Electrolytic behavior of yttria and yttria stabilized Hafnia

Abstract

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Enthalpy of formation of cubic yttria-stabilized hafnia

“…The present calorimetric study and electrical conductivity studies 7,30 show that ordering is substantial in this system. Future solution models applied to this system should reflect this, and for the cubic fluorite phase, thermodynamic quantities are now constrained by the present calorimetric data (Table IV).…”

“…While the existence of short range order in the ZrO 2 -YO 1.5 system has been verified by direct observation, [26][27][28][29] the existence of short range order in the HfO 2 -YO 1.5 system has been inferred from electrical conductivity measurements. 7,30 In these studies, a maximum in conductivity is observed with doping level, and, as in the ZrO 2 -YO 1.5 system, this is ascribed to defect ordering. In the ZrO 2 -YO 1.5 system, the minimum doping level needed to stabilize the cubic phase in enthalpy with respect to the oxides m-ZrO 2 and C-type YO 1.5 corresponds to the maximum in conductivity at x ‫ס‬ 0.15.…”

Energetics of rare-earth-doped hafnia

“…In the fluorite solid solutions, this destabilization would be consistent with more negative heats of mixing (as observed), reflecting more extensive clustering and the preferential association of the oxygen vacancy with the tetravalent ion. 5,35 From these studies relating the radiation-resistance of pyrochlores, 12,27,28,[30][31][32][33][34] two conclusions were drawn: (i) systems in which a fluorite phase occurs (RE-zirconates) are more radiation resistant than systems in which only the pyrochlore phase occurs (RE-titanates and stannates), and (ii) systems with intermediate and small ions (GdLu) as a dopant are more radiation resistant than oxides with large dopant (La-Sm).…”

“…However, extensive short-range order in RE-doped hafnia with fluorite structure is proposed by several authors. 4,5 Quenchable HfO 2 -REO 1.5 solid solutions with fluorite structure are reported for the RE sequence from Sm to Yb. 6 The disordered fluorite-type structure is related to the pyrochlore structure (A 2 B 2 O 7 ), characterized by an ordered cation sublattice and ordered oxygen vacancies.…”

Thermochemistry of Lanthana‐ and Yttria‐Doped Thoria

“…In all trivalent-doped fluorite oxide ionic conductors, the ionic conductivity goes through a maximum or reaches a roughly constant value at some doping level within the solubility range, although the defect concentration continuously increases. [13][14][15][16] This phenomenon is associated with defect interactions that need to be understood in detail.…”