In-situ observation of pressure-induced symmetrization of hydrogen bond in -AlOOH and HD isotope effect

Sano, Asami   ; Hattori, Takanori   

-AlOOH is a distorted rutile type hydrous phase. X-ray study have found the change in compressibility at high-pressure, with an isotope effect on the transition pressure. To examine the pressure response of hydrogen bond in -AlOOH and its DH isotope difference, we performed neutron diffraction experiments at high-pressure neutron diffractometer PLANET in MLF, J-PARC. The transition from P21nm to Pnnm, which can be attributed to the disorder of hydrogen bond or the symmtrization was found at 12.1 GPa for -AlOOD, at the same pressure where the change in compressibility was reported. The significant shortening of O...O distance and hydrogen bond was observed to 12.1 GPa; however, the O...O distance remains almost constant above the transition pressure. This study reveals that slight change of hydrogen position can induce the increase of bulk modulus in -AlOOH at high pressure.