fe2O3, as well as corresponding metal oxides (MO) hollow structure consisted of SnO2, ZrO2, or CeO2 metal oxide single crystals, respectively, are produced using porous carbonaceous coating and multiwalled carbon nanotube core as dual templates. The synthesis procedure involves programmed steps in which the templates are removed in a controlled sequence. The carbonaceous layer coated on MWCNTs provides porous surface for the adsorption of metal oxide precursors and a buffer zone to help the dispersion of metal oxide nanocrystals. The MWCNTs provide mechanical supports during the whole process before they are removed. MWCNTs@MO nanocomposite are obtained by the removal of the porous carbonaceous layer, and metal oxides hollow structure is produced after the removal of the MWCNTs. MWCNTs@SnO2 nanocomposite shows excellent lithium storage property as anode material for lithium-ion batteries, and SnO2 hollow structure shows high sensitivity and response rate as gas sensor material.

Impact of interface variations on J– V and C– V polarity asymmetry of MIM capacitors with amorphous and crystalline Zr (1−x)Al xO 2 films

Polarity asymmetries in J– V and C– V characteristics of symmetrical MIM capacitors with amorphous and crystalline Zr (1− x )Al x O 2 films and TiN electrodes are evaluated. Physical analysis of the interface between the TiN bottom electrode and the ZrO 2 layer reveals that the TiN bottom electrode undergoes enhanced oxidation during crystallization of ZrO 2. Simultaneously, nitrogen is incorporated into ZrO 2 near the TiN interface, and an intermixing of ZrO 2 and TiO 2 was identified by AR-XPS and SIMS. This asymmetry results in significant band offset differences for top and bottom electrodes of the crystalline MIM capacitor. Conduction mechanisms are correlated to amorphous vs. crystalline film properties. In addition, asymmetrical charge trapping and a higher trap density is found for crystalline Zr (1− x )Al x O 2 compared to amorphous films, leading to a polarity dependence in the leakage currents.

Up‐ and Down‐Conversion Cubic Zirconia and Hafnia Nanobelts

One-dimensional (1D) metal oxide nanomaterials, such as zinc oxide (ZnO) nanowires and nanobelts (or nanoribbons), have recently attracted immense attention due to their sizeand shape-dependent optical, mechanical, and electronic properties. In stark contrast, investigations of 1D zirconia (ZrO2) and hafnia (HfO2) nanomaterials remain unexploited largely because of the formidable challenges associated with the fabrication of these structures with controlled dimensions and crystal phases. ZrO2 and HfO2 materials typically exhibit three primary polymorphs (monoclinic, tetragonal, and cubic) and have important technological applications as catalyst supports, oxygen detectors, hightemperature fuel cell electrolytes, gate dielectric in metaloxide semiconductor devices, and optical waveguides. Apart from a few rare examples of rod-like polycrystalline structures formed via porous alumina templates or by using an inverse microemulsion technique, most of the ZrO2 nanomaterials obtained thus far are best classified as nanoparticles and thin films. Here, we introduce a direct and scalable approach, based upon a thermal decomposition method under normal atmospheric pressure, for growing well-defined single-crystalline cubic ZrO2 and HfO2 nanobelts with controllable structural compositions and novel optical properties. To the best of our knowledge, these nanomaterials provide the first evidence of ZrO2 and HfO2 crystals with belt-like morphology. In a typical synthesis of the ZrO2 precursors, a solution of ZrCl4 (1.6 g, 7 mmol) and YCl3 6H2O (0.3 g, 1 mmol) in ethanol (10mL) was first treated with sodium hydroxide (1.5 g, 38 mmol) to yield a viscous gel mixture. The mixture was transferred into a 15mL Teflon-lined autoclave and heated at 140 8C for 24 h. Upon cooling the resulting precipitate was

Magnetism without magnetic impurities in oxides ZrO2 and TiO2

We apply the density functional technique to investigate the magnetism induced in transition metal dioxides ZrO2 and TiO2 by substitution of the cation by a vacancy or an impurity from groups 1A or 2A of the periodic table, where the impurity is either K or Ca. It is demonstrated that the vacancy and the K-impurity leads to a robust induced magnetic moment on the surrounding O-atoms for both the cubic ZrO2 and rutile TiO2 host crystals. The native O-vacancy does not induce a magnetic moment in the host dioxide crystal.

Synthesis of pyroxene pyroceramics in large solar furnace with ZrO2 crystallization nucleator

Research on the development of zirconium-containing pyroxene glass-ceramic materials with high mechanical and chemical stability has been performed.

Preparation and properties of Y2O3 partially stabilized ZrO2 crystals

We have studied the effect of composition and growth conditions on the structure and properties of 2.5–5 mol % Y2O3 partially stabilized ZrO2 crystals grown by directional solidification in a cold-wall crucible. The phase composition and density of the crystals have been determined. The crystals are shown to be uniform in composition, with local changes in Y2O3 content within ±0.5 mol %. The dimensions and quality of the single crystals are influenced by the growth conditions.

Three-dimensional microphotonic crystals of ZrO2 toughened Al2O3 for terahertz wave applications

This letter reports an approach, based on microstereolithography, to create three-dimensional photonic crystals of microscale structure made of ceramic-resin composite (before sintering) and dense ceramics (after sintering). For ZrO2 toughened Al2O3 ceramic-resin photonic crystals (with a lattice constant of 500μm), the forming resolution was around 10μm and the measured band gap appeared between 350 and 400GHz in the Γ-X ⟨100⟩ direction, 350 and 400GHz in the Γ-K ⟨110⟩ direction, and 270 and 360GHz in the Γ-L ⟨111⟩ direction. After sintering, the lattice constant shrunk to 380μm and the band gap was between 320 and 420GHz in the Γ-X ⟨100⟩ direction, 330 and 400GHz in the Γ-K ⟨110⟩ direction, and 260 and 355GHz in the Γ-L ⟨111⟩ direction.

Synthesis of Tetragonal ZrO2 Nanocrystals with a High Proton Conductivity

Abstract Pure tetragonal ZrO2 nanocrystals were prepared at low temperature (85 °C). Their proton conductivity measured at 80 °C in N2 is 5.63×10−5 S/cm which is one order of magnitude higher than that of 1.72×10−6 S/cm for the sulfated counterpart or of 4.17×10−6 S/cm reported in the literature for 3-nm crystals of ZrO2·nH2O.

Structural characteristics of nanocrystalline ZrO2 powder sol–gel derived to luminescent applications

Interest in nanocrystalline ceramics is increasing nowadays. Sol–gel is a low temperature method, which uses chemical precursors to produce ceramics and glasses with better purity and homogeneity than the conventional high-temperature processes. This new preparation method of nanophosphors has been recently strongly developed for producing high-efficiency luminescent devices. When producing ZrO2 it is important to retain a high degree of crystallization of ZrO2 and its possible correlation with the concentration of defects. The X-ray diffraction patterns of ZrO2 showed that the calcined material has a strongly monoclinic structure. The thermoluminescent glow curve of ZrO2 exhibited two peaks. Photoluminescence spectra of ZrO2 also were obtained.

Microstructural characterization and crystallization of ZrO2–Y2O3–CuO solid solution powders

Abstract ZrO 2 –Y 2 O 3 –CuO powders were prepared by coprecipitation method. The effects of CuO content and calcining temperature on phase structure, grain size and lattice parameters were studied. The dopants CuO inhibited the increase of crystallite size and made the lattice parameter decrease. The results show that the solid solution forms between ZrO 2 –Y 2 O 3 and CuO. The obvious advantage of ZrO 2 –Y 2 O 3 –CuO solid solution powders is that the sintering temperature decreased to as low as 900 °C.

Sol–gel derived TiO2:ZrO2 multilayer thin films for humidity sensing application

Abstract In the present work, we describe humidity sensing properties of nano-structured multilayered TiO2:ZrO2 ceramic thin films prepared by sol–gel processing. An enhancement in the sensitivity is observed for both TiO2/ZrO2 (TZ) and ZrO2/TiO2 (ZT) thin film samples that are annealed at 400 °C, due to simultaneous crystallization of ZrO2 and TiO2. The multilayered ZrO2:TiO2 thin film shows less drift and low hysteresis compared to pure TiO2. The experimental data are fitted to an equivalent circuit containing a resistance and a non-Debye capacitance in parallel. Typical response and recovery time of the sensor are 56 and 124 s, respectively. We demonstrate the possibility of a practical device without heating the humidity sensitive element for regeneration.

Electronic structure of negative oxygen ion in ZrO2 crystal

AbstractWith a rapid downscaling of the complementary metal‐oxide‐semiconductor (CMOS) devices, the ZrO2 becomes a promising candidate for application in microelectronic and therefore the information about the electronic structure of the perfect and defect ZrO2 crystal becomes important. In the present study, the local orbital Hartree–Fock approximation was applied to the ZrO2 crystal electronic structure calculations. The noncanonical orbitals localized on ions were employed, which are the solutions of the Hartree–Fock equations for ions in the confining potential simulating the crystal environment. The confining potential was calculated selfconsistently to bring the minimum to the crystal energy. The cluster expansion for the crystal energy was employed. The general idea of the method is similar to that of the study (1978, 20, 565), devoted to the electronic structure calculations of MgO crystal. In the present study, the more complicated system is considered. First, ZrO2 crystal has lower symmetry, and second the d‐orbitals are present among ions occupied orbitals. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2007

The influence of alcohol additives on the crystallization of ZrO2 under hydrothermal conditions

ZrO2 small particles with different crystal habits were prepared from zirconium nitrate under hydrothermal conditions. The ZrO2 particles were characterized by XRD, TEM and SEM. The crystal structure, morphology and size of the ZrO2 particles were strongly dependent on the glycerin additive in the reaction solution. The phase-pure t-ZrO2 with the size about 10 nm formed from the reaction solution added with glycerin while the rod-like phase-pure m-ZrO2 with the size about 30 × 80 nm formed from the reaction solution without glycerin (180 °C, 18 h, pH = 13). The t-ZrO2 could also form under the same hydrothermal conditions in the presence of other polyhydric alcohol additives, such as trimethylolpropane and tetramethylolmethane. But monohydric and dihydric alcohols were not benefits to formation of phase-pure t-ZrO2. The mechanisms for formation of phase-pure t-ZrO2 were supposed according to the experimental results.

Fabrication of SiO2-ZrO2 composite fiber mats via electrospinning

(1 − x)SiO2-(x)ZrO2 (x = 0.1, 0.2) composite fiber mats were prepared by electrospinning their sol-gel precursors of zirconium acetate and tetraethyl orthosilicate (TEOS) without using a polymer binder. The electrospun composite fibers were characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), fourier transform infrared spectroscopy (FT-IR) and mercury porosimetry. The composite fibers having a tetragonal crystalline ZrO2 were obtained by calcining the electrospun composite fibers at high temperatures. The results show that the structure and crystallization of ZrO2 in the composite fibers can be controlled by sintering temperature, while the porosity and morphology of the fiber mats did not depend on the sintering temperature.

The upconversion luminescent of Er3+/Yb3+ co-doped ZrO2-Al2O3 powders

Samples of Er3+/Yb3+ co-doped ZrO2-Al2O3 powders were prepared by solid-state reaction. The upconversion luminescence spectrum excited by 980 nm laser light suggests that there exit three main emission bands: one red emission band centered at 654 nm and two green emission bands centered at 545 and 525nm, corresponding to Er3+ ions transitions of 4F9/2→4I15/2, 4S3/2→4I15/2 and 2H11/2→4I15/2, respectively. The emission band centered at 654 nm is much stronger than the other two. The upconversion mechanisms are discussed and it is found that both red emission and green emissions are two-photon processes. It can be seen from the XRD spectra that zirconia (ZrO2) mainly exists as a cubic phase,while Al3+ is implanted into the ZrO2 lattice, producing the ZrO1.87. The solid solution towers the site symmetry of the lattices in ZrO2 crystals, which promotes the upconversion efficiency.

Free-energy calculations for the cubic ZrO2 crystal as an example of a system with a soft mode

We calculate the free energy for a crystalline ZrO(2) with a soft mode by the first-principles method, using the double-well energy-displacement relation. The soft-mode branch is considered as an ensemble of independent anharmonic oscillators of the parabola-plus-Gaussian or of the 2-4 polynomial forms. The anharmonic contributions are included to reproduce the cubic-to-tetragonal phase transition, however, it appears that the cubic phase does not become the most stable within the framework of the independent oscillators approach.

One-pot synthesis and optical properties ofEu3+-dopednanocrystalline TiO2 and ZrO2

A simple and versatile one-pot sol–gel synthesis ofEu3+-dopednanocrystalline TiO2 and ZrO2 nanomaterials is reported in this paper. It consists of the controlled crystallization ofEu3+-dopedTiO2 orZrO2 nanoparticles from an initial solution containing the metal alkoxide, the lanthanideprecursor, a complexing agent and a non-complexing acid. The main interest is that itcould be extended to different lanthanide ions and inorganic metal oxides to prepare othermultifunctional nanomaterials.The characterization by XRD, HRTEM and SAED techniques showed that theTiO2 and ZrO2 crystallization takes place at very low temperatures(60 °C) and that the crystallite size can be tailored by modifying the synthetic conditions. The opticalproperties of the resulting materials were studied by emission spectra and decay measurements. BothEu3+:TiO2 and Eu3+:ZrO2 samples exhibited long lifetime values after removing organic components(τ = 0.7 and 1.3 ms,respectively), but the Eu3+:ZrO2 system is specially promising for photonic applications since itsτ value is longer than some reported for other inorganic or hybrid matrices in whichEu3+ ions arecomplexed. This behaviour has been explained through an effective dispersion of the lanthanide ions withinthe ZrO2 nanocrystals.

Influence of grinding and atmosphere on the crystallization of ZrO2gel

Influence of grinding and atmosphere on the crystallization of ZrO₂gel

Mechanical properties of ZrO2 ceramic stabilized by Y2O3 and CeO2

ZrO2 ceramic was made from evenly dispersed (Y, Ce)-ZrO2 powder with different compositions, which was prepared by the chemical coprecipitation, and stabilized by compound additions through appropriate techniques. And its mechanical property that is related to the phase content and its microstructure was studied by X-ray diffraction (XRD), scan electron microscope (SEM). The results show that Y2O3 has stronger inhibition to the growth of ZrO2 crystal than CeO2 has. Therefore, within an appropriate composition range of Y2O3 and CeO2, the higher the content of Y2O3, the lower the content of CeO2, the smaller ZrO2 crystal. Combining this feature and the stabilization technique with complex additions instead of simple addition, ZrO2 ceramic with high density and excellent mechanical properties can be made under normal conditions. It is concluded that the improvement of mechanical properties originates from the toughening of microcrack, phase transformation and the effect of grain evulsions.

Surface and Textural Properties of Network-Modified Silica as a Function of Transition Metal Dopant Zirconium

Surface and textural properties of Zr-doped silica [xZrO2-(100 − x)SiO2] have been investigated as a function of zirconium content in the range of x = 5 to 50 (mol % Zr) via heating their respective xerogels (prepared with a novel sol−gel route developed recently) in air at 500 °C for 4 h. Nitrogen adsorption−desorption investigations (BET/BJH) on the 500 °C-heated samples show a maximum specific surface area of 484 m2g-1 at x = 20, and a minimum of 105 m2g-1 at x = 50. With increase of zirconium content, porosity of the Zr-doped silica can be tuned conveniently from the mesoporous (100 Å) to the microporous (≤ 20 Å) region with unimodal (or nearly unimodal) pore size distributions. Material issues such as thermal reactions, oxide mixing level and formation mechanisms have also been investigated with FTIR, XRD, DTA/TGA, and XPS methods. It is found that silica networks have been significantly modified with the introduction of zirconium, and crystallization of ZrO2 in the doped silica occurs only at 903−953 °C. Moreover, surface analysis shows that there is no appreciable element enrichment in the surface region, whereas significant changes in binding energies of Zr 3d, Si 2p, and O 1s have been detected. The above observations are indications that a good mixing has been attained.