Cation Exchange as a Route to Introduce Magnetism to Hybrid-Improper Polar Phases.

The pseudo Ruddlesden-Popper phase LiCaTaO is converted to ZnCaTaO, FeCaTaO, or CoCaTaO by reaction with the corresponding transition-metal dichloride. Diffraction data reveal that ZnCaTaO adopts a polar crystal structure (2) with the Zncations ordered into stripes within the interlayer coordination sites, and the TaO units adopt an /-() tilting pattern. In contrast, FeCaTaO and CoCaTaO adopt polar structures (2) with the transition-metal cations ordered in a checkerboard pattern within the interlayer coordination sites, and the TaO units adopt an / tilting pattern. The different polar structures adopted are rationalized on the basis of the size of the interlayer transition-metal cation. On cooling, FeCaTaO ( = 40 K) and CoCaTaO ( = 25 K) adopt antiferromagnetically ordered states with spins aligned parallel to the crystallographic stacking axis and arranged in a G-type manner. Close inspection of the NPD data collected from FeCaTaO at low temperature reveals a diffuse component to the magnetic scattering, which, in combination with magnetization data, suggest a glassy component to the low-temperature magnetic state. Neither FeCaTaO nor CoCaTaO shows significant lattice parameter anomalies around their respective Néel temperatures, in contrast to the previously reported manganese analogue MnCaTaO.