Equation of state of hydrous Fo_(90) ringwoodite to 45 GPa by synchroctron powder diffraction

摘要

The equation of state of Fo_(90) hydrous ringwoodite has been measured using X-ray powder diffraction to 45 GPa at the GSECARS beam line at the Advanced Photon Source synchrotron at Argonne National Laboratory. The sample was synthesized at 1400 deg C and 20 GPa in the 5000 ton multi anvil press at Bayerisches Geoinstitut in Bayreuth. The sample has the formula Mg_(1.70)Fe_(0.19)~(2+)Fe_(0.02)~(3+)H_(0.13)-Si_(1.00)O_4 as determined by electron microprobe, Fourier transform infrared and Mossbauer spectro-scopies, and contains approx 0.79 percent H_2O by weight. Compression of the sample had been been measured previously to 11 GPa by single crystal X-ray diffraction. A third-order Birch-Murnaghan equation of state fit to all of the data gives V_0 = 530.49 + - 0.07 A~3, K_0 = 174.6 + - 2.7 GPa and K' = 6.2 + - 0.6. The effect of 1 percent H incorporation in the structure on the bulk modulus is large and roughly equivalent to an increase in the temperature of approx 600 deg C at low pressure. The large value of K' indicates significant stiffening of the sample with pressure so that the effect of hydration decreases with pressure.