The natural occurrence of clinohumite in metabasalts and hydrothermally altered peridotites provides a source of water‐rich minerals in subducted slabs, making knowledge of their phase relations and crystal chemistry under high pressure‐temperature (P‐T) conditions important for understating volatile recycling and geodynamic process in the Earth's mantle. Here we present a synchrotron‐based, single‐crystal X‐ray diffraction study on two natural Ti‐bearing clinohumites up to ~28 GPa and 750 K in order to simulate conditions within subducted slabs. No phase transition occurs in clinohumite over this P‐T range. Pressure‐volume relationships of both compositions at room temperature were fitted to a third‐order Birch‐Murnaghan equation of state (EoS) with V₀ = 650.4(3) ų, K_T0 = 141(4) GPa, and K_T0′ = 4.0(6) for Ti‐poor clinohumite (0.07 Ti per formula unit, pfu) and V₀ = 650.8(3) ų, K_T0 = 144(4) GPa, and K_T0′ = 3.6(7) for Ti‐rich clinohumite (0.21 Ti pfu). Both clinohumites exhibit anisotropic compression with β_b > β_c > β_a. We also refined P‐V‐T equation of state parameters using the high‐temperature Birch‐Murnaghan EoS, yielding (∂K_T0/∂_T)_P = −0.040(10) GPa/K and α_T = 5.1(6) × 10⁻⁵ K⁻¹ for Ti‐poor clinohumite and (∂K_T0/∂_T)_P = −0.045(11) GPa/K and α_T = 5.7(6) × 10⁻⁵ K⁻¹ for Ti‐rich clinohumite. Ti‐poor and Ti‐rich clinohumites display similar equations of state but are ~20% more incompressible than Mg‐pure clinohumite and display ~5% higher bulk sound velocity than olivine at upper mantle conditions. Our results provide constraints for modeling geodynamic process related to the subduction and transport of potentially water‐rich slabs in the mantle.

High pressure–temperature experiments provide information on the phase diagrams and physical characteristics of matter at extreme conditions and offer a synthesis pathway for novel materials with useful properties. Experiments recreating the conditions of planetary interiors provide important constraints on the physical properties of constituent phases and are key to developing models of planetary processes and interpreting geophysical observations. The laser-heated diamond anvil cell (DAC) is currently the only technique capable of routinely accessing the Earth’s lower-mantle geotherm for experiments on non-metallic samples, but large temperature uncertainties and poor temperature stability limit the accuracy of measured data and prohibits analyses requiring long acquisition times. We have developed a novel internal resistive heating (IRH) technique for the DAC and demonstrate stable heating of non-metallic samples up to 3000 K and 64 GPa, as confirmed by in situ synchrotron x-ray diffraction and simultaneous spectroradiometric temperature measurement. The temperature generated in our IRH-DAC can be precisely controlled and is extremely stable, with less than 20 K variation over several hours without any user intervention, resulting in temperature uncertainties an order of magnitude smaller than those in typical laser-heating experiments. Our IRH-DAC design, with its simple geometry, provides a new and highly accessible tool for investigating materials at extreme conditions. It is well suited for the rapid collection of high-resolution P–V–T data, precise demarcation of phase boundaries, and experiments requiring long acquisition times at high temperature. Our IRH technique is ideally placed to exploit the move toward coherent nano-focused x-ray beams at next-generation synchrotron sources.

Lead phosphate Pb₃(PO₄)₂ was investigated by in situ synchrotron radiation X-ray diffraction and X-ray absorption near-edge structure (XANES) combined with diamond anvil cell technique up to 60.9 GPa. A pressure-induced phase transition of Pb₃(PO₄)₂ was observed from monoclinic (C2/c) to trigonal ( ) phases at about 1.7 GPa at room temperature. The high-pressure annealing experiment indicates that the trigonal phase of Pb₃(PO₄)₂ is stable at least up to 60.9 GPa. Isothermal pressure–volume relationship of trigonal Pb₃(PO₄)₂ is well described by the third-order Birch–Murnaghan equation of state with V₀ = 533(1) ų, K₀ = 89(4) GPa and K₀^′ = 5.8(2). In trigonal Pb₃(PO₄)₂, the a-axis is more compressible than the c-axis, showing an anisotropy elasticity. XANES results reveal the evolution of Pb local environment, i.e. the first-shell coordination number of Pb1 changes from 9 to 12 and the average Pb–O bond length increases at the crossover of C2/c-to- phase transition.

In the present study, we extensively explored the phase stabilities and elastic behaviors of Cu₂O with elevated pressures up to 29.3 GPa based on single-crystal X-ray diffraction measurements. The structural sequence of Cu₂O is different than previously determined. Specifically, we have established that Cu₂O under pressure, displays a cubic-tetragonal-monoclinic phase transition sequence, and a novel monoclinic high-pressure phase assigned to the P1a1 or P12/a1 space group was firstly observed. The monoclinic phase Cu₂O exhibits anisotropic compression with axial compressibility β_b > β_c > β_a in a ratio of 1.00:1.64:1.45. The obtained isothermal bulk modulus of cubic and monoclinic phase Cu₂O are 125(2) and 41(6) GPa, respectively, and the K_T0’ is fixed at 4. Our results provide new insights into the phase stability and elastic properties of copper oxides and chalcogenides at extreme conditions.

We present a synchrotron-based, single-crystal X-ray diffraction and Raman spectroscopy study of natural green dioptase (Cu ₆ Si ₆ O ₁₈ ·6H ₂ O) up to ∼30 GPa at room temperature. The lattice parameters of dioptase exhibit continuous compression behavior up to ∼14.5 GPa, whereupon a structural transition is observed. Pressure–volume data below 14.5 GPa were fitted to a second-order Birch–Murnaghan equation of state with V ₀ = 1440(2) Å ³ and K ₀ = 107(2) GPa, with K ₀ ′ = 4(fixed). The low-pressure form of dioptase exhibits anisotropic compression with axial compressibility β _a > β _c in a ratio of 1.14:1.00. Based on the diffraction data and Raman spectroscopy, the new high-pressure phase could be regarded as a dehydrated form of dioptase in the same symmetry group. Pressure-induced dehydration of dioptase contributes broadly to our understanding of the high-pressure crystal chemistry of hydrous silicates containing molecular water groups.

In the present study, we extensively explored the high-pressure behaviors and vibrational properties of amblygonite LiAlPO₄F with elevated pressures up to 34.3 GPa based on single-crystal X-ray diffraction measurements, Raman spectroscopy, and DFT calculations. The compressibility and elastic properties of amblygonite were determined first. Specifically, the obtained isothermal bulk modulus of LiAlPO₄F is 128(4) GPa and the triclinic phase exhibited anisotropic compression with axial compressibility β_c > β_a > β_b with a ratio of 1.11:1.00:1.20. The Raman spectra showed no indication of phase transformation and were used to obtained mode Grüneisen parameters. The average Grüneisen parameter for PO₄ tetrahedral sites was smaller than for the LiO₄F sites. Our results provide new insights into the phase stability and elastic properties of lithium-fluorite granites at extreme conditions.