High-pressure properties of diaspore,AlO(OH) |
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Authors: | A Friedrich D J Wilson E Haussühl B Winkler W Morgenroth K Refson V Milman |
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Institution: | 1.Institut für Geowissenschaften, Abt. Kristallographie,Johann Wolfgang Goethe-Universit?t Frankfurt,Frankfurt am Main,Germany;2.Insitut für Anorganische Chemie,Georg August Universit?t,G?ttingen,Germany;3.Department of Chemistry,Aarhus University,Aarhus C,Denmark;4.c/o DESY/HASYLAB,Hamburg,Germany;5.Rutherford Appleton Laboratory, Chilton, Didcot,Oxfordshire,UK;6.Accelrys Inc., 334 Cambridge Science Park,Cambridge,UK |
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Abstract: | The structural compression mechanism and compressibility of diaspore, AlO(OH), were investigated by in situ single-crystal
synchrotron X-ray diffraction at pressures up to 7 GPa using the diamond-anvil cell technique. Complementary density functional
theory based model calculations at pressures up to 40 GPa revealed additional information on the pressure-dependence of the
hydrogen-bond geometry and the vibrational properties of diaspore. A fit of a second-order Birch–Murnaghan equation of state
to the p–V data resulted in the bulk modulus B
0 = 150(3) GPa and B
0 = 150.9(4) GPa for the experimental and theoretical data, respectively, while a fit of a third-order Birch–Murnaghan equation
of state resulted in B
0 = 143.7(9) GPa with its pressure derivative B′ = 4.4(6) for the theoretical data. The compression is anisotropic, with the a-axis being most compressible. The compression of the crystal structure proceeds mainly by bond shortening, and particularly
by compression of the hydrogen bond, which crosses the channels of the crystal structure in the (001) plane, in a direction
nearly parallel to the a-axis, and hence is responsible for the pronounced compression of this axis. While the hydrogen bond strength increases with
pressure, a symmetrisation is not reached in the investigated pressure range up to 40 GPa and does not seem likely to occur
in diaspore even at higher pressures. The stretching frequencies of the O–H bond decrease approximately linearly with increasing
pressure, and therefore also with increasing O–H bond length and decreasing hydrogen bond length.
Electronic Supplementary Material The online version of this article () contains supplementary material, which is available to authorized users. |
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Keywords: | Diaspore High pressure Crystal structure Synchrotron radiation Density functional theory calculations |
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