Deformation Behavior across the Zircon-Scheelite Phase Transition

The pressure effects on plastic deformation and phase transformation mechanisms of materials are of great importance to both Earth science and technological applications. Zircon-type materials are abundant in both nature and the industrial field; however, there is still no in situ study of their deformation behavior. Here, by employing radial x-ray diffraction in a diamond anvil cell, we investigate the dislocation-induced texture evolution of zircon-type gadolinium vanadate (${\mathrm{GdVO}}_4$) in situ under pressure and across its phase transitions to its high-pressure polymorphs. Zircon-type ${\mathrm{GdVO}}_4$ develops a (001) compression texture associated with dominant slip along $⟨100⟩\{001\}$ starting from 5 GPa. This (001) texture transforms into a (110) texture during the zircon-scheelite phase transition. Our observation demonstrates a martensitic mechanism for the zircon-scheelite transformation. This work will help us understand the local deformation history in the upper mantle and transition zone and provides fundamental guidance on material design and processing for zircon-type materials.

Figure 1

Crystal structures and fitting example of ${\mathrm{GdVO}}_4$. (a) Zircon, (b) scheelite, and (c) $M$-fergusonite phases. The zircon phase begins to transform to a scheelite phase below 5 GPa. The transition is complete at 23 GPa. A subsequent transformation to an $M$-fergusonite phase occurs at 31 GPa. (d) Fitting example at 11 GPa. The bottom half of the pattern is the experimental data, and the top is the calculated pattern from the Rietveld refinement. The chi square (${\chi }^2$) is 1.071. Some of the diffraction lines from the zircon and scheelite phases are labeled (“$z$” for zircon and “$s$” for scheelite). Others are not labeled due to multiple peak overlaps between the two phases. The green arrows indicate the compression direction.

Figure 2

Refinement results for ${\mathrm{GdVO}}_4$ under pressure. (a) Volume fraction, (b) unit-cell parameters, (c) unit-cell volume (dashed lines are EOS fitting results), and (d) $t/G$ ratio of the zircon and scheelite phases as a function of pressure. The average values of $t/G$ shown in (d) are weighted means of those measured in both phases, $t$ is the differential stress, and $G$ is the shear modulus. For the $M$-fergusonite phase, only the volume fraction is shown.

Figure 3

Texture evolution of ${\mathrm{GdVO}}_4$ through the phase transition. Inverse pole figures of the compression direction are shown up to 23 GPa for both the zircon and scheelite phases. For each case, the experimental pressure and phase proportions are shown in the figure. Pole densities are measured in multiples of a random distribution (mrd). Equal area projections.

Figure 4

Dominate slip systems for the zircon phase under plastic deformation. (a) Slip systems reported in the literature. (b) Inverse pole figures calculated from seven VPSC models. The corresponding slip system activities for each model are shown in Table 1. Pole densities are in mrd. Equal area projections.