Self-Assembled Surfactant-Polyoxovanadate Soft Materials as Tuneable Vanadium Oxide Cathode Precursors for Lithium-Ion Batteries.

The mixing of [V10 O28 ]6- decavanadate anions with a dicationic gemini surfactant (gem) leads to the spontaneous self-assembly of surfactant-templated nanostructured arrays of decavanadate clusters. Calcination of the material under air yields highly crystalline, sponge-like V2 O5 (gem-V2 O5 ). In contrast, calcination of the amorphous tetrabutylammonium decavanadate allows isolation of a more agglomerated V2 O5 consisting of very small crystallites (TBA-V2 O5 ). Electrochemical analysis of the materials' performance as lithium-ion intercalation electrodes highlights the role of morphology in cathode performance. The large crystallites and long-range microstructure of the gem-V2 O5 cathode deliver higher initial capacity and superior capacity retention than TBA-V2 O5 . The smaller crystallite size and higher surface area of TBA-V2 O5 allow faster lithium insertion and superior rate performance to gem-V2 O5 .

Non-collinear magnetism in the post-perovskite thiocyanate frameworks CsM(NCS)3.

AMX3 compounds are structurally diverse, a notable example being the post-perovskite structure which adopts a two-dimensional framework with corner- and edge-sharing octahedra. Few molecular post-perovskites are known and of these, none have reported magnetic structures. Here we report the synthesis, structure and magnetic properties of molecular post-perovskites: CsNi(NCS)3, a thiocyanate framework, and two new isostructural analogues CsCo(NCS)3 and CsMn(NCS)3. Magnetisation measurements show that all three compounds undergo magnetic order. CsNi(NCS)3 (Curie temperature, T C = 8.5(1) K) and CsCo(NCS)3 (T C = 6.7(1) K) order as weak ferromagnets. On the other hand, CsMn(NCS)3 orders as an antiferromagnet (Néel temperature, T N = 16.8(8) K). Neutron diffraction data of CsNi(NCS)3 and CsMn(NCS)3, show that both are non-collinear magnets. These results suggest molecular frameworks are fruitful ground for realising the spin textures required for the next generation of information technology.

Controlling multiple orderings in metal thiocyanate molecular perovskites A x {Ni[Bi(SCN)6]}.

We report four new A-site vacancy ordered thiocyanate double double perovskites, , A = K+, NH4 +, CH3(NH3)+ (MeNH3 +) and C(NH2)3 + (Gua+), including the first examples of thiocyanate perovskites containing organic A-site cations. We show, using a combination of X-ray and neutron diffraction, that the structure of these frameworks depends on the A-site cation, and that these frameworks possess complex vacancy-ordering patterns and cooperative octahedral tilts distinctly different from atomic perovskites. Density functional theory calculations uncover the energetic origin of these complex orders and allow us to propose a simple rule to predict favoured A-site cation orderings for a given tilt sequence. We use these insights, in combination with symmetry mode analyses, to show that these complex orders suggest a new route to non-centrosymmetric perovskites, and mean this family of materials could contain excellent candidates for piezo- and ferroelectric applications.