| Popis: |
The effects of compression on the structure and bonding of Mg(OH)2 brucite and Ca(OH)2 portlandite are documented to pressures of 34 and 24 GPa, respectively, by way of infrared spectroscopy of the O–H stretching vibration at 300 K. The frequency of the infrared‐active (A2u) mode of both hydroxides decreases with pressure, by −0.6 cm−1/GPa for Mg(OH)2 over the pressure range studied, and by −3.5 cm−1/GPa for Ca(OH)2 to 10.6 GPa. An additional mode observed in Mg(OH)2 is due to an optically induced hot band (A2u X A2u overtone): with increasing pressure, its intensity grows and its frequency decreases (−3.7 cm−1/GPa). The negative pressure dependencies of these modes (negative Gruneisen parameters) are explained in terms of compression increasing the hydrogen bond strength within the hydroxide structure. On increasing pressure above 12.8 GPa, the full width at half‐maximum of the O–H vibration in Ca(OH)2 rapidly broadens by a factor of 4. The infrared data suggest that Ca(OH)2 undergoes pressure‐induced am... |
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