The first observation of a pressure-induced phase transition and compression behavior of kalicinite (KHCO3) at room temperature

In situ synchrotron X-ray diffraction measurements were performed on kalicinite (KHCO3) up to 9.0 GPa at room temperature. A reversible phase transition was observed at about 2.8 GPa. The structure of the high-pressure phase has not been identified yet. The compression behavior of kalicinite is highly anisotropic and the a-axis is about two times more compressible than the b- and c-axes. The compression behavior is different from that during contraction in lowering the temperature and this suggests that the hydrogen bonded O⋯O distance is significantly shortened with increasing pressure.