Sound velocities of Al‐bearing phase D were investigated up to 22 GPa and 1300 K using in situ synchrotron X‐ray techniques combined with ultrasonic measurements in a multianvil apparatus. The isothermal bulk modulus of Al‐bearing phase D was found to be ~16.7% lower than that of Mg‐endmember, suggesting a strong effect of Al incorporation on the bulk modulus of phase D. Al‐bearing phase D has higher P‐ (V_P) and S‐ (V_S) wave velocities compared to other mantle transition zone minerals, up to 4.3% for V_P and up to 9.6% for V_S compared with hydrous iron‐bearing ringwoodite, which might engender reduction of velocity contrast between anhydrous mantle and hydrous slab components. The accumulation of hydrated slab components carrying Al‐phase D in the uppermost lower mantle can explain some local negative shear velocity perturbations (ΔV_S) up to −1.5%, although ΔV_P (−0.5%) is expected to remain below the detection limit of seismological techniques.

The structure of hydrous amorphous SiO₂ is fundamental in order to investigate the effects of water on the physicochemical properties of oxide glasses and magma. The hydrous SiO₂ glass with 13 wt.% D₂O was synthesized under high-pressure and high-temperature conditions and its structure was investigated by small angle X-ray scattering, X-ray diffraction, and neutron diffraction experiments at pressures of up to 10 GPa and room temperature. This hydrous glass is separated into two phases: a major phase rich in SiO₂ and a minor phase rich in D₂O molecules distributed as small domains with dimensions of less than 100 Å. Medium-range order of the hydrous glass shrinks compared to the anhydrous SiO₂ glass by disruption of SiO₄ linkage due to the formation of Si–OD deuterioxyl, while the response of its structure to pressure is almost the same as that of the anhydrous SiO₂ glass. Most of D₂O molecules are in the small domains and hardly penetrate into the void space in the ring consisting of SiO₄ tetrahedra.

In order to make high-speed deposition of diamond effective, diamond growth rates for gas-phase microwave plasma chemical vapor deposition and in-liquid microwave plasma chemical vapor deposition are compared. A mixed gas of methane and hydrogen is used as the source gas for the gas-phase deposition, and a methanol solution of ethanol is used as the source liquid for the in-liquid deposition. The experimental system pressure is in the range of 60–150 kPa. While the growth rate of diamond increases as the pressure increases, the amount of input microwave energy per unit volume of diamond is $1\text{kW}\text{h}/{\text{mm}}^3$ regardless of the method used. Since the in-liquid deposition method provides a superior cooling effect through the evaporation of the liquid itself, a higher electric input power can be applied to the electrodes under higher pressure environments. The growth rate of in-liquid microwave plasma chemical vapor deposition process is found to be greater than conventional gas-phase microwave plasma chemical vapor deposition process under the same pressure conditions.