Natural smithsonite (ZnCO₃) has been investigated by synchrotron radiation X-ray diffraction and X-ray absorption spectroscopy combined with diamond anvil cells up to 50 GPa at room temperature. At ambient pressure, smithsonite adopts as calcite phase with a=4.6557(11) Å and c=15.072(12) Å. Both experimental results demonstrate that no phase transition occurs in the present examined pressure range. Isothermal pressure–volume relationship of smithsonite can be well described by the third-order Birch–Murnaghan equation of state with V₀=284.6(7) ų, B₀=126.8(6) GPa and (fixed). The axial compressibility of smithsonite presents clear anisotropy with α_c=3.60×10⁻³ Å GPa⁻¹>α_a=1.21×10⁻³Å GPa ⁻¹. ZnCO₃-smithsonite is proposed to approach the NaCl rocksalt structure on compression.

An investigation into the high-pressure behavior of AX(2)-type iron pnictides was conducted using first-principles calculations based on density functional theory within the generalized gradient approximation. Our results demonstrate that a phase transition from the marcasite to the CuAl(2) occurs at 108 GPa for FeP(2), at 92 GPa for FeAs(2), and at 38 GPa for FeSb(2), accompanying a semiconductor-to-metal crossover. A linear relationship between bulk moduli and the inverse specific volume is proposed to be B(0) = 17 498/V(0)-45.9 GPa for the marcasite-type phase and B(0) = 31 798/V(0)-67.5 GPa for the CuAl(2)-type phase. According to the observed structural evolutions, we claim that the regular marcasite transforms to the CuAl(2)-type phase and the anomalous marcasite transforms to the pyrite-type phase at high pressures.

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.