Abstract
X-ray diffraction of SnO2 cassiterite at high pressures and temperatures demonstrates the existence of four phase transitions to 117 GPa. The observed sequence of phases for SnO2 is rutile-type P42 /mnm → CaCl2-typePnnm → pyrite-typePa3 → ZrO2 orthorhombic phase I Pbca → cotunnite-type Pnam. Our observations of the first three phases are generally in agreement with earlier studies. The orthorhombic phase I and cotunnite-type structure orthorhombic phase II were observed in SnO2 for the first time. The Pbca phase is found at 50–74 GPa during room-temperature compression. The cotunnite-type structure was synthesized when SnO2 was compressed to 74 GPa and heated at 1200 K. The cotunnite-type form was observed during compression between 54–117 GPa with additional laser heating carried out at 91 and 111 GPa. Fitting the pressure-volume data for the high-pressure phases to the second-order Birch-Murnaghan equation of state yields a bulk modulus of 25926 GPa for the Pbca phase and 4177 GPa for the cotunnite-type phase.
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