High-pressure Brillouin scattering of $\text{Pb}\left({\text{Mg}}_{1/3}{\text{Nb}}_{2/3}\right){\text{O}}_3$

The pressure dependencies of the elastic constants and bulk modulus of single crystal $\text{Pb}\left({\text{Mg}}_{1/3}{\text{Nb}}_{2/3}\right){\text{O}}_3$ (PMN) have been measured up to 10 GPa at room temperature by Brillouin spectroscopy. The elastic moduli and elastic anisotropy undergo an abrupt change at 4.5 GPa, indicative of a phase transition and consistent with earlier Raman and x-ray diffraction studies. We suggest that PMN undergoes a structural change from a cubic $Pm3m$ to rhombohedral $R3c$ phase at 4.5 GPa.

Figure 1

(Color online) A typical set of Brillouin spectra at selected angles at 7.6 GPa. The longitudinal $\left(L\right)$ and transverse (T) modes are clearly visible.

Figure 2

(Color online) Plot of the experimental (marks) and model (lines) Brillouin shifts (GHz) of the longitudinal and transverse modes with angle for the $a\text{−}b$ plane of the PMN crystal at 1.4 GPa.

Figure 3

(Color online) Pressure dependencies of the second-order elastic moduli. The marks are experimental data and dashed lines are guides to the eye. The inset shows the pressure dependencies of the bulk and shear moduli. The shear modulus was given as the Voigt-Reuss-Hills average.

Figure 4

(Color online) Pressure dependence of the elastic anisotropy of PMN. The marks are the data and the dashed line is a guide to the eye. It is obvious that there is an abrupt change in the elastic anisotropy of PMN at 4.5 GPa.