Equation of state and phase transition in KAlSi3O8 hollandite at high pressure

NEW PUBLICATION IN AMERICAN MINERALOGIST

The tetragonal hollandite structure (KAlSi3O8 hollandite) has been studied up to 32 GPa at room temperature using high-pressure in-situ X-ray diffraction techniques. A phase transformation from tetragonal I4/m phase to a new phase was found to occur at about 20 GPa. This transition is reversible on release of pressure without noticeable hysteresis and hence this new high-pressure phase is unquenchable to ambient conditions. The volume change associated with the transition is found to be small (not measurable), suggesting a second order transition. The diffraction pattern of the high-pressure phase can be indexed in a monoclinic unit cell (space group I2/m), which is isostructual with BaMn8O16 hollandite. The  » angle of the monoclinic unit cell increases continuously above the transition. A Birch-Murnaghan equation of state Þ t to pressure-volume data obtained for KAlSi3O8 hollandite yields a bulk modulus K0 = 201.4 (7) GPa with K’0 = 4.0.


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