Summary: | A structure and equation of the state of δ-AlOOH has been studied at room temperature, up to 29.35 GPa, by means of single crystal X-ray diffraction in a diamond anvil cell using synchrotron radiation. Above ~10 GPa, we observed a phase transition with symmetry changes from <inline-formula><math display="inline"><semantics><mrow><mi>P</mi><msub><mn>2</mn><mn>1</mn></msub><mi>n</mi><mi>m</mi></mrow></semantics></math></inline-formula> to <inline-formula><math display="inline"><semantics><mrow><mi>P</mi><mi>n</mi><mi>n</mi><mi>m</mi></mrow></semantics></math></inline-formula>. Pressure-volume data were fitted with the second order Birch-Murnaghan equation of state and showed that, at the phase transition, the bulk modulus (K<sub>0</sub>) of the calculated wrt 0 pressure increases from 142(5) to 216(5) GPa.
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