Synthesis, structure, and single-crystal elasticity of Al-bearing superhydrous phase B

Abstract Dense hydrous magnesium silicates (DHMSs) with large water contents and wide stability fields are a potential H2O reservoir in the deep Earth. Al-bearing superhydrous phase B (shy-B) wider field than Al-free counterpart can play an important role understanding transport Earth’s transition zone topmost lower mantle. In this study, nominally two different shy-B samples 0.47(2) 1.35(4) Al atoms per formula unit (pfu), were synthesized using rotating multi-anvil press. Their single-crystal structures investigated by X-ray diffraction (XRD) complemented Raman spectroscopy Fourier-transform infrared (FTIR). Single-crystal XRD shows that cell parameters decrease increasing Al-content. By combining results, we conclude Al-poor crystallizes Pnn2 space group hydrogen general positions. Based on results of refinements combined FTIR spectroscopy, three substitutions mechanisms proposed: 2Al3+ = Mg2+ + Si4+; ☐Mg2+ 2H+ (☐Mg2+ means vacancy Mg site); Si4+ Al3+ H+. Thus, addition to H positions, is incorporated into mineral via point defects. The elastic stiffness coefficients measured for Al-shy-B 1.35 pfu Brillouin scattering (BS). C11, higher C22, similar C33 when compared shy-B. anisotropy also composition. Such properties due effect lattice contraction as whole specific chemical substitution mechanism affect bonds strength. velocity, anisotropy, thermodynamic help understand low-velocity high-anisotropy region subducted slab located Tonga.