Advancement of High–k ZrO2 for Potential Applications: A Review

Metals

Monazite is one of the most valuable natural resources for rare earth oxides (REOs) used as dopants with high added value in ceramic materials for extreme environments applications. The complexity of the separation process in individual REOs, due to their similar electronic configuration and physical–chemical properties, is reflected in products with high price and high environmental footprint. During last years, there was an increasing interest for using different mixtures of REOs as dopants for high temperature ceramics, in particular for ZrO2-based thermal barrier coatings (TBCs) used in aeronautics and energy co-generation. The use of mixed REOs may increase the working temperature of the TBCs due to the formation of tetragonal and cubic solid solutions with higher melting temperatures, avoiding grain size coarsening due to interface segregation, enhancing its ionic conductivity and sinterability. The thermal stability of the coatings may be further improved by using rare earth ...

International Journal of Advanced Materials Manufacturing and Characterization, 2013

2014

The aim of this research was to get a product, partially stabilized zirconia. The powders of partially stabilized zirconia were prepared from zirconium tetrachloride and hydrated yttrium chloride precursors using a precipitation method. After drying and calcination, the powders were examined using X-ray diffraction. X-ray analysis shows that the powder dried at 120ºC is in amorphous phase, while upon calcination at 800ºC, it represents a partially stabilized zirconia with a presence of cubic and monoclinic phases. The basic purpose in preparing such mixtures was to obtain a finally-dispersed and homogenous powder which could be sintered at relatively low temperatures. From the super fine powder were prepared probes which were then dried at 120ºC and sintered at temperature of 1300ºC, for a period of 1 and 3 hours. Further analysis of the sintered probes showed density of 4.37 and 4.46 g/cm3. The X-ray analyses show that these probes are represented with 70% of cubic phase and 30% of monoclinic phase, thus concluding the partial stabilized zirconia. Probes sintered at 1300ºC were tested to the resistance to the thermal shocks. The probes were heated at 1300ºC, for the time of 5 minutes and after that cooled at 20ºC, for the same time. All probes endured 40 thermal shocks without appearance of cracks. The probes don’t change their phase content, and have high thermal stability.

The Journal of Physical Chemistry C, 2011

The phase stability and microstructure evolution of zirconia nanofilms on Si substrates prepared by ion beam assisted deposition (IBAD) upon thermal annealing and intensive radiation have been studied by in situ transmission electron microscopy (TEM), ex situ X-ray diffraction, and Raman spectroscopy. For as-prepared amorphous-dominant ZrO 2 thin films, a phase transformation sequence of amorphous-to-tetragonal and tetragonal-to-monoclinic has been identified upon increasing annealing temperature from 500, 850, to 1000°C. This phase transformation sequence varying with annealing temperature is accompanied by concomitant grain growth from ∼5 to ∼50 nm, consistent with the grain-size-controlled phase stability as a result of total energy crossover among different zirconia polymorphs. Upon ion bombardments of 350 KeV O þ and 1 MeV Kr 2þ at room temperature, a monoclinic-totetragonal phase transformation was observed in the monoclinic-dominant ZrO 2 . This monoclinic-to-tetragonal phase transformation may be attributed to the oxygen vacancy accumulation in ZrO 2 upon irradiation. Furthermore, both 1 MeV Kr 2þ and 350 KeV O þ bombardments on the amorphous-dominant ZrO 2 lead to an amorphous-to-tetragonal phase transformation as a result of radiation-induced recrystallization process. Thermodynamically metastable tetragonal ZrO 2 phase can be stabilized at room temperature under intensive radiation by relatively low-energy ion bombardments. These results suggest a method of combining both thermal annealing and ion beam technique for controlling ZrO 2 phase stability and thus tailoring materials properties for many engineering applications including actinide host matrix for advanced nuclear energy systems.

Zirconia - New Advances, Structure, Fabrication and Applications [Working Title]

Main resource of zirconia is the mineral zircon which occurs in beach sand and placer deposits. Alkali fusion and thermal plasma dissociation are the frequently adopted procedures to convert zircon to zirconia. Synthesis of different zirconia phases (monoclinic, cubic, and tetragonal) can be accomplished by the precise control of different operating parameters and stoichiometry of the reagents. Mesoporous and nano-zirconia which find wide application in catalysis and electronics are synthesized by different methods like solution combustion synthesis, sol–gel synthesis, hydrothermal synthesis, co-precipitation, and solid-phase sintering. Recently, biosynthesis of zirconia has taken a quantum leap due to environmental concerns. The synthesized zirconia is characterized by various chemical, physical, and instrumental methods to find out composition, crystal structure, size, and morphology.

Journal of Molecular Structure, 1999

Three different zirconia precursors were synthesized from zirconium(IV)-propoxide by sol-gel processing at pH 1.5, 5.5 and 10.5. The first crystallization products, obtained after the calcination of ZrO 2 precursors at 400ЊC, contained metastable t-ZrO 2 as a dominant phase. The sensitivities of metastable t-ZrO 2 products to the influence of temperature (600ЊCand 800ЊC) or pressure (500, 1000 and 1350 MPa) were monitored by laser Raman and FT-IR spectroscopies. X-ray powder diffraction was used as a complementary technique. It was found that the pH, used during the sol-gel processing of the ZrO 2 precursor strongly influenced the sensitivity of the metastable t-ZrO 2 products to the influence of temperature or pressure. The most stable t-ZrO 2 product was obtained from the ZrO 2 precursor precipitated at pH 1.5 and the most susceptible from the precursor precipitated at pH 5.5. ᭧

Journal of the American Ceramic Society, 2008

X-ray diffraction (XRD) and electron microscopy investigations have been performed on Sc 2 O 3-stabilized ZrO 2 as-sintered and after aging in air or in wet-forming gas at 8501C for 1000 h. Some tetragonal to monoclinic transformation had occurred in the near-surface regions of 4 mol% Sc 2 O 3 samples after aging; the phase transition was more severe for samples aged in the forming gas ambient. A decrease of B20% in electrical conductivity accompanied the aging. In 6 mol% Sc 2 O 3 samples, although no cubic to tetragonal transformation was detected, both the electrical conductivity and the activation energy for ionic conductivity decreased significantly during aging. Ten mole percent Sc 2 O 3 samples did not show appreciable change in electrical conductivity due to aging, although some near-surface cubic to rhombohedral transformation did occur. Sharpening of the (400) t XRD peak of Sc 2 O 3-stabilzed tetragonal ZrO 2 accompanies the change(s) in the electrical conductivity.

Journal of Sol-Gel Science and Technology, 2015

Yttria-stabilized zirconia (YSZ) has been studied as a promising material for application as an electrolyte in solid oxide fuel cells. In this work, YSZ powders ((xY 2 O 3-(1x)ZrO 2), x = 5, 8 and 10 mol%) were synthesized by three different methods: co-precipitation, sol-gel combustion and sol-gel. The precursor solution obtained by sol-gel method was successfully applied for chemical solution deposition of YSZ thin films on Si(100)/SiO 2 substrates. The thermal behavior of Y-Zr-O precursor gels and precipitated Y-Zr oxalates were investigated by TG-DSC measurements. X-ray diffraction analysis was utilized for the characterization of phase purity and crystallinity. Scanning electron microscopy was employed for the estimation of surface morphology features. The quality of obtained ceramic samples strongly depends on the morphology of initial powders. Electrical properties of synthesized ceramics were studied by means of impedance spectroscopy. The highest ionic conductivity was observed for samples prepared by sol-gel combustion synthesis route.

Microscopy and Microanalysis, 2013

As the presence of Sc2O3 and CeO2 is known to largely enhance the ionic conductivity in the temperature range of 600–800°C, compared with the conventional yttria-stabilized ZrO2, Sc2O3&CeO2-stabilized ZrO2 provide its applicability as electrolytes in solid oxide fuel cells. The current study introduces the methodology to synthesize Sc2O3&CeO2-stabilized ZrO2 powders by using co-precipitation technique or high-temperature hydrothermal reaction, and further describes the structural characterization of the zirconia powders synthesized by the above-mentioned two methods. The co-precipitation technique was found to allow obtaining powders of cubic phase, whereas high-temperature hydrothermal synthesis results in the presence of a monoclinic phase as well. The scanning transmission electron microscope observations also confirm that the size of the synthesized ZrO2 powders in this study is found to be much smaller than that of commercially available powders.

2014

The influence of low concentrations (1 mol %) of few co-dopants (Y2O3, La2O3, CeO2, Gd2O3, Er2O3, ZnO) on the structure and characteristic of 10 mol % scandia stabilized zirconia was studied. Sintering kinetics and thermal expansion coefficients of synthesized solid eletrolytes were determined. It was found that co-doping increased the conductivity of electrolytes at temperature below 550°C. However, at high temperatures, the introduction of co-dopants decreased the conductivity; moreover, this reduction was more severe the more the ionic radii of Zr4+ and co-dopant differ

Journal of Shanghai University (English Edition), 2006

Thermodynaufic assessment in the ternary systems ZrO=,-CeOe-Y~ O8, ZrO2-CeOe-Ce2 O3 and the limiting binaries ZrO2-Y203, ZrO2-CeOe. CeO2-Y2 O3, ZrO2-Ce~ O3, CeO2-Ce20:~ as well as the modeling for oxides are reviewed comprehensively. Based on the recent estimations on the YOI.5-CeOe, ZrO~-CeO2 and ZrO2-YO~ 5 systems, isothermal sections at 1 273 and 1 973 K of the ternary CeO2-ZrOe-YO~. 5 system are calculated. In the system of ZrOe-CeO2-Ce~O ~ , the complex relation between the nonstoichiometry (y) in CeO2 ~, the composition of the ZrOe -CeO~ solid solution and the oxygen partial pressure ( P% ) for different ZrO2 containing solid solutions Ce~ Zr~ _ ~ Oe ~ ~ are evaluated from 1 473 to 1 773 K. The relation between the degree of Ce + 4 reduction to Ce "3 under different Poe in the fluorite CeO2 y and Ce: Zr~ _ ~ O2 ~. solid solutions at different temperatures can be used as a guide in the development of functional ceramics.

MRS Proceedings, 1994

Zirconia and zirconia-yttria coating films and powders obtained by the sol-gel route using a zirconium alkoxide as starting material and acid and neutral catalytic were investigated by the Perturbed Angular Correlations method (PAC), XRD, DTA and TGA. The hyperfine interaction was measured either during heat treatements or after annealing the samples at increasing temperatures up to 1200'C. All samples have presented a high fraction of crystalline phases at low temperatures. The yttria doped cubic zirconia has not shown the phase transition to the monoclinic phase. Pure zirconia powders produced in neutral hydrolysis and zirconia coatings produced in acid catalysis stabilized the tetragonal phase in a high fraction and up to high temperatures.

Synthesis and Characterization of Gadolinium-Doped Zirconia as a Potential Electrolyte for Solid Oxide Fuel Cells, 2022

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Journal of Molecular Structure, 2011

In 2 O 3 X-ray diffraction Raman spectroscopy Electron microscopy DTA a b s t r a c t

Crystals

In this work, using a mechanochemical solid-phase synthesis method, ZrO2—CeO2 ceramics doped with yttrium were obtained, which have great prospects for use as a basis for dispersed nuclear fuel materials or inert nuclear fuel matrices. The purpose of this work was to study the formation of the ZrO2—CeO2 phase composition, depending on the concentration of yttrium dopant, as well as to study their structural and strength properties. The relevance of this study is in obtaining new data on the properties of composite ceramics based on oxides having a cermet structure, as well as the effect of doping with yttrium on increasing the resistance of ceramics to deformation and thermal properties. During the studies, the dynamics of the phase transformations depending on the concentration of the dopant, as well as changes in the structural characteristics and dislocation density, were established. It was found that at a dopant concentration of 0.25 mol, the main phase in the structure was Ce3...