Structure relations in the family of the solid solution HfxZr1–xO2

Melanie Nentwich1
1Melanie Nentwich, Melanie.Nentwich@desy.de, Deutsches Elektronen-Synchrotron DESY, Notkestraße 85, 22607 Hamburg, Germany

Fig. 1: df

Hafnium Zirconium Oxide HfxZr1–xO2 is a potentially ferroelectric material with great perspectives in semiconductor applications, due to its compatibility with silicon technologies and its low toxicity. Despite its chemical simplicity, the solid solution HfxZr1–xO2 comprises a large variety of different phases. We compiled a complete list of experimentally and theoretically reported HfxZr1–xO2 structures. All of them are symmetrically related to the common aristotype with Fluorite type structure. The summetry relationships between those structures have been determined and are presented in a Bärnighausen-like tree [1]. Interestingly, not all symmetry reductions follow the conventional group-subgroup relations and involve severe atomic shifts. Further, the structures were compared to each other in detail regarding the dimensionality of atomic shifts and the accompanied lattice distortions. In total, nine of the 23 structure types have a polar space group allowing for ferroelectricity; six of them still lack for experimental evidence. Finally, the information provided by the Bärnighausen-like tree was used to transform the indices of a reflection before and after a phase transition. This conversion allows the study of (dis)appearing reflections during phase transitions. 
[1] H Bärnighausen Group-subgroup relations between space groups: a useful tool in crystal chemistry” MATCH, 9, 139 (1980)

M. N. acknowledges financial support through CREMLINplus, which received funding by European Union’s HORIZON 2020 research and innovation programme under grant agreement No., 871072.