Recovery of a high-pressure phase formed under laser-driven compression

The recovery of metastable structures formed at high pressure has been a long-standing goal in the field of condensed matter physics. While laser-driven compression has been used as a method to generate novel structures at high pressure, to date no high-pressure phases have been quenched to ambient conditions. Here we demonstrate, using in situ x-ray diffraction and recovery methods, the successful quench of a high-pressure phase which was formed under laser-driven shock compression. We show that tailoring the pressure release path from a shock-compressed state to eliminate sample spall, and therefore excess heating, increases the recovery yield of the high-pressure $\omega$ phase of zirconium from 0% to 48%. Our results have important implications for the quenchability of novel phases of matter demonstrated to occur at extreme pressures using nanosecond laser-driven compression.

Figure 1

(a) Experimental setup at MEC. An intense laser pulse drove an ablatively driven shock wave into the target package, which consisted of a polyimide ablator bonded to a polycrystalline Zr foil. The sample was probed by the collimated LCLS x-ray beam and scattered diffraction data were collected in a transmission geometry. The Zr free surface velocity history was recorded by the velocity interferometry (VISAR) diagnostic. (b) Typical raw VISAR data with the analyzed velocity profile overlaid. (c) Typical 2D diffraction data, with diffraction maxima warped into lines of constant $2\theta$, with the corresponding, azimuthally integrated 1D diffraction profile overlaid. Shading under the peaks refers to the identified phase (see Fig. 2).

Figure 2

(a) Waterfall plot of diffraction data collected at MEC after shock breakout and subsequent rapid pressure release from 22 GPa. The time in each case indicates the XFEL delay time relative to shock breakout at the Zr free surface. Specific diffraction peaks from the $\alpha$ phase (blue), $\omega$ phase (red), and corrundum phase from the ablator (green) are labeled. (b) Relative volume fraction of the $\alpha$ (blue symbols) and $\omega$ (red symbols) phases as a function of the time after shock breakout. When releasing from a free surface, the Zr sample, initially in the $\omega$ phase, undergoes full reversion to the $\alpha$ phase within 250 ns. The transformation rate is fit well with an exponential decay/growth (solid lines). (c) Volume expansion of the sample as a function of the time after shock breakout (symbols) and corresponding deduced temperature (solid lines). The Zr sample temperature is determined to exceed 2000 K on release, significantly hotter than the corundum ablator, due to the occurrence of spall and fracture of the Zr sample.

Figure 3

(a) Target design for recovery experiments at the Jupiter Laser Facility. The dashed line indicates that in some cases a high-impedance LiF tamper was used. (b) Photograph of recovered Zr material which had been collected in the sample recovery gel. Multiple spall events resulted in an average Zr particle size of $\sim 10$ $\mu \mathrm{m}$. Postshot diffraction measurements of this material showed only diffraction from the $\alpha$-Zr phase, consistent with the MEC experiments. Raw 2D diffraction data are shown with the azimuthally integrated profile overlaid. (c) Postshot photograph of the recovered Zr material which released into a LiF window. Profilometry measurements of the intact foil show that the shocked region was 1 mm in diameter and had a depth of 40 $\mu \mathrm{m}$. Raw 2D diffraction data are shown with the azimuthally integrated profile overlaid. A two-phase Reitveld refinement of these diffraction data showed that the volume fractions of the $\omega$-Zr (red shading) and $\alpha$-Zr (blue shading) phases were 47.6% and 52.4%, respectively.