Single-crystal Brillouin spectroscopy with CO2 laser heating and variable q

Single-Crystal Elasticity of α-Hydroquinone-An Analogue for Organic Planetary Materials

In this study, we measured the single-crystal elasticity of α-hydroquinone at ambient conditions using Brillouin spectroscopy to assess the feasibility of this technique for studying the mechanical properties of organic ices in the outer solar system. In this study, α-hydroquinone serves as an ambient temperature analogue for low-temperature organic ices on Titan and other solar system bodies. We found that a satisfactory Brillouin spectrum can be obtained in less than 5 min of experimental time with negligible damage to the sample. The best fit single-crystal elastic moduli of α-hydroquinone were determined as C 11 = 13.67(8) GPa, C 33 = 10.08(6) GPa, C 44 = 4.54(5) GPa, C 12 = 6.9(7) GPa, C 13 = 7.02(7) GPa, C 14 = 0.54(4) GPa, C 25 = 0.51(9) GPa, and C 66 = (C 11 - C 12)/2 = 3.4(3) GPa, with bulk modulus K S = 8.7(2) GPa and shear modulus G = 3.4(3) GPa. These results demonstrate that Brillouin spectroscopy is a powerful tool for characterizing the elastic properties of organic materials. The elastic properties of organic ices can be broadly applied to understand planetary surface processes and also aid in evaluating the feasibility and technical readiness of future lander, sampling, and rover missions in the outer solar system.

Constraining composition and temperature variations in the mantle transition zone

The mantle transition zone connects two major layers of Earth’s interior that may be compositionally distinct: the upper mantle and the lower mantle. Wadsleyite is a major mineral in the upper mantle transition zone. Here, we measure the single-crystal elastic properties of hydrous Fe-bearing wadsleyite at high pressure-temperature conditions by Brillouin spectroscopy. Our results are then used to model the global distribution of wadsleyite proportion, temperature, and water content in the upper mantle transition zone by integrating mineral physics data with global seismic observations. Our models show that the upper mantle transition zone near subducted slabs is relatively cold, enriched in wadsleyite, and slightly more hydrated compared to regions where plumes are expected. This study provides direct evidence for the thermochemical heterogeneities in the upper mantle transition zone which is important for understanding the material exchange processes between the upper and lower mantle.

A new study by @JinZhang_MP models the global distribution of wadsleyite proportion, temperature and water content in the upper mantle transition zone.

Grain size dependent high-pressure elastic properties of ultrafine micro/nanocrystalline grossular

We have performed sound velocity and unit cell volume measurements of three synthetic, ultrafine micro/nanocrystalline grossular samples up to 50 GPa using Brillouin spectroscopy and synchrotron X-ray diffraction. The samples are characterized by average grain sizes of 90 nm, 93 nm and 179 nm (hereinafter referred to as samples Gr90, Gr93, and Gr179, respectively). The experimentally determined sound velocities and elastic properties of Gr179 sample are comparable with previous measurements, but slightly higher than those of Gr90 and Gr93 under ambient conditions. However, the differences diminish with increasing pressure, and the velocity crossover eventually takes place at approximately 20-30 GPa. The X-ray diffraction peaks of the ultrafine micro/nanocrystalline grossular samples significantly broaden between 15-40 GPa, especially for Gr179. The velocity or elasticity crossover observed at pressures over 30 GPa might be explained by different grain size reduction and/or inhomogeneous strain within the individual grains for the three grossular samples, which is supported by both the pressure-induced peak broadening observed in the X-ray diffraction experiments and transmission electron microscopy observations. The elastic behavior of ultrafine micro/nanocrystalline silicates, in this case, grossular, is both grain size and pressure dependent.

A Review of the Melting Curves of Transition Metals at High Pressures Using Static Compression Techniques

The accurate determination of melting curves for transition metals is an intense topic within high pressure research, both because of the technical challenges included as well as the controversial data obtained from various experiments. This review presents the main static techniques that are used for melting studies, with a strong focus on the diamond anvil cell; it also explores the state of the art of melting detection methods and analyzes the major reasons for discrepancies in the determination of the melting curves of transition metals. The physics of the melting transition is also discussed.

A Practical Review of the Laser-Heated Diamond Anvil Cell for University Laboratories and Synchrotron Applications

In the past couple of decades, the laser-heated diamond anvil cell (combined with in situ techniques) has become an extensively used tool for studying pressure-temperature-induced evolution of various physical (and chemical) properties of materials. In this review, the general challenges associated with the use of the laser-heated diamond anvil cells are discussed together with the recent progress in the use of this tool combined with synchrotron X-ray diffraction and absorption spectroscopy.

A CO2 laser heating system for in situ high pressure-temperature experiments at HPCAT

We present a CO₂ laser heating setup for synchrotron x-ray diffraction inside a diamond anvil cell, situated at HPCAT (Sector 16, Advanced Photon Source, Argonne National Lab, Illinois, USA), which is modular and portable between the HPCAT experiment hutches. The system allows direct laser heating of wide bandgap insulating materials to thousands of degrees at static high pressures up to the Mbar regime. Alignment of the focused CO₂ laser spot is performed using a mid-infrared microscope, which addressed past difficulties with aligning the invisible radiation. The implementation of the mid-infrared microscope alongside a mirror pinhole spatial filter system allows precise alignment of the heating laser spot and optical pyrometry measurement location to the x-ray probe. A comparatively large heating spot (∼50 μm) relative to the x-ray beam (<10 μm) reduces the risk of temperature gradients across the probed area. Each component of the heating system and its diagnostics have been designed with portability in mind and compatibility with the various experimental hutches at the HPCAT beamlines. We present measurements on ZrO₂ at 5.5 GPa which demonstrate the improved room-temperature diffraction data quality afforded by annealing with the CO₂ laser. We also present in situ measurements at 5.5 GPa up to 2800 K in which we do not observe the postulated fluorite ZrO₂ structure, in agreement with recent findings.