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1. A diamond anvil microassembly for Joule heating and electrical measurements up to 150 GPa and 4000 K

   https://doi.org/10.1063/5.0184911  

   Geballe, Zachary_M; Vitale, Suzy_M; Yang, Jing; Miozzi, Francesca; Dobrosavljevic, Vasilije_V; Walter, Michael_J (March 2024, Journal of Applied Physics)

   When diamond anvil cell (DAC) sample chambers are outfitted with both thermal insulation and electrodes, two cutting-edge experimental methods are enabled: Joule heating with spectroradiometric temperature measurement and electrical resistance measurements of samples heated to thousands of kelvin. The accuracy of temperature and resistance measurements, however, often suffers from poor control of the shape and location of the sample, electrodes, and thermal insulation. Here, we present a recipe for the reproducible and precise fabrication of DAC sample, electrodes, and thermal insulation using a three-layer microassembly. The microassembly contains two potassium chloride thermal insulation layers, four electrical leads, a sample, and a buttressing layer made of polycrystalline alumina. The sample, innermost electrodes, and buttress layer are fabricated by focused-ion-beam milling. Three iron samples are presented as proof of concept. Each is successfully compressed and pulsed Joule heated while maintaining a four-point probe configuration. The highest pressure-temperature condition achieved is ∼150 GPa and 4000 K. 

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2. Dynamic compression effects of ${\mathrm{H}}_2\mathrm{O}$ in a dynamic diamond anvil cell: Origin of metastable ice VII and its crystal growth kinetics

   https://doi.org/10.1103/PhysRevB.111.104105  

   Howard, Alex; Kim, Minseob; Smith, Jesse; Yoo, Choong-Shik (March 2025, Physical Review B)

   We report on the structural verification of metastable ice VII solidifying in the phase space of ice VI at 1.80 GPa at room temperature. Using time-resolved (TR) x-ray diffraction and TR ruby luminescence paired with high-speed microphotography utilizing a dynamic diamond anvil cell, an initial compression rate range from 0.12 to 95.84 GPa/s was explored. The solidification pressure of metastable ice VII has a potential sigmoidal dependence upon compression rate with a turnover compression rate of ∼80 GPa/s. The preferred crystallization of ice VII in the stability field of ice VI is due to the increased nucleation rate of ice VII over ice VI at 1.77 GPa that is driven by the surface energy difference between the liquid and solid phases along with the change in Gibbs free energy of solidification. The dynamic pressure-volume–compression behaviors of ice phases (VI and VII) show a lattice stiffening in both phases, especially during the compression loading. It is also found that the compression rate greatly affects the solid-solid phase transition between ice VI and VII but does not affect the liquid-solid transition between water and ice VI as much. Lastly, a third phase transition was found to occur after metastable ice VII transforms into high-density amorphous (HDA) ice, which could be a disordered hydrogen-bonded network configuration of ice VII forming out of HDA ice facilitated by the decoupling of the oxygen movement and reorientation of the ${\mathrm{H}}_2\mathrm{O}$molecule. These results demonstrate the complexity of a seemingly simple molecule ${\mathrm{H}}_2\mathrm{O}$, how it can readily change its static properties with the modification of (de)compression rate, and highlight the need to use multiple TR structural and spectroscopic probes at higher time resolutions to realize the most comprehensive understanding. 

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3. Carbide Formation in Refractory Mo15Nb20Re15Ta30W20 Alloy under a Combined High-Pressure and High-Temperature Condition

   https://doi.org/10.3390/e22070718  

   Zhang, Congyan; Bhandari, Uttam; Zeng, Congyuan; Ding, Huan; Guo, Shengmin; Yan, Jinyuan; Yang, Shizhong (July 2020, Entropy)

   null (Ed.)

   In this work, the formation of carbide with the concertation of carbon at 0.1 at.% in refractory high-entropy alloy (RHEA) Mo15Nb20Re15Ta30W20 was studied under both ambient and high-pressure high-temperature conditions. The x-ray diffraction of dilute carbon (C)-doped RHEA under ambient pressure showed that the phases and lattice constant of RHEA were not influenced by the addition of 0.1 at.% C. In contrast, C-doped RHEA showed unexpected phase formation and transformation under combined high-pressure and high-temperature conditions by resistively employing the heated diamond anvil cell (DAC) technique. The new FCC_L12 phase appeared at 6 GPa and 809 °C and preserved the ambient temperature and pressure. High-pressure and high-temperature promoted the formation of carbides Ta3C and Nb3C, which are stable and may further improve the mechanical performance of the dilute C-doped alloy Mo15Nb20Re15Ta30W20. 

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4. Multiple freezing–melting pathways of high-density ice through ice XXI phase at room temperature

   https://doi.org/10.1038/s41563-025-02364-x  

   Lee, Yun-Hee; Kim, Jin Kyun; Kim, Yong-Jae; Kim, Minju; Cho, Yong Chan; Husband, Rachel J; Strohm, Cornelius; Ehrenreich-Petersen, Emma; Glazyrin, Konstantin; Laurus, Torsten; et al (October 2025, Nature Materials)

   Abstract Various metastable ice phases and their complicated transition pathways have been found by pressurization at low temperatures at which slow kinetics and high metastability are easily achieved. By contrast, such diversity is less expected at room or elevated temperatures. Here, using a combination of a dynamic diamond anvil cell and X-ray free electron laser techniques, we demonstrate that supercompressed water transforms into ice VI through multiple freezing–melting pathways at room temperature, hidden within the pressure region of ice VI. These multiple transition pathways occur via a metastable ice (more specifically, ice XXI with body-centred tetragonal structure ($$I\bar{4}2d$$ $I\overline{4}2d$)) discovered in this study and a metastable ice VII that exists within the pressure range of ice VI. We find that supercompressed water structurally evolves from high-density water to very-high-density water, causing multiple transition pathways. These findings provide an insight to find more metastable ice phases and their transition pathways at elevated temperatures. 

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5. Thermoelastic Properties of Eclogitic Garnets and Omphacites: Implications for Deep Subduction of Oceanic Crust and Density Anomalies in the Upper Mantle

   https://doi.org/10.1029/2018GL081170  

   Xu, Jingui; Zhang, Dongzhou; Fan, Dawei; Dera, Przemyslaw K.; Shi, Feng; Zhou, Wenge (January 2019, Geophysical Research Letters)

   Abstract Synchrotron‐based high‐pressure/high‐temperature single‐crystal X‐ray diffraction experiments to ~24 GPa and 700 K were conducted on eclogitic garnets (low‐Fe: Prp₂₈Alm₃₈Grs₃₃Sps₁and high‐Fe: Prp₁₄Alm₆₂Grs₁₉Adr₃Sps₂) and omphacites (low‐Fe: Quad₅₇Jd₄₂Ae₁and high‐Fe: Quad₅₃Jd₂₇Ae₂₀), using an externally heated diamond anvil cell. Fitting the pressure‐volume‐temperature data to a third‐order Birch‐Murnaghan equation of state yields the thermoelastic parameters including bulk modulus (K_T0), its pressure derivative (K′_T0), temperature derivative ((∂K_T/∂T)_P), and thermal expansion coefficient (α_T). The densities of the high‐Fe and low‐Fe eclogites were then modeled along typical geotherms of the normal mantle and the subducted oceanic crust to the transition zone depth (550 km). The metastable low‐Fe eclogite could be a reason for the stagnant slabs within the upper range of the transition zone. Eclogite would be responsible for density anomalies within 100–200 km in the upper mantle of Asia. 

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