Incommensurate crystal structure of PbHfO3

Controversy in the description/identification of so-called intermediate phase(s) in PbHfO 3 , stable in the range ∼420–480 K, has existed for a few decades. A synchrotron diffraction experiment on a partially detwinned crystal allowed the structure to be solved in the superspace group Imma (00γ) s 00 (No. 74.2). In contrast to some previously published reports, in the pure compound only one distinct phase was observed between Pbam PbZrO 3 -like antiferroelectric and Pm 3 m paraelectric phases. The modulation vector depends only slightly on temperature. The major structure modulation is associated with the displacement of lead ions, which is accompanied by a smaller amplitude modulation for the surrounding O atoms and tilting of HfO 6 octahedra. Tilting of the octahedra results in a doubling of the unit cell compared with the parent structure.