First-Principles Study of Structure and Magnetism in Copper(II)-Containing Hybrid Perovskites

We report a first-principles study of hybrid organic–inorganic perovskites with formula [A]Cu(H2POO)3 (A = triazolium (Trz) and guanidinium (Gua), and H2POO− = hypophosphite), and [HIm]Cu(HCO2)3 (HIm = imidazolium cation, HCO2− = formate). The triazolium hypophosphite and the formate have been suggested as possible ferroelectrics. We study the fully relaxed structures with different magnetic orderings and possible phonon instabilities. For the [Trz]Cu hypophosphite, the Trz cation is shown to induce large octahedral distortions due to the Jahn-Teller effect, with Cu-O long-bond ordering along two perpendicular directions, which is correlated with antiferromagnetic ordering and strongly one-dimensional. We find that the structure is dynamically stable with respect to zone-center distortions, but instabilities appear along high symmetry lines in the Brillouin zone. On the other hand, for the [HIm]Cu formate, large octahedral distortions are found, with large Cu-O bonds present in half of the octahedra, in this case along a single direction, and correspondingly, the magnetism is almost two-dimensional.