Analysis of Structures and Order Parameters in Antiferroelectric PbHfO3 Using Neutron Diffraction

We performed structural analysis of PbHfO 3 between 10 and 500 K in the room-temperature antiferroelectric phase and the cubic phase using powder neutron diffraction. Disordered arrangements of Pb atoms were not detected in the cubic phase in contrast to the results of X-ray diffraction. This indicates that Pb atoms have an electron-density distribution that spreads out more widely than the expected distribution in isolated Pb ions. The simple concept of order parameters in soft-mode condensation, that is, all atomic shifts show proportional temperature dependences, was not observed in the antiferroelectric phase of PbHfO 3 . However, physical properties, such as lattice distortion, show the temperature dependences predicted on the basis of a phenomenological theory as if the simple concept were applicable over the entire temperature range.