Phase equilibrium relationships in the system Gd2O3-TiO2

Waring, J.L.; Schneider, Samuel J

doi:10.6028/jres.069a.025

Cited by 42 publications

(21 citation statements)

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“…The Gd TiO line phase is formed at 50 at.% Ti>, and a small solid solution region with the Gd Ti O pyrochlore structure exists between 50 and 53 at.% Ti>, in agreement with the phase diagram by Waring and Schneider (14). The Gd TiO phase has unit cell parameters a"10.4788 A s , b"11.328 A s , and c"3.7547 A s .…”

Section: In the Zrosupporting

confidence: 68%

Phase Relations at 1500°C in the Ternary System ZrO2–Gd2O3–TiO2

Feighery

Irvine

Chang³

2001

Journal of Solid State Chemistry

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Phase relations at 15003 3C in the ternary system ZrO 2 +Gd 2 O 3 +TiO 2 have been determined by the powder X-ray di4raction of samples prepared by standard solid state reaction. A large area of this ternary oxide system centered on the Gd 2 Ti 2 O 7 +Gd 2 Zr 2 O 7 join was shown to exhibit the pyrochlore and defect 6uorite structures. The pyrochlore structure was observed for stoichiometries as far from the ideal M 4 O 7 as M 4 O 6.7 and M 4 O 7.4 , although the degree of disorder seemed much higher at these stoichiometries. On further deviation from the ideal M 4 O 7 stoichiometry a smooth transition to 6uorite average structure was observed for Zr-rich compositions. None of the other binary phases were observed to show signi5cant extent of solid solution into the ternary region. Academic Press INTRODUCTIONSolid oxide fuel cells are at the forefront of the search for more e$cient and environmentally friendly means of energy conversion because of their potential in combined heat and power generation from either hydrocarbon fuels or hydrogen. Most current development centers on designs based on the yttria-stabilized zirconia (YSZ) electrolyte, with Ni/YSZ cermets as the preferred anode (1). In the cermet anode materials, the YSZ provides the oxide ion conduction and the nickel provides the electronic conduction. This means that the electrochemical oxidation of the fuel gas can only occur at the triple points between the oxide ion conductor, the electronic conductor, and the fuel gas. The Ni/YSZ cermet has several other disadvantages including carbon deposition at the anode (2), the low tolerance of nickel to sulfur (3), and the sintering of the nickel on prolonged operation (4).Our objective has been to search for new candidate materials for SOFC anodes, and attention has been focused on the use of early transition metal oxides. Oxides have several advantages over metals, in that they are potentially less likely to promote coking, i.e., carbon buildup, and less likely to su!er from sulfur poisoning. Also, the accessibility of mixed valence states facilitates electronic conductivity and generally enhances catalytic activity. Thus in a mixed conducting anode the electrochemical reaction can occur over the entire electrode/gas interface as opposed to the three point contacts between the electrode, electrolyte, and fuel gas (5).In this study, we report the phase relations at 15003C in the ternary system ZrO }Gd O }TiO ; this temperature was chosen as it was the temperature used to synthesize these refractory oxides. Although 10003C might have been a more interesting temperature from a technological perspective it is very di$cult to attain thermodynamic equilibrium at this temperature. Previously the phase relations in this system have only been studied to a limited extent, particularly relating to the binary systems and the pseudobinary join Gd Zr \V Ti V O . The search for potential anode materials in this system has primarily been focused on the &&stoichiometric'' pyrochlore compositions in the system Gd Zr \V Ti V...

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Section: In the Zrosupporting

confidence: 68%

Phase Relations at 1500°C in the Ternary System ZrO2–Gd2O3–TiO2

Feighery

Irvine

Chang³

2001

Journal of Solid State Chemistry

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“…Another two partial diagrams [8,9] have been published for the ZrO 2 -rich corner at 1773 K (1500°C) and 1723 K (1450°C); both showed a similar maximum solubility of YO 1.5 and TiO 2 in tetragonal zirconia (~12 pct TiO 2 and 6 pct YO 1.5 ) and a F+T+Z three-phase field. Although the phase fields agree well with the other experimental diagrams, [4][5][6][7]10] the location of the phase boundaries varies considerably. In conclusion, there exists an urgent requirement to clear up the ambiguities in this system by the CALPHAD method and obtain a set of credible thermodynamic parameters for describing the phase relationships and thermodynamic properties of the ZrO 2 -TiO 2 -YO 1.5 ternary system.…”

Section: Survey Of Literature Informationmentioning

confidence: 56%

“…Feighery [6] published an experimental diagram at 1773 K (1500°C) and suggested a two-phase region of Y 2 Ti 2 O 7 and ZrTiO 4 , which is only presented in the diagram at 1573 K (1300°C) reported by Schaedler. [10] Moreover, no experimental findings confirmed that the rutile can directly reach equilibrium with the fluorite; it is inconsistent with the diagram reported by Kobayashi [7] and Yokokawa, [4,5] and both insisted that there exists a two-phase field between the rutile and the fluorite. Otherwise, Feighery's [6] diagram seems inconsistent with the phase rule.…”

Section: Survey Of Literature Informationmentioning

confidence: 73%

“…Yokokawa [4,5] used the reported thermodynamic data of ZrO 2 to estimate other oxides based on the correlations between the interaction parameters and the ionic radii and calculated the isothermal section of the ZrO 2 -TiO 2 -YO 1.5 system at 1573 K (1300°C). According to the phase equilibria calculated by Yokokawa, [4,5] there does not exist a two-phase region between Y 2 Ti 2 O 7 pyrochlore and ZrTiO 4 , which contradicts the experimental diagram published by Schaedler. [10] Schaedler [10] finished a very exhaustive review of the experimental data and systematically studied the whole phase field in the range of 1573 K to 1873 K (1300°C to 1600°C) using some necessary experiments.…”

Section: Survey Of Literature Informationmentioning

confidence: 99%

“…For example, (1) the tetragonal compositions in the zirconia-rich corner of the ZrO 2 -YO 1.5 -TiO 2 system possess a potential for enhancing the toughness of the general thermal barrier oxide of the ZrO 2 -YO 1.5 system, [2] (2) the region in the ZrO 2 -YO 1.5 -TiO 2 system concerning Zr +4 substitution for Ti +4 and Y +3 in the Y 2 Ti 2 O 7 pyrochlore may lead to a defect fluorite structure and a substantial increase in the ionic conductivity, [3] and (3) the extension in the homogeneity range of the fluorite phase with the increase of temperature brings about the possibility of designing refractories for melting titanium alloys. Although there is so much technological interest in the ZrO 2 -YO 1.5 -TiO 2 system, the inadequate and even selfcontradictory information [4][5][6][7][8][9][10] related to the phase equilibria and thermodynamic properties of the ternary system has become an obstacle to its practical application. Recently, Schaedler [10] experimentally investigated the phase relationship of the isothermal sections at 1573 K, 1773 K, and 1873 K (1300°C, 1500°C, and 1600°C) using prealloyed powders prepared by reverse co-precipitation, in which the samples after prolonged heat treatment could reach the real phase equilibria; this may imply that the phase diagram proposed by Schaedler [10] is more credible than the previous.…”

Section: Introductionmentioning

confidence: 99%

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Thermodynamic Modeling of the ZrO2-YO1.5-TiO2 System

Wang

Dong

et al. 2010

Metall Mater Trans A

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The binary systems ZrO 2 -YO 1.5 , ZrO 2 -TiO 2 , and YO 1.5 -TiO 2 are reassessed, and a set of self-consistent thermodynamic parameters, which can be reliably extrapolated into the ZrO 2 -YO 1.5 -TiO 2 ternary system, are obtained. The substitutional solution model and the stoichiometric compound model are applied to the phase description in the ternary system, and the thermodynamic database of this ternary system is derived by the CALPHAD approach. It is noted that, except for the liquid phase, no ternary interaction parameters are introduced. The present evaluation can better describe the experimental phase diagrams reported recently at 1573 K, 1773 K, and 1873 K (1300°C, 1500°C, and 1600°C). Thus, the optimized thermodynamic parameters may be authentic and can be applied to optimizing the compositions of the novel materials based on this ternary system.

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