Neutron diffraction study of the structure of paraelectric phase of Pb5Ge3O11

The structure of paraelectric phase of Pb5Ge3O11 was refined by the least squares calculations of single crystal neutron diffraction data at 2000C. 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 GeO4 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 sub(s) to be 2.0 μC/cm2, a smaller value than the observed one of 4.2 μC/cm2 at room temperature. (auth.)