Quick Search:    advanced search

GSW Home   GeoRef Home   My GSW Alerts   Contact GSW   About GSW   Journals List   Help

This Article Figures Only Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in ISI Web of Science Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Allan, D.R. Articles by Pulham, C.R. Search for Related Content GeoRef GeoRef Citation

The high-pressure crystal structure of potassium hydrogen carbonate (KHCO₃)

¹ School of Chemistry and Centre for Science at Extreme Conditions, The University of Edinburgh, West Mains Road, Edinburgh, EH9 3JJ, U.K.
² ISIS Facility, CCLRC Rutherford Appleton Laboratory, Chilton, Didcot, OX11 0QX, U.K.

The crystal structure of the high-pressure phase of potassium hydrogen carbonate, here termed KHCO₃ form III, has been solved using single-crystal X-ray diffraction techniques. It adopts triclinic P symmetry and is formed on direct compression of the monoclinic ambient-pressure phase (kalicinite, form I) via a first-order phase transition at 3.2 GPa (V/V ~4%). We have also used time-of-flight high-pressure neutron powder-diffraction to determine the structural changes in KDCO₃ of the form I and III polymorphs to 8.3 GPa. This study indicates that the transition appears to be in response to pronounced displacements of the K⁺ cations and the cooperative tilting of the (DCO₃^–)₂ dimers. The O···O hydrogen bond distance shows a monotonic compression over the entire pressure range studied with no obvious discontinuity at the phase transition. However, the O-D···O bond angle appears to exhibit an abrupt ~4° decrease across the I–III phase transition with a concomitant change in its pressure dependence. Birch Murnaghan fits to the equation of state data above and below the transition indicate that form III [B₀ = 26.5(2.8) GPa, B' = 5.2(6)] is marginally less compressible than form I [B₀ = 22.7(8) GPa, B' = 4.1(5)].

Key Words: Kalicinite • high-pressure • crystal structure • phase transition