Hybrid Improper Ferroelectricity in (Sr,Ca)SnO and Beyond: Universal Relationship between Ferroelectric Transition Temperature and Tolerance Factor in n = 2 Ruddlesden-Popper Phases.

Hybrid improper ferroelectricity, which utilizes nonpolar but ubiquitous rotational/tilting distortions to create polarization, offers an attractive route to the discovery of new ferroelectric and multiferroic materials because its activity derives from geometric rather than electronic origins. Design approaches blending group theory and first principles can be utilized to explore the crystal symmetries of ferroelectric ground states, but in general, they do not make accurate predictions for some important parameters of ferroelectrics, such as Curie temperature ( T). Here, we establish a predictive and quantitative relationship between T and the Goldschmidt tolerance factor, t, by employing n = 2 Ruddlesden-Popper (RP) ABO as a prototypical example of hybrid improper ferroelectrics.

Spatio-temporal symmetry - crystallographic point groups with time translations and time inversion.

The crystallographic symmetry of time-periodic phenomena has been extended to include time inversion. The properties of such spatio-temporal crystallographic point groups with time translations and time inversion are derived and one representative group from each of the 343 types has been tabulated. In addition, stereographic symmetry and general-position diagrams are given for each representative group.

Magnetostriction-polarization coupling in multiferroic MnMnWO.

Double corundum-related polar magnets are promising materials for multiferroic and magnetoelectric applications in spintronics. However, their design and synthesis is a challenge, and magnetoelectric coupling has only been observed in NiTeO among the known double corundum compounds to date. Here we address the high-pressure synthesis of a new polar and antiferromagnetic corundum derivative MnMnWO, which adopts the NiTeO-type structure with low temperature first-order field-induced metamagnetic phase transitions (T  = 58 K) and high spontaneous polarization (~ 63.

A(II)GeTeO (A = Mn, Cd, Pb): Non-Centrosymmetric Layered Tellurates with PbSbO-Related Structure.

A(II)GeTeO (A = Mn, Cd, Pb), new non-centrosymmetric (NCS) honeycomb-layered tellurates, were synthesized and characterized. A(II)GeTeO (A = Mn, Cd, Pb) crystallize in trigonal space group P312 (No. 149) of edge-sharing GeO and TeO octahedra, which form honeycomb-like-layers in the ab-plane with A(II) (A = Mn, Cd, Pb) cations located between the layers.