As a major branch of hybrid perovskites, two-dimensional (2D) hybrid double perovskites are expected to be ideal systems for exploring novel ferroelectric properties, because they can accommodate a variety of organic cations and allow diverse combinations of different metal elements. However, no 2D hybrid double perovskite ferroelectric has been reported since the discovery of halide double perovskites in the 1930s. Based on trivalent rare-earth ions and chiral organic cations, we have designed a new family of 2D rare-earth double perovskite ferroelectrics, A4MIMIII(NO3)8, where A is the organic cation, MI is the alkaline metal or ammonium ion, and MIII is the rare-earth ion. This is the first time that ferroelectricity is realized in 2D hybrid double perovskite systems. These ferroelectrics have achieved high-temperature ferroelectricity and photoluminescent properties. By varying the rare-earth ion, variable photoluminescent properties can be achieved. The results reveal that the 2D rare-earth double perovskite systems provide a promising platform for achieving multifunctional ferroelectricity.

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Substitution of A‐site and/or X‐site ions of ABX3‐type perovskites with organic groups can give rise to hybrid perovskites, many of which display intriguing properties beyond their parent compounds. However, this method cannot be extended effectively to hybrid antiperovskites. Now, the design of hybrid antiperovskites under the guidance of the concept of Goldschmidt's tolerance factor is presented. Spherical anions were chosen for the A and B sites and spherical organic cations for the X site, and seven hybrid antiperovskites were obtained, including (F3(H2O)x)(AlF6)(H2dabco)3, ((Co(CN)6)(H2O)5)(MF6)(H2dabco)3 (M=Al3+, Cr3+, or In3+), (Co(CN)6)(MF6)(H2pip)3 (M=Al3+ or Cr3+), and (SbI6)(AlF6)(H2dabco)3. These new structures reveal that all ions at A, B, and X sites of inorganic antiperovskites can be replaced by molecular ions to form hybrid antiperovskites. This work will lead to the synthesis of a large family of hybrid antiperovskites.

The (H2dabco)[Na(BF4)3] undergoes a static-to-dynamic phase transition at 403/386 K. Crystal structure analysis reveals that H2dabco2+ and/or BF4− undergo disordering.

A layered hybrid rare-earth double perovskite-type molecule-based compound (3HQ)4[RbEu(NO3)8] (3HQ = 3-Quinuclidinone cation, 1) was synthesized. It undergoes a reversible phase transition and switchable dielectric constant behavior above room temperature...