High pressure synthesis of orthorhombic SnO2

A dense form of SnO₂ with an orthorhombic structure has been synthesized at 158 kbar and 800 °C. The boundary separating the normal pressure phase (tetragonal SnO₂-I) from the high pressure phase (orthorhombic SnO₂-II) is represented by P(kbar) = 140.0 + 0.022 T(°C). The lattice parameters of the quenched high pressure phase (SnO₂-II) are : $\text{a}\text{= 4.714 ± 0.001}\text{A}\text{?}$, $\text{b}\text{= 5.727 ± 0.001}\text{A}\text{?}$ and $\text{c}\text{= 5.214 ± 0.001}\text{A}\text{?}$ with the cell volume $\text{V}\text{= 140.8 ± 0.1}\text{A}\text{?}{}^3$. The volume decrease for the transition is calculated to be 1.8 %.