Many material properties such as superconductivity, magnetoresistance or magnetoelectricity emerge from the non-linear interactions of spins and lattice/phonons. Hence, an in-depth understanding of spin–phonon coupling is at the heart of these properties. While most examples deal with one magnetic lattice only, the simultaneous presence of multiple magnetic orderings yield potentially unknown properties. We demonstrate a strong spin–phonon coupling in SmFeO3 that emerges from the interaction of both, iron and samarium spins. We probe this coupling as a remarkably large shift of phonon frequencies and the appearance of new phonons. The spin–phonon coupling is absent for the magnetic ordering of iron alone but emerges with the additional ordering of the samarium spins. Intriguingly, this ordering is not spontaneous but induced by the iron magnetism. Our findings show an emergent phenomenon from the non-linear interaction by multiple orders, which do not need to occur spontaneously. This allows for a conceptually different approach in the search for yet unknown properties.
A new metastable phase in flash-frozen disordered Prussian blue analogues is reported. The phase is characterised by the appearance of diffuse scattering clouds and the reduction of the local structure symmetry: from cubic to a tetragonal or lower space group. The phase transition is characterised by the translational modulation of the structure and is likely caused by the freezing of the water confined in the pores of the structure.
Prussian Blue Analogues (PBAs) are transition metal cyanides, widely investigated due to their catalytic and optical activity, ability to transport and store ions and small gas molecules. The later property is allowed by the presence of the large number of structural hexacyanometallate vacancies, which connect to form a porous network. These vacancies are filled with water: coordinated water molecules, which replace missing cyanide groups, and zeolitic water in the spherical cavities.In this work we report a novel diffuse scattering signal, appearing after fast freezing of the PBA crystals. This signal emerges in the form of diffuse "clouds" around the Bragg peaks, which grow in intensity at higher Q, and are caused by the corrugation of the atomic lattice. We hypothesize that this corrugation is the response of the PBA lattice to the stress developed by water freezing in the nanopores. Furthermore, we discuss the effect of freezing on mechanical properties of Mn[Co] PBA.
Disorder is commonly used in chemistry for designing functional materials. For instance, preparation of solid solutions is nothing else than the introduction of a controlled number of point defects in a crystal. Disordered systems, though, provide more degrees of freedom: not only the number of defects, but also their distribution can be used to optimise the functional properties of materials, however up until now, defect distribution was hard to control and thus was rarely used in practice.In this talk we will show how to precisely tune distribution of point defects by changing various chemical parameters during crystal growth and characterise it with the single crystal diffuse scattering [1].We will use Prussian Blue Analogues (PBAs) as our model system. PBAs is a class of cyanide materials with the general formula M[M'(CN) 6] 1-δ * xH2O where M and M' are transition metals.Depending on the nature of transition metals, PBAs can accommodate a large number of vacancies on the M'(CN) 6 site (for instance δ=0.33 for M=Mn and M'=Co) which makes them highly porous and, as a result, attractive for hydrogen storage applications. Distribution of M'(CN) 6 vacancies is important for the performance of this material, since more disordered vacancy configurations provide more diffusion pathways through the structure, larger accessible volume, and easier transport.
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