High-pressure Raman scattering and luminescence studies of ${\mathrm{Bi}}_2\mathrm{W}{\mathrm{O}}_6:{\mathrm{Eu}}^{3+}$, which is a member of the bismuth layered Aurivillius family of ferroelectrics, are presented. These studies showed the onset of two reversible second order phase transitions near 3.4 and $6.2\mathrm{GPa}$. The pressure dependence of Raman bands provides strong evidence that the first phase transition involves the loss of the $\mathrm{W}{\mathrm{O}}_6$ tilt mode around the pseudotetragonal axis. This structural change may be the same as that observed at ambient pressure at $660°\mathrm{C}$ (from the $Pca{2}_1$ to $B2cb$ structure). The second phase transition is associated with the instability of a low wave number mode, which behaves as soft mode. The discovery of the soft mode in ${\mathrm{Bi}}_2\mathrm{W}{\mathrm{O}}_6$ that corresponds most likely to the $E_u$ mode responsible for ferroelectricity in Aurivillius family of compounds proves that this transition is of displacive type. Our studies also suggest that the structure above $6.2\mathrm{GPa}$ is orthorhombic and centrosymmetric and, consequently, the phase transition can be classified as a pressure-induced ferroelectric to a paraelectric phase transition.

• Received 7 January 2008

DOI:https://doi.org/10.1103/PhysRevB.77.094137