Low-Temperature Structure of PbTiO3

Abstract

Measurements of the perturbed $\ensuremath{\gamma}\ensuremath{-}\ensuremath{\gamma}$ directional correlation have been made for the first excited state of $^{44}\mathrm{Sc}$ in polycrystalline lead titanate at -(189\ifmmode\pm\else\textpm\fi{}5) \ifmmode^\circ\else\textdegree\fi{}C. A static electric quadrupole interaction was observed, having an interaction strength $|Q{V}_{\mathrm{zz}}|=(4.09\ifmmode\pm\else\textpm\fi{}0.09)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}8}$ V, which is greater than the value obtained at room temperature by a factor of 1.04\ifmmode\pm\else\textpm\fi{}0.02. The field gradient at the $^{44}\mathrm{Sc}$-ion site is found to have axial symmetry, indicating a tetragonal structure for lead titanate at -189\ifmmode^\circ\else\textdegree\fi{}C. The axial ratio at this temperature is estimated to be 1.108\ifmmode\pm\else\textpm\fi{}0.027, which agrees well with recent x-ray studies indicating a new tetragonal phase formed by a transition at -160\ifmmode^\circ\else\textdegree\fi{}C. Using a recently reported value of ${\ensuremath{\gamma}}_{\ensuremath{\infty}} ({\mathrm{Sc}}^{3+})$, the quadrupole moment of the 68-keV state in $^{44}\mathrm{Sc}$ is found to be (0.109\ifmmode\pm\else\textpm\fi{}0.020) b. Using this number it is shown that the room-temperature values of field gradient observed with $^{44}\mathrm{Sc}$ and $^{57}\mathrm{Fe}$ probes differ by a factor of 16.5.