Materials that take the perovskite structure have wide-reaching applications in many industries because of their varied properties that include magnetism, catalysis and ionic conduction. The basic perovskite structure takes the form ABX3, where A and B are positively charged and X represents the anion(s). The varied applications of the materials come from the fact that the structure is able to accommodate many different A and B cations, as well as a variety of anions.
As well as inorganic ions, it is also possible to introduce organic building blocks into the perovskite structure. Examples include the inclusion of HCO2- on the X site, in a series of phases studied for their ferroelectrics and multiferroics properties, and compounds based on organic cations, such as [(CH3)2NH2]PbI3, which are promising materials for next-generation solar cells.
Combining both of these, in this study, which featured on the cover of the European Journal of Inorganic Chemistry, the researchers made a series of lanthanide (Ln) containing compounds that included organic ions on both the A and X sites, with the composition ALn(HCO2)(C2O4)1.5.
This is the first time a perovskite made using a combination of inorganic and organic components has featured ordered anion vacancies combined with an A-site cation with a single charge and a triply charged B3+ ion. It was therefore important that the group were able to characterise the structure of the A cation.
This was challenging, as the disorder present on the A site meant that they were unable to determine the structure of the cation using crystallography. By using inelastic neutron scattering (INS) on the Tosca instrument at ISIS, in combination with infrared spectroscopy, they were able to confirm that the A cation in this series was, as planned, [(CH3)2NH2)]+.
This study shows the importance of the INS to this area of research, as the technique is highly sensitive to the bonds between hydrogen and other atoms, which are a key part of the organic components of these materials.
Lead researcher, Paul Saines from the University of Kent explains; “INS offers potential use in a much wider range of perovskites with organic components to confirm their composition, since A-cation disordered is very common in these materials, and thereby the ability to optimise these for applications."
The full paper can be found online at DOI: 10.1002/ejic.202100591