An infrared spectroscopic study of the OH stretching frequencies of talc and 10-A phase to 10 GPa

The effects of pressure on the OH stretching frequencies of natural talc and two samples of synthetic 10-angstrom phase have been measured using a diamond-anvil cell and a synchrotron infrared source. The 10-A phase was synthesized at 6.0-6.5 GPa, 600 degrees C for 46 hours (sample 10 angstrom-46) and 160 hours (10 angstrom-160). Spectra were collected up to 9.0 GPa (talc), 9.9 GPa (10 angstrom-46), and 9.6 GPa (10 angstrom-160). The OH stretching vibration of Mg3OH groups in talc occurs at 3677 cm(-1) at ambient pressure, and increases linearly with pressure at 0.97(2) cm(-1) GPa(-1). The same vibration occurs in 10-angstrom phase, but shows negligible pressure shift up to 2 GPa, above which the frequency increases linearly to the maximum pressure studied, at a rate of 0.96(3) cm(-1) GPa(-1) (10 angstrom-46) and 0.87(3) cm(-1) GPa(-1) (10 angstrom-160). Two other prominent bands in the 10-angstrom phase spectrum are suggested to be due to stretching of interlayer H2O, hydrogen-bonded to the nearest tetrahedral sheet. These bands also show little change over the first 2 GPa of compression, as most of the compression of the structure is taken up by closing non-hydrogen bonded gaps between interlayer H2O and tetrahedral sheets. Between 2 and 4 GPa, changes in band intensities suggest a rearrangement of the interlayer H2O.