ZrO2-Y2O3 System Research Articles

Lu2O3–Y2O3–ZrO2: A Lu3+ co-doped YSZ system—Oxygen-ion conductor with high electrical conductivity and improved mechanical properties

This study investigates the electrical and mechanical properties of a Lu2O3–Y2O3–ZrO2 system (ZrO2 co-doped with Lu2O3 and Y2O3) and evaluates its possibility for use as a high-performance oxygen-ion conducting ceramic suitable for intermediate/high-temperature solid electrolytes. The use of electrochemical impedance spectroscopy (EIS) in the analysis and fitting of AC impedance spectra arcs on 8 mol% (Lu2O3–Y2O3)– ZrO2 has allowed to compare with the Y2O3-doped ZrO2 (YSZ) and Sc2O3-doped ZrO2 (ScSZ). (ZrO2)0.92(Y2O3)0.07(Lu2O3)0.01, with 1 mol% Lu2O3 co-doped with Y2O3, shows a bulk conductivity of 9.60 × 10−1 S/cm at 1000 °C and 3.47 × 10−2 S/cm at 800 °C, which are least several times higher than the corresponding values of any other sample in the experimental group, including Sc2O3-doped ZrO2, over the entire measured temperature range. (ZrO2)0.92(Y2O3)0.075(Lu2O3)0.005 also shows an outstanding conductivity; over two times higher than that of ScSZ. Thus, Lu2O3 co-doping can enhance mechanical properties such as flexural strength (19.5 % (1 mol% Lu2O3) and 21.5 % (2 mol% Lu2O3) higher than that of YSZ), as confirmed by the flexural strength and Vickers hardness tests. After 8 mol% sesquioxide doping of YSZ, the maximum improvement in the electrical and mechanical properties occurs at approximately 1 mol% (for electrical properties) and 2 mol% (for mechanical properties) Lu2O3 co-doping, respectively. The results of this work suggest that a small amount of Lu doping, performed during the development of materials for use in electrochemical devices (including high-efficiency energy conversion apparatus), could be a considerable approach to overcome the limitations of conventional solid oxide electrolytes.

Phase diagrams of zirconium dioxide systems with yttrium and scandium oxides

The literature data on the study of phase equilibria in systems zirconia with yttria and scandia are analysed. Possible schemes of low-temperature phase equilibria in ZrO2-Y2O3 and ZrO2-Sc2O3 systems are presented taking into account the third law of thermodynamics. The coordinates of non-variant transformations in these systems are tabulated. A sign of non-equilibrium states is the observation of non-diffusion processes of ordering of solid solutions. The modified cryoscopy method is used to calculate the distribution coefficients of scandia and yttria during the crystallization of the ZrO2 melt. The possibilities for the existence of a set of ordered phases in the ZrO2-Y2O3 system and diffuse phase transition in the cubic modification of zirconia are discussed.

Comparative study of zirconia based powders prepared by co-precipitation and in a microreactor with impinging swirled flows

Mesoporous nanosized xerogels and powders in the system ZrO2–Y2O3 are obtained by two techniques, including co-precipitation of hydroxides and micromixing in a microreactor with impinging swirled flows (MRISF). The phase composition, surface characteristics, microstructure and textural features of the prepared xerogels and powders are studied. Compared with the conventional co-precipitation procedure, MRISF technique provides xerogels with improved performances, including significantly lower hydrodynamic diameter, ζ-potential and agglomeration of the particles, probably due to a reduced content of active centers on their surface and high level of shear stresses in the course of the synthesis. Furthermore, the developed MRISF is shown to provide a continuous high-throughput process advantageous in respect of easy numbering-up instead of the conventional scaling-up. Particularly, the lab-scale MRISF device used in this study affords a daily output of the slurry up to 8.5 m3 yielding 200–300 kg/day of the target nanosized particles.

Phenomena Occurring upon the Sintering of a Mixture of Yttria-Zirconia Nanometric Powder and Sub-Micrometric Pure Zirconia Powder.

Mixtures of powders essentially differing in their particle morphology and size were applied to prepare polycrystals in a Y2O3-ZrO2 system. An yttria–zirconia solid solution nanometric powder with a Y2O3 concentration of 3.5% was prepared by subjecting co-precipitated gels to hydrothermal treatment at 240 °C. The crystallization occurred in distilled water. The pure zirconia powders composed of elongated and sub-micrometer size particles were also manufactured through the hydrothermal treatment of pure zirconia gel, although in this case, the process took place in the NaOH solution. Mixtures of the two kinds of powder were prepared so as to produce a mean composition corresponding to an yttria concentration of 3 mol%. Compacts of this powder mixture were sintered, and changes in phase composition vs. temperature were studied using X-ray diffraction. The dilatometry measurements revealed the behavior of the powder compact during sintering. The polished surfaces revealed the microstructure of the resulting polycrystal. Additionally, the electron back scattering diffraction technique (EBSD) allowed us to identify symmetry between the observed grains. Hardness, fracture toughness, and mechanical strength measurements were also performed.

Structure of nanoparticles in the ZrO2-Y2O3 system, as obtained under hydrothermal conditions

Structure of nanoparticles in the ZrO2-Y2O3 system, as obtained under hydrothermal conditions

Comparative Study of Luminophores in the System ZrO2–Y2O3–Eu2O3 Obtained by Wet Mixing and Coprecipitation Followed by Microwave Treatment

It is shown that the high-temperature (1100°C) microwave treatment of the ZrO2–Y2O3–Eu2O3 luminophores obtained by wet mixing using zirconium oxochloride and yttrium acetate leads to a significant growth in the luminescence brightness that exceeds that of an industrial luminophore based on Y2O3 : Eu3+ by a factor of 1.75. For a luminophore with the identical composition obtained by the coprecipitation of hydroxides from a solution of the corresponding nitrates, a similar microwave thermal treatment leads to a sharp decrease in the brightness. The observed differences in the characteristics of the synthesized luminophores are compared to the changes in the functional composition of their surface and dispersity as a result of the microwave treatment.

Effect of the Phase Composition and Local Crystal Structure on the Transport Properties of the ZrO2–Y2O3 and ZrO2–Gd2O3 Solid Solutions

The results of investigating the crystal structure, ionic conductivity, and local structure of the (ZrO2)1 –x(Gd2O3)x and (ZrO2)1 –x(Y2O3)x (x = 0.04, 0.08, 0.10, 0.12, and 0.14) solid solutions are reported. The crystals are grown by directional crystallization of the melt in a cold container. The phase composition of the crystals is investigated by X-ray diffractometry and transmission electron microscopy. The transport characteristics are studied by impedance spectroscopy in the temperature range of 400 to 900°C. The local crystal structure is examined by optical spectroscopy. Eu3+ ions were used as a spectroscopic probe. The study of the local structure of the ZrO2–Y2O3 and ZrO2–Gd2O3 solid solutions revealed the features in the formation of optical centers, which reflect the character of localization of oxygen vacancies in the crystal lattice depending on the stabilizing oxide concentration. It is established that the local crystal environment of Eu3+ ions in the (ZrO2)1 –x(Y2O3)x and (ZrO2)1 –x(Gd2O3)x solid solutions is determined by the stabilizing oxide concentration and is practically independent of the stabilizing oxide type (Y2O3 or Gd2O3). The maximum conductivity at a temperature of 900°C is observed in the crystals with 10 mol % of Gd2O3 and 8 mol % of Y2O3. These compositions correspond to the t'' phase and are close to the interface between the cubic and tetragonal phase regions. It is found that in the ZrO2–Y2O3 system the highly symmetric phase is stabilized at a lower stabilizing oxide concentration than in the ZrO2–Gd2O3 system. The analysis of the data obtained makes it possible to conclude that, in this composition range, the concentration dependence of the ionic conductivity is mainly affected by the phase composition rather than the character of the localization of oxygen vacancies in the crystal lattice.

Influence of phase composition and local crystal structure on the transport properties of ZrO2−Y2O3 and ZrO2−Gd2O3 solid solutions

Abstract. The results of investigation of crystal structure, ion conductivity and local structure of solid solutions (ZrO2)1−x(Gd2O3)x and (ZrO2)1−x(Y2O3)x (x = 0.04, 0.08, 0.10, 0.12, 0.14). The crystals were grown by directional crystallization of the melt in a cold container. The phase composition of the crystals was studied by X−ray diffractometry and transmission electron microscopy. Transport characteristics were studied by impedance spectroscopy in the temperature range 400—900 °C. The local crystal structure was studied by optical spectroscopy. Eu3+ ions were used as a spectroscopic probe. The results of the study of the local structure of solid solutions of ZrO2—Y2O3 and ZrO2—Gd2O3 systems revealed the peculiarities of the formation of optical centers, which reflect the nature of the localization of oxygen vacancies in the crystal lattice depending on the stabilizing oxide concentration. It is established that the local crystal environment of Eu3+ Ions in solid solutions (ZrO2)1−x(Y2O3)x and (ZrO2)1−x(Gd2O3)x is determined by the stabilizing oxide concentration and practically does not depend on the type of stabilizing oxide (Y2O3 or Gd2O3). The maximum conductivity at 900 °C was observed in crystals containing 10 mol.% Gd2O3 and 8 mol.% Y2O3. These compositions correspond to the t′′−phase and are close to the boundary between the regions of the cubic and tetragonal phases. It was found that in the system ZrO2—Y2O3 stabilization of the highly symmetric phase occurs at a lower stabilizing oxide concentration than in the system ZrO2—Gd2O3. Analysis of the data obtained allows us to conclude that in this range of compositions the main influence on the concentration dependence of the ion conductivity has a phase composition, rather than the nature of the localization of oxygen vacancies in the crystal lattice.

Effect of oxygen vacancies on direct N2O decomposition over ZrO2-Y2O3 catalysts

ABSTRACTThe effect of oxygen vacancies on catalytic activity for direct N2O decomposition was demonstrated in Zr1−xYxO2−δ solid solutions with a fluorite-related structure. The fluorite-type structure was formed as samples with a small amount of Y3+ (0.05 ≤ x ≤ 0.19) and a large amount of Y3+ (x ≥ 0.80), leading to the generation of a C-type structure derived from the fluorite-type structure by removing a quarter of the oxide anions. The oxygen vacancies worked as N2O adsorption sites and catalytic active sites, with the highest activity realized by the YO1.5 catalyst with a C-type structure, which contained the largest number of oxygen vacancies in the ZrO2-Y2O3 system.

Thermodynamics and vaporization of ceramics based on the Y2O3-ZrO2 system studied by KEMS

The ceramics based on the Y2O3-ZrO2 system is promising for development of refractory materials including ultra-high temperature ceramics. In the present study the samples of the Y2O3-ZrO2 system were synthesized by the solid-state method. The vaporization processes and thermodynamic properties of the Y2O3-ZrO2 system were studied by the Knudsen effusion mass spectrometric method. The vapor composition, the YO, ZrO, ZrO2 and O partial pressures over the samples as well as the Y2O3 and ZrO2 activities of the Y2O3-ZrO2 system were determined at the temperature 2660 K. Thermodynamic properties (i.e. excess Gibbs energies) of the Y2O3-ZrO2 system obtained in the present study can be described in terms of the subregular solution model.

Regularities of formation of complex oxides with the fluorite structure in the ZrO2–Y2O3 system

The crystal and local structures of the complex oxides (1–x)ZrO2 ∙ xY2O3 (YSZ) (x = 0.08–0.40) prepared by precipitation from solutions of metal salts followed by heat treatment in air were comprehensively studied by X-ray diffraction and Raman spectroscopy. Despite the same crystal structure type of the YSZ powders (cubic system, space group \(Fm\overline 3 m\) (225)), there are differences in the local structure of the samples. Comparison of the Raman spectra recorded at different laser excitation wavelengths provided the conclusion that the peaks observed in the Raman spectra of the YSZ samples with high yttrium content (x = 0.18–0.40) are likely to be due to luminescence of the powders.

Stabilization of the fluorite phase in the ZrO2–Y2O3 system

The calculated and experimental vertical ZrO2–Y2O3 sections of the Zr–Y–O system are compared to find the region of a stable fluorite structure of yttrium-stabilized zirconia (YSZ). X-ray diffraction (XRD) and Raman scattering are used to study the crystal and local structures of mixed oxide 0.82ZrO2 · 0.18Y2O3 (18YSZ) powders prepared by isothermal annealing of a precursor precipitated from a salt solution. The formation of a fluorite-type fcc structure (space group $$Fm\overline 3 m$$ ) in the powders is detected by XRD. Raman scattering study of the local structure of the cubic 18YSZ powders revealed traces of the tetragonal phase in them.

Synthesis and study of mesoporous xerogels and nanopowders of a metastable solid solution 97ZrO2–3Y2O3 for the fabrication of catalyst substrates

The—technology of the liquid-phase synthesis of metastable phases in the ZrO2–Y2O3 system has been developed. Mesoporous xerogels with the specific surface area of ~350 m2/g and monophase nanopowders (5–10 nm) of the tetragonal solid solution (ZrO2)0.97(Y2O3)0.03 have been obtained and their structural peculiarities have been revealed. The efficiency of the suggested technology and good prospects of the synthesized ZrO2-based precursors in creating catalysts’ substrates have been demonstrated.

The crystallization of glasses of the MgO–Al_2O_3–SiO_2–TiO_2–ZrO_2–Y_2O_3 system and the nature of a new yttrium-containing crystalline phase

The crystallization processes of glass of the MgO–Al2O3–SiO2–TiO2–ZrO2–Y2O3 system, which is close in composition to cordierite, have been studied after heat treatment in the range 800–1300°C. X-ray phase analysis is used to detect a new yttrium-containing crystalline phase, x-ray microanalysis is used to determine its composition, and a model sample is synthesized. Indices are assigned to the diffractogram of the model sample, and the space group of the crystal symmetry is determined, along with the parameters and volume of its unit cell.

Structure and properties of ZrO2-Y2O3 and their change after low temperature annealing

The influence of low temperature annealing on the structure and properties of ZrO2-Y2O3 powder obtained by the chemical reverse precipitation method is studied. It is shown that the increase in annealing temperature leads to the decrease in the average size of particles, which initially represent porous agglomerates with a high specific surface, to the size of monolithic polydomain particles, the sizes of which are commensurable with the sizes of crystallites. The grain growth in the ZrO2-Y2O3 system during annealing is defined by surface diffusion.

Compositional Dependence of Phase Formation Mechanisms at the Interface Between Titanium and Calcia‐Stabilized Zirconia at 1550°C

ZrO2 samples with various CaO contents were fabricated by hot pressing, whereby CaO was dissolved by and/or reacted with ZrO2 to form a solid solution and/or CaZr4O9, respectively. After a reaction with Ti at 1550°C for 6 h in argon, the interfacial microstructures were characterized using X‐ray diffraction and analytical electron microscopy. Experimental results were very different from those found previously in the Y2O3–ZrO2 system. The 5 mol% CaO–ZrO2 sample was relatively stable due to the formation of a thin TiO layer acting as a diffusion barrier phase. However, α‐Ti(O), β′‐Ti (Zr, O), and/or Ti2ZrO were found in 9 or 17 mol% CaO–ZrO2 due to extensive interdiffusion of Ti, O, and Zr with a much thinner (β′‐Ti+α‐Ti) layer in 17 mol% CaO–ZrO2 than in 9 mol% CaO–ZrO2. Because CaO was hardly dissolved into Ti, it fully remained in the residual ZrO2, leading to the formation of spherical CaZrO3 in 9 mol% CaO–ZrO2 and columnar CaZrO3 in 17 mol% CaO–ZrO2. In the region far from the original interface, abundant intergranular α‐Zr was formed in 5 or 9 mol% CaO–ZrO2. Scattered α‐Zr and CaZrO3 were found in 17 mol% CaO–ZrO2 because a high concentration of extrinsic oxygen vacancies, which were created by the substitution of Ca+2 for Zr+4, effectively retarded the reduction of zirconia.

Effect of mechanochemical activation on the synthesis and sintering of solid solutions based on ZrO2

The effect of mechanochemical activation on the synthesis of tetragonal solid solutions in the systems ZrO2-Y2O3 and ZrO2-Y2O3-CeO2 and also the possibility of preparing the substances in amorphous and nanocrystalline states were studied.

Features of solid solution formation with a fluorite type structure in the system ZrO2-HfO2-Y2O3 with different synthesis methods

X-ray phase, petrographic, and thermal analysis methods are used to study the properties of solid solutions with a fluorite type structure in the ternary system ZrO2-HfO2-Y2O3 in relationship to preparation method: mixing of the original powders followed by solid-phase sintering and melting in solar furnaces; hydrothermal synthesis of nanocrystalline powders followed by solid-phase sintering. It is shown that in specimens whose composition lies at the isoconcentrate of 10 mole% Y2O3 a single phase forms independent of preparation method, i.e. a solid solution with a fluorite type structure. The azeotrope, situated at the liquidus of the limiting binary system ZrO2-Y2O3 in the region of fluorite-like solid solutions, affects the melting temperature of ternary solid solutions and the lattice parameters of specimens after melting in a solar furnace.

Electron Beam-Physical Vapour Deposition of Zirconia Co-Doped with Yttria and Niobia

Turbine blades of airplanes and thermoelectric plants work in adverse conditions, with corrosive environment and high temperature and pressure. One way to improve the life or the working temperature of the blades is by the use of special coatings over metallic material applied by Electron Beam – Physical Vapour Deposition (EB-PVD). The most usual material for this application is zirconia doped with yttria. Addition of niobia, as a co-dopant in the Y2O3-ZrO2 system, can reduce the thermal conductivity and improve mechanical properties of the coating. The purpose of this work is to show the influence of the addition of niobia on microstructure of ceramic coating taking in to consideration X-ray diffraction and scanning electron microscopy observations. First result shows a columnar structure with only tetragonal phase in the ceramic coating in the chemical composition range studied.

EB–PVD TBCs of zirconia co-doped with yttria and niobia, a microstructural investigation

Turbine blades of airplanes and thermoelectric plants work in adverse conditions, with corrosive environment and high temperature and pressure. One way to improve the life and/or the working temperature of the blades is the use of special coatings over metallic material applied by Electron Beam–Physical Vapor Deposition (EB–PVD). The most usual material for this application is yttria doped zirconia. Addition of niobia, as a co-dopant in the Y2O3–ZrO2 system, can reduce the thermal conductivity and improve mechanical properties of the coating. The purpose of this work is to show the influence of the addition of niobia on the microstructure of ceramic coatings by using X-ray diffraction (XRD) techniques and scanning electron microscopy (SEM) observations. SEM on fractured cross-section shows a columnar structure and the results of XRD show only zirconia tetragonal phase in the ceramic coating for the chemical composition range studied. As the difference (NbO2.5–YO1.5) mol% increases, the ratio c/a (tetragonality) increases. Considering that the t-ZrO2 solid solutions begins unstable when the relation c/a exceeds 1.020, it is possible to evaluate the maximum niobia content that can be added to the coating without losses in its mechanical properties. SEM on ceramic coatings polished cross-section shows color bands associated with chemical composition changes due to the differences in saturation vapor pressure of the individual components. As the niobia content increases, there is a tendency to reduction of the ceramic coating theoretical density.