2015 GSA Annual Meeting in Baltimore, Maryland, USA (1-4 November 2015)

Paper No. 16-10
Presentation Time: 10:55 AM

EFFECTS OF IRRADIATION-INDUCED STRUCTURAL DISORDERING IN ZIRCONATE PYROCHLORES AT HIGH PRESSURES


PARK, Sulgiye, Geological Sciences, Stanford University, 367 Panama St, Stanford, CA 94305, sulgiye@stanford.edu

Subsequent effects of high pressure on zirconate pyrochlores (A2Zr2O7, where A = Nd, Er, and Sm) are investigated after the materials had been disordered from swift heavy ion irradiation. The motivations behind the study are that: 1) disordering induced by ion irradiation reduces the activation energy for anion vacancy migration, and the enhanced oxygen diffusion alters the pressure transition point of the material; and 2) a subsequent effect of pressure on ion-irradiated materials provides a unique way of creating a non-equilibrium states of matter, which can potentially yield a novel phase.

The study finds that the critical pressure transition point (crystalline to amorphous) of zirconate pyrochlores decreases by ~ 15 ± 4% after they had been disordered. This can be attributed to the bigger unit-cell volume of the ordered-pyrochlore structure, which allows more free space for compression. Ion irradiation also increases the coordination number around the B-site cation, which enhances the phase transition with increased pressure. For Er2Zr2O7, where the material initially has a disordered-fluorite structure from its small cation ionic radii ratio, rA/rB = 1.33, a reverse outcome is noticed i.e., the pressure transition point increases by ~ 5%. The increased compressibility may be due to the defects induced by swift heavy ions. A novel X-phase appears with high pressure in irradiated Nd2Zr2O7. The phase is determined to be similar to the Nd2O3 phase, and is comparable to that found in the previous study where an energetic ion irradiation was performed simultaneously with high pressure experiment. Although the X-phase is not quenchable, this study demonstrates that such a phase is accessible even without having to perform a simultaneous irradiation and pressure experiment.