The reaction of the lacunary polyoxometalate precursor Na[B-α-BiWO]·19.5HO with Cu(II) ions was explored in search of new economic ways to copper tungstobismuthates as interesting prototypes for water oxidation and reduction catalysts. The emerging series of new 0D-3D polyoxometalate architectures with distinct copper cores was structurally characterized. NaRb[Cu(HO)(BiWO)] (Cu-4) and 3D-KCuH[(CuCl)(KCu(HO))(B-α-BiWO)]·13HO (Cu-5) display a Cu(HO) core. The 2D representatives Na[Cu(HO)Cl(BiWO)] (Cu-1a), Na[Cu(HO)(BiWO)] (Cu-1b), 2D-NaKCuCl[Cu(HO)(BiWO)] (Cu-2), and 2D-NaKCu[Cu(HO)(BiWO)] (Cu-3) contain Cu(HO)WO cores. Interestingly, the bismuth-free 1D paratungstate B NaKCu[HWO] (Cu-6) is formed through reassembly of the precursor. Cu-5 displays a disordered transition metal core, implying the presence of the polyanions [Cu(HO)(BiWO)] and [Cu(HO)(BiWO)]. The magnetic properties of Cu-5 as well as its activity as visible-light-driven H and O evolution catalyst were evaluated.

The development of economic water oxidation catalysts is a key step toward large-scale water splitting. However, their current exploration remains empirical to a large extent. Elucidating the correlations between electronic properties and catalytic activity is crucial for deriving general and straightforward catalyst design principles. Herein, strongly correlated electronic systems with abundant and easily tunable electronic properties, namely La(1-x)Sr(x)BO3 perovskites and La(2-x)Sr(x)BO4 layered perovskites (B = Fe, Co, Ni, or Mn), were employed as model systems to identify favorable electronic structures for water oxidation. We established a direct correlation between the enhancement of catalytic activity and the insulator to metal transition through tuning the electronic properties of the target perovskite families via the La(3+)/Sr(2+) ratio. Their improved photochemical water oxidation performance was clearly linked to the increasingly metallic character. These electronic structure-activity relations provide a promising guideline for constructing efficient water oxidation catalysts.

Solid solutions of the magnetic insulators Ba

We discuss an experiment in which two magnetic insulators that both show a field-induced magnetic-ordering transition are weakly coupled to one another and are placed into an ex- ternal magnetic field. If the respective magnetic states can be interpreted as phase coherent Bose-Einstein condensates of magnetic bosonic quasiparticles, one expects the occurrence of Josephson effects. For two identical systems, the resulting d.c. Josephson effect formally represents a constant quasiparticle Josephson current across the weak link, which turns out to be unobservable in an experiment. For magnetic insulators with different critical fields, a spontaneous alternating quasiparticle current develops with a leading oscillation frequency {\omega}a.c. that is determined by the difference between the critical fields. As a result of the coupling, additional sidebands appear in the energy spectrum of the coupled device that would be absent without phase coherence. We discuss the primary conditions for such an effect to take place and conclude that its detection can be feasible for a proper choice of compounds with suitable and realistic material parameters.Comment: This version has been adapted to Elsevier style. The interpretation of the d.c. Josephson effect is more explicit. The role of the phase of the triplon-BEC-wavefunction is precisely defined to address a possible ambiguity with respect to the in-plane angle of the transverse magnetic moments. We include a remark in the conclusion on the possibility of an intrinsic Josephson effect in BaCuCi2O

The spin dimer system Ba 3−x Sr x Cr 2 O 8 is a solid solution of the triplon Bose-Einstein condensation candidates Ba 3 Cr 2 O 8 and Sr 3 Cr 2 O 8. The magnetic intradimer interaction constant J 0 in this spin system can be tuned by varying the Sr content x. Very interestingly, this variation of J 0 with x is highly nonlinear. In the present study, we show that this peculiar behavior of J 0 can be only partly explained by the changes in the average crystal structure alone. We report on neutron powder diffraction experiments to probe the corresponding structural details. Performing extended Hückel tight-binding calculations based on those structural details obtained at liquid-helium temperatures, we found that the change of the magnetic interaction constant can be well reproduced by taking into account the presence of a structural transition due to the Jahn-Teller active Cr 5+ ions. This transition, lifting the orbital degeneracy and thereby the magnetic frustration in the system, is heavily influenced by disorder in the system arising from partially exchanging Ba with Sr.