High-pressure structural and lattice-dynamics study of Yttria-Stabilized Zirconia

TL;DR

The study tackles how YSZ doped with different Y2O3 contents responds structurally to high pressure. By combining in-situ XRD and RS in a diamond-anvil cell up to 40 GPa, the authors map the sequence of phase transitions for 3YSZ and 8YSZ, from monoclinic to tetragonal to t

Abstract

The structural evolution of two selected compositions of Yttria-Stabilized Zirconia (YSZ), with 3mol% (3YSZ) and 8mol% (8YSZ) of Y2O3, have been investigated under pressure using in-situ synchrotron X-ray diffraction (XRD) and Raman spectroscopy in a diamond anvil cell up to 40 GPa (at room temperature).The close crystallographic relation between the observed structures and the relatively large difference in the atomic numbers of Y/Zr and O, imposes the simultaneous study using both techniques, aiming to fully elucidate the structural evolution under pressure. The results, by combining both techniques, reveal that for both 3YSZ and 8YSZ, pressure promotes higher-symmetry structures. Under initial compression, the minority at ambient conditions monoclinic phase (m-phase) gradually transforms towards t-phase, a transition that is concluded for both 3YSZ/8YSZ at ~10 GPa. At higher pressures, the solely remaining t-phase of 3YSZ transforms to the t'', that in turns transforms to the c-phase above 28 GPa. Likewise, for 8YSZ the coexistence of t- and t''-phases continue up to 31 GPa, where both transforms towards c-phase, that remains stable up to the highest pressure of this study. Upon pressure release, all observed transitions are fully reversible with negligible hysteresis, with the exception of the practical disappearance of the monoclinic phase at ambient conditions. Our study underscores the significance of simultaneously performing and analyzing the results of both XRD and Raman spectroscopy studies in relevant crystallographic systems. Moreover, it provides a route towards a ``structural purification'' of YSZ through the elimination of the m-phase aiming to improve material properties.

Figures (9)

• Figure 1: Schematic representations of the monoclinic, tetragonal (t and t", in the cubic-like representation) and the cubic crystal structures of YSZ adopted from Yashima et al. Yashima1996. The arrows inside O atoms denote the displacement from the ideal (Fluorite-like) 1/4,1/4,1/4 positions. The relation between the tetragonal (black axes) and the distorted cubic fluorite-type (blue axes) crystal structures is also depicted.
• Figure 2: XRD patterns of (a) 3YSZ and (b) 8YSZ at ambient conditions compared with relevant previously reported structures for YSZLamas2000Tyrsted2014; see text for details. The downright arrows indicate the strongest Bragg peaks of the minority m-phase. The insets show an expanded view of the relevant patterns around 13$^{\circ}$ 2$\theta$ diffraction angle. (c) Raman spectrum of 8YSZ at ambient conditions, the asterisks denote most intense peaks of the m-phase. The inset shows the expected Raman spectra of the m- and t- phases of YSZ according to Ref. Hemberger2015.
• Figure 3: (a) XRD patterns for 3YSZ up to 30 GPa. (b) XRD patterns in the diffraction angle 2$\theta$ region of the [220]$_t$, [004]$_t$, [400]$_f$ reflections for 3YSZ up to 30 GPa.
• Figure 4: (a) XRD patterns for 8YSZ up to 40 GPa. The peaks marked with asterisks, squares and cycles originate from Re (gasket material), Au (pressure marker) and Ne (PTM), respectively (b) XRD patterns in the diffraction angle 2$\theta$ region of the [220]$_t$, [004]$_t$, [400]$_f$ reflections for 8YSZ up to 40 GPa.
• Figure 5: Raman spectra of 3YSZ upon (a) pressure increase from ambient to 40 GPa and (b) pressure decrease up to ambient pressure. In (a) the asterisks indicate the strongest Raman modes of the monoclinic phase Hemberger2015Loganathan2012torres2009. The downward and upward arrows correspond to the 4th and 6th peaks of the Raman spectrum of the t-phase, respectively, following Yashima et al.Yashima1993b analysis.