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Fast ion conductivity in strained defect-fluorite structure created by ion tracks in Gd2Ti2O7.

ABSTRACT: The structure and ion-conducting properties of the defect-fluorite ring structure formed around amorphous ion-tracks by swift heavy ion irradiation of Gd2Ti2O7 pyrochlore are investigated. High angle annular dark field imaging complemented with ion-track molecular dynamics simulations show that the atoms in the ring structure are disordered, and have relatively larger cation-cation interspacing than in the bulk pyrochlore, illustrating the presence of tensile strain in the ring region. Density functional theory calculations show that the non-equilibrium defect-fluorite structure can be stabilized by tensile strain. The pyrochlore to defect-fluorite structure transformation in the ring region is predicted to be induced by recrystallization during a melt-quench process and stabilized by tensile strain. Static pair-potential calculations show that planar tensile strain lowers oxygen vacancy migration barriers in pyrochlores, in agreement with recent studies on fluorite and perovskite materials. In view of these results, it is suggested that strain engineering could be simultaneously used to stabilize the defect-fluorite structure and gain control over its high ion-conducting properties.

SUBMITTER: Aidhy DS

PROVIDER: S-EPMC4639808 | biostudies-literature | 2015 Nov

REPOSITORIES: biostudies-literature

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Fast ion conductivity in strained defect-fluorite structure created by ion tracks in Gd2Ti2O7.

Aidhy Dilpuneet S DS Sachan Ritesh R Zarkadoula Eva E Pakarinen Olli O Chisholm Matthew F MF Zhang Yanwen Y Weber William J WJ

Scientific reports 20151110

The structure and ion-conducting properties of the defect-fluorite ring structure formed around amorphous ion-tracks by swift heavy ion irradiation of Gd2Ti2O7 pyrochlore are investigated. High angle annular dark field imaging complemented with ion-track molecular dynamics simulations show that the atoms in the ring structure are disordered, and have relatively larger cation-cation interspacing than in the bulk pyrochlore, illustrating the presence of tensile strain in the ring region. Density f ...[more]

PMID: 26555848

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Project description:Sm2-xCaxZr2O7-x/2 (x = 0, 0.05, 0.1) and Gd2-xCaxZr2O7-x/2 (x = 0.05, 0.1) mixed oxides in a pyrochlore-fluorite morphotropic phase region were prepared via the mechanical activation of oxide mixtures, followed by annealing at 1600 °C. The structure of the solid solutions was studied by X-ray diffraction and refined by the Rietveld method, water content was determined by thermogravimetry (TG), their bulk and grain-boundary conductivity was determined by impedance spectroscopy in dry and wet air (100-900 °C), and their total conductivity was measured as a function of oxygen partial pressure in the temperature range: 700-950 °C. The Sm2-xCaxZr2O7-x/2 (x = 0.05, 0.1) pyrochlore solid solutions, lying near the morphotropic phase boundary, have proton conductivity contribution both in the grain bulk and on grain boundaries below 600 °C, and pure oxygen-ion conductivity above 700 °C. The 500 °C proton conductivity contribution of Sm2-xCaxZr2O7-x/2 (x = 0.05, 0.1) is ~ 1 × 10-4 S/cm. The fluorite-like Gd2-xCaxZr2O7-x/2 (x = 0.1) solid solution has oxygen-ion bulk conductivity in entire temperature range studied, whereas proton transport contributes to its grain-boundary conductivity below 700 °C. As a result, of the morphotropic phase transition from pyrochlore Sm2-xCaxZr2O7-x/2 (x = 0.05, 0.1) to fluorite-like Gd2-xCaxZr2O7-x/2 (x = 0.05, 0.1), the bulk proton conductivity disappears and oxygen-ion conductivity decreases. The loss of bulk proton conductivity of Gd2-xCaxZr2O7-x/2 (x = 0.05, 0.1) can be associated with the fluorite structure formation. It is important to note that the degree of Ca substitution in such solid solutions (Ln2-xCax)Zr2O7-δ (Ln = Sm, Gd) is low, x < 0.1. In both series, grain-boundary conductivity usually exceeds bulk conductivity. The high grain-boundary proton conductivity of Ln2-xCaxZr2O7-x/2 (Ln = Sm, Gd; x = 0.1) is attributable to the formation of an intergranular CaZrO3-based cubic perovskite phase doped with Sm or Gd in Zr sublattice.

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Fast ion conductivity in strained defect-fluorite structure created by ion tracks in Gd2Ti2O7.

Publications

Fast ion conductivity in strained defect-fluorite structure created by ion tracks in Gd2Ti2O7.

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