Neutron Diffraction Study of the Structure of Paraelectric Phase of Pb₅Ge₃O₁₁

Abstract

The structure of paraelectric phase of Pb 5 Ge 3 O 11 was refined by the least squares calculations of single crystal neutron diffraction data at 200°C. Final R value was 0.08 and the type of phase transition was determined as displacive one. The existence of unstable oxygen atom which is lying on the mirror plane perpendicular to the c -axis was found to have relation with the reorientation of GeO 4 group. Atomic displacements through the phase transition were evaluated and used for the calculation of the spontaneous polarization for the point charge model. This gave P s to be 2.0 µC/cm 2 , a smaller value than the observed one of 4.2 µC/cm 2 at room temperature.