Neutron scattering study at high pressure of the structural phase transition in paratellurite

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Abstract
The dispersion relation for the transverse acoustic phonon mode propagating along (110) polarized along (110) in TeO2 has been measured at P=1 atm, Pc( approximately=9.0 kbar), and 2Pc where Pc is the tetragonal-to-orthorhombic structural transition pressure. Complete softening of the mode at Pc is restricted to the q to 0 limit while at finite wavevectors there is a nearly constant energy shift of the dispersion curve of approximately=-0.1 meV between 1 atm and Pc and approximately=+0.25 meV between Pc and 2Pc. Measurements of the order parameter are consistent with a mean field of a pressure-induced elastic instability.