Properties Of Cubic Zirconia Research Articles

Electronic, optical and elastic properties of cubic zirconia (c-ZrO2) under pressure: A DFT study

The pressure induced theoretical investigations of electronic, optical and elastic constants of cubic zirconia (c-ZrO2) are estimated under the effect of hydrostatic pressure (0–40 GPa) by employing first principles based local density approximation (LDA) functional within the framework of density functional theory (DFT). The optimized structural parameters are in excellent agreement with previous theoretical and experimental values. Our calculated bandgap (3.350 eV) at zero pressure shows excellent consistency with previous listed computational results and very favorable approach to experimentally reported bandgap (4.6 eV) with the increment of pressure. Density of states (DOS) predicts dominant contribution of oxygen electrons of 2p-orbital and zirconium electrons of 4d-orbital in valence and conduction band formation. The estimated values of dielectric constant (5.85) and refractive index (2.42) at zero pressure are in good agreement with existing theoretical data. The optical constants are less sensitive to applied pressure and offer significant stability under high pressure. Pressure based elastic parameters exhibit high mechanical stability, more hardness and stiffness, improved ductility and higher elasticity of c-ZrO2 under high pressure.

Density functional theory of cubic zirconia and 6–15 mol% doped yttria-stabilized zirconia: structural and mechanical properties

Results of ab-initio density-functional theory calculations within the generalized gradient approximation (GGA-PBE) of structural and mechanical properties of cubic zirconia and yttria-stabilized zirconia (YSZ) with yttria (Y 2 role=presentation> 2 2 _{2} O 3 ) role=presentation> 3 ) 3 ) _{3}) concentrations of 6.67, 10.34, and 14.28 mol% are reported. It is found that the calculated structural and mechanical parameters of all considered structures are highly consistent with the existing experimental data and the other theoretical values. The doping concentration of yttria-stabilized zirconia has critical importance in ionic conductivity and stabilization of high temperature down to room temperature. The lattice parameter and cell volume linearly decrease with increases in doping concentration. Moreover, the effects of doping of yttria-stabilized zirconia on elastic constants are studied. Elastic constants of cubic zirconia and 6-15 mol% doped yttria-stabilized zirconia are calculated using the strain-stress approach and linear response theory.

Possible Origin of Ferromagnetism in Transition Metal Doped Zirconia

We have studied the electronic structure and magnetic properties of cubic zirconia (c-ZrO2) with cobalt (Co) or nickel (Ni) doping using density functional theory (DFT) calculations. The pure c-ZrO2 is a nonmagnetic insulator with a wide bandgap. The calculated results reveal that isolated Co or Ni atom can both produce the local magnetic moment in c-ZrO2. And the isolated Co atom can introduce a magnetic moment of about 0.98 μ B, while the Ni atom is 2.85 μ B. The impurity peaks can be formed in the bandgap. Our studies show that the magnetic moments mainly result from d orbitals of the impurity atoms. And the spin-up electrons will be arranged in t 2g orbitals under the ligand field of O h group in Co- or Ni-doped c-ZrO2. Obviously, this will lead to a high-spin state (S = 1/2 or 1). The studies of magnetic coupling reveal that the two Co atoms in c-ZrO2 are not always coupled ferromagnetically at different distances. And the system will be in a spin singlet state (S = 0) when the distance is 6.209 or 7.170 A between two Co atoms. However, the two Ni atoms in c-ZrO2 are always coupled ferromagnetically at all distances. So we can conclude that the Ni-doped c-ZrO2 is more suitable for spintronic material than Co doping. These results are significant for spintronics.

First-Principles Calculations of the Structural, Mechanical and Thermodynamics Properties of Cubic Zirconia

The structural, mechanical and thermodynamics properties of cubic zirconium oxide (cZrO2) were investigated in this study using ab initio or first-principles calculations. Density functional theory was used to optimize the crystal structure of cZrO2 and thereafter, simulations were conducted to predict the lattice parameters and elastic constants. The Zr-O bond distance was calculated as 2.1763 &#197 with unit cell density of 6.4179 g/cm3. The data obtained were used to determine Young’s modulus, bulk modulus, Poisson’s ratio and hardness of cZrO2 as 545.12 GPa, 136.464 GPa, 0.1898 and 12.663(Hv) respectively. The result indicates that cZrO2 is mechanically stable with thermodynamics properties of a refractory material having potential for structural and catalytic applications in various forms as a nanomaterial.

Modelling the Elastic Constants of Cubic Zirconia Using Molecular Dynamics Simulations

Analysis of structural and mechanical properties of cubic zirconia was conducted using a simulation code (GULP) that is based on the concept of energy minimization. Some mechanical properties of zirconia were computed such as elastic constant tensors, shear modulus, bulk modulus, Youngs modulus and others along the lattice planes. The stiffness constants obtained (C11, C22 and C33) were equal, implying that zirconia is flexible in all directions of the lattice plane. The predicted bulk modulus was 285 GPa with the shear modulus ranging between 78 and 105 GPa. The Youngs modulus of 577 GPa indicates higher ductile behavior as confirmed by the compressibility of 0.0035. The Poissons ratio with values ranging from 0.16 to 0.31 may indicate high anisotropy. Other acoustic features related to mechanical properties of zirconia such as velocity wave ratio, stress matrix dielectric constants and others were also analyzed. All estimations obtained show good agreement to recent measured properties of zirconia.

Microstructural and Mechanical Properties of Er2O3-ZrO2 Ceramics with Different Er2O3 Contents

AbstractIn this study, the effect of erbium oxide (Er2O3) addition on the microstructure, sinterability and mechanical properties of cubic zirconia (c-ZrO2) was investigated. 0–15 wt% Er2O3 and c-ZrO2 powders were mixed by means of colloidal processing and the specimens were sintered at different temperatures for 1 hour. The XRD results showed the existence of cubic crystal structure in all specimens. The lattice parameter of the specimens decreased with increasing Er2O3 addition up to 10 wt% and remained unchanged after this amount. The grain size of the Er2O3 doped c-ZrO2 specimens dropped up to 5 wt% Er2O3 addition and stayed almost unchanged at higher Er2O3 contents. Both hardness and fracture toughness measurements were done using Vickers hardness tester. The fracture toughness values of the undoped, 1, 5, 10 and 15 wt% Er2O3 doped c-ZrO2specimens were found to be 1.64 MPam1/2, 1.77 MPam1/2, 2.06 MPam1/2, 2.57 MPam1/2 and 2.31 MPam1/2 respectively.

Micro-structural evolution of cubic zirconia irradiated with swift heavy ions

This article deals with the study of the micro-structural properties of cubic zirconia irradiated with swift heavy ions, based on the combination of complementary analysis techniques (TEM, AFM, XRD, RBS/C). At low irradiation fluences, cross-sectional TEM observations show the creation of latent tracks in the wake of incident ions by electronic excitation processes. The melt matter flowing from ion tracks leads to the formation of large hillocks at the surface of samples revealed by AFM. At high irradiation fluences, the overlapping of tracks results in the subdivision of crystals into slightly disoriented nano-crystallites detected by XRD. RBS/C data analyzed with a Monte-Carlo simulation code confirm the occurrence of this peculiar micro-structural transformation.

Mechanical properties of cubic zirconia irradiated with swift heavy ions

The modifications of the mechanical properties of cubic (yttria-stabilized) zirconia induced by swift heavy ion irradiation are investigated. Polycrystalline pellets were irradiated at room temperature with 940 MeV Pb ions at the GANIL accelerator in Caen at fluences ranging from 5 × 10 11 to 4 × 10 13 cm −2. The microhardness and the fracture toughness of irradiated YSZ were studied by Vickers micro-indentation. Although YSZ is damaged by irradiation, an increase of the microhardness and fracture toughness with increasing ion fluence is observed. A strengthening of YSZ, associated with residual compressive stresses induced in the surface layer by irradiation, explain these results.

Sintering, phase stability and room temperature mechanical properties of c-ZrO 2 ceramics with TiO 2 addition

An investigation has been carried out into the effect of TiO 2 addition on the sintering, phase stability and room temperature mechanical properties of cubic zirconia (c-ZrO 2). c-ZrO 2 specimens containing TiO 2 addition up to 10 wt% were produced by colloidal processing and pressureless sintering. The sintered density of the specimens decreased with increasing TiO 2 content up to 1 wt% and further increase in TiO 2 content led to a increase in the sintered density. XRD results showed that when the TiO 2 amount was less than 5 wt%, the specimens were entirely single cubic phase; further addition of TiO 2 (5 wt% or more) destabilized cubic zirconia phase and caused the formation of tetragonal phase. The amount of tetragonal phase increased with increasing TiO 2 content in c-ZrO 2 matrix. The room temperature mechanical properties of flexural strength and fracture toughness both increased with increasing TiO 2 content.

Electronic Structure and Dielectric Properties of Cubic Zirconia

The electronic structure and dielectric properties of cubic zirconia (ZrO2) are investigated by the linear muffin-tin orbital method. The band structure and density of states of ZrO2 are calculated by the local density approximation and GW approximation. The band gap calculated by the GW approximation is 5.3 eV, which is close to the measured value. The dielectric function and the electron energy loss spectrum (EELS) of ZrO2 are also calculated and compared with experimental results. The dielectric function is analyzed and assigned in detail by decomposing the spectrum into individual peaks. The possibility of further improvement of the EELS is also discussed using the band structure of ZrO2 determined by the GW approximation.

Preparation of Fine Alumina Dispersed Ytterbia-Stabilized Cubic Zirconia Based Composites

To improve low mechanical properties of cubic zirconia, Al 2 O 3 has been dispersed to Yb 2 O 3 stabilized ZrO 2 (YbSZ). YbSZ/Al 2 O 3 nanocomposite powders were prepared by solution chemistry route, and sintered bodies were fabricated by pressureless sintering. Obtained composites have finer matrix grains with increasing Al 2 O 3 addition. The fracture strength of composites was remarkably increased due to the refinement of YbSZ matrix grain size. Ionic conductivity of composite at high temperatures was almost the same value of the monolithic YbSZ ceramic.

Thermal radiation and optical properties of cubic zirconia stabilised with yttria up to the temperature of high rate evaporation

The normal-hemispherical reflectivity at the wavelengths of 0.488, 0.6328, 1.15, and 3.39 μm of cubic zirconia ceramics stabilised with 8 mol% yttria was measured in the course of rapid heating in air by concentrated CO 2 laser radiation from room temperature to 3200 K and in the process of subsequent rapid cooling when the heating radiation was switched off. The results are presented and analysed. It is shown that, in the entire studied spectral range, with a molten layer 250-500 μm thick on the surface, an optically infinite layer is realised in the melt, and the reflection is mainly defined by the refractive index. This layer remains optically infinite just after solidification; however, by the end of the solidification process its reflectivity increases slightly owing to cracks and pores. Measurement of the reflection under prolonged stepwise heating by laser radiation fluxes of relatively low intensity and in the course of subsequent cooling provides data on spectral reflectivity under conditions close to isothermal. Some estimates for the absorption coefficient of the melt are given.

Synthesis and properties of cubic zirconia–alumina composite by mechanical alloying

Synthesis of 8mol%Y 2O 3–ZrO 2 (8YSZ) powder with Al 2O 3 by mechanical alloying (MA) and the sintering behavior of this powder were investigated. The solubility of Al 2O 3 in 8YSZ was 1.15 wt.% after MA for 48 h. Large agglomerated particles formed during MA resulted in a slow densification rate of the compact. After eliminating the agglomerates by sedimentation, the relative density of 97% was obtained by sintering the compact at 1400°C for 2 h. Sintered microstructure of mechanically alloyed 3wt.%Al 2O 3–8YSZ (3A8YSZ) consisted of 8YSZ grains in the size range of 0.5–1.2 μm and 20–400 nm size Al 2O 3 particles dispersed uniformly in the 8YSZ. Fracture toughness and hardness of the composite was improved due to intragranular dispersion of Al 2 O 3 particles. Electrical conductivity of the composite was 6.4×10 −5 S cm −1 at 400°C and also exhibited significant increase over monolithic 8YSZ. Improvement in lattice conductivity was unique in this composite and attributed to the role of intragranular Al 2O 3 particles, which provided strong lattice distortion of 8YSZ matrix.

Microstructure and mechanical properties of cubic zirconia (8YSZ)/SiC nanocomposites

The mechanical properties of cubic zirconia (8YSZ)/SiC “nanocomposites” were studied. These properties were found to be strongly dependent on the microstructure and processing conditions. For nanocomposites with SiC particles mostly inside the zirconia grains the bending strength, toughness and hardness were similar to that of monolithic 8YSZ. For nanocomposites with SiC particles located mainly on the grain boundaries, an improvement of the strength and an increase of the toughness were observed. The increase in strength is strongest at room temperature and decreases with rising temperature; the strengths of all materials are identical at ∼750°C. The higher strength cannot be completely accounted for by the observed increase in toughness, implying a reduced critical flaw size in the stronger material.

Electronic structure and optical properties of zirconia

The effects of substitutional impurities and oxygen vacancies on the electronic structure and optical properties of cubic zirconia were studied using band-structure calculations. It is shown that oxygen vacancies produce additional states near the Fermi level, whereas impurity atoms make an insignificant contribution to the states in the valence band and at the bottom of the conduction band, and their effect has a predominantly electrostatic character. The mechanisms of the stabilization of the high-temperature ZrO2 polymorphs are elucidated. The calculation results agree well with x-ray photoelectron spectroscopy and optical data