Three series of conjugated microporous polymers (CMPs) were studied as photocatalysts for hydrogen production from water using a sacrificial hole scavenger. In all cases, dibenzo[b,d]thiophene sulfone polymers outperformed their fluorene analogues. A porous network, S-CMP3, showed the highest hydrogen evolution rates of 6076 μmol h −1 g −1 (λ > 295 nm) and 3106 μmol h −1 g −1 (λ > 420 nm), with an external quantum efficiency of 13.2% at 420 nm. S-CMP3 outperforms its linear structural analogue, P35, whereas in other cases, nonporous linear polymers are superior to equivalent porous networks. This suggests that microporosity might be beneficial for sacrificial photocatalytic hydrogen evolution, if suitable linkers are used that do not limit charge transport and the material can be wetted by water as studied here by water sorption and quasi-elastic neutron scattering.

The antiferromagnetic structures of the layered oxychalcogenides (Sr(1-x)Ba(x))(2)CoO(2)Cu(2)S(2) (0 ≤ x ≤ 1) have been determined by powder neutron diffraction. In these compounds Co(2+) is coordinated by four oxide ions in a square plane and two sulfide ions at the apexes of an extremely tetragonally elongated octahedron; the polyhedra share oxide vertexes. The magnetic reflections present in the diffraction patterns can in all cases be indexed using a √2a × √2a × c expansion of the nuclear cell, and nearest-neighbor Co(2+) moments couple antiferromagnetically within the CoO(2) planes. The ordered magnetic moment of Co(2+) in Sr(2)CoO(2)Cu(2)S(2) (x = 0) is 3.8(1) μ(B) at 5 K, consistent with high-spin Co(2+) ions carrying three unpaired electrons and with an additional significant unquenched orbital component. Exposure of this compound to moist air is shown to result in copper deficiency and a decrease in the size of the ordered moment to about 2.5 μ(B); there is a strong correlation between the size of the long-range ordered moment and the occupancy of the Cu site. Both the tetragonal elongation of the CoO(4)S(2) polyhedron and the ordered moment in (Sr(1-x)Ba(x))(2)CoO(2)Cu(2)S(2) increase with increasing Ba content, and in Ba(2)CoO(2)Cu(2)S(2), which has Co(2+) in an environment that is close to purely square planar, the ordered moment of 4.5(1) μ(B) at 5 K is over 0.7 μ(B) larger than that in Sr(2)CoO(2)Cu(2)S(2), so the unquenched orbital component in this case is even larger than that observed in octahedral Co(2+) systems such as CoO. The experimental observations of antiferromagnetic ground states and the changes in properties resulting from replacement of Sr by Ba are supported by ab initio calculations on Sr(2)CoO(2)Cu(2)S(2) and Ba(2)CoO(2)Cu(2)S(2). The large orbital moments in these systems apparently result from spin-orbit mixing of the unequally populated d(xz), d(yz), and d(z(2)) orbitals, which are reckoned to be almost degenerate when the CoO(4)S(2) polyhedron reaches its maximum elongation. The magnitudes of the ordered moments in high-spin Co(2+) oxide, oxychalcogenide, and oxyhalide systems are shown to correlate well with the tetragonal elongation of the coordination environment. The large orbital moments lead to an apparently magnetostrictive distortion of the crystal structures below the Neél temperature, with the symmetry lowered from tetragonal I4/mmm to orthorhombic Immm and the size of the distortion correlating well with the size of the long-range ordered moment for all compositions and for temperature-dependent data gathered on Ba(2)CoO(2)Cu(2)S(2).

We have performed extensive ab initio calculations to investigate phonon dynamics and their possible role in superconductivity in BaFe2As2 and related systems. The calculations are compared to inelastic neutron scattering data that offer improved resolution over published data [Mittal et al., PRB 78 104514 (2008)], in particular at low frequencies. Effects of structural phase transition and full/partial structural relaxation, with and without magnetic ordering, on the calculated vibrational density of states are reported. Phonons are best reproduced using either the relaxed magnetic structures or the experimental cell. Several phonon branches are affected by the subtle structural changes associated with the transition from the tetragonal to the orthorhombic phase. Effects of phonon induced distortions on the electronic and spin structure have been investigated. It is found that for some vibrational modes, there is a significant change of the electronic distribution and spin populations around the Fermi level. A peak at 20 meV in the experimental data falls into the pseudo-gap region of the calculation. This was also the case reported in our recent work combined with an empirical parametric calculation [Mittal et al., PRB 78 104514 (2008)]. The combined evidence for the coupling of electronic and spin degrees of freedom with phonons is relevant to the current interest in superconductivity in BaFe2As2 and related systems.

A quantum magnet, LiCuSbO 4 , with chains of edge-sharing spin-½ CuO 6 octahedra is reported. While short-range order is observed for T < 10 K, no zero-field phase transition or spin freezing occurs down to 100 mK. Specific heat indicates a distinct high field phase near the 12 T saturation field. Neutron scattering shows incommensurate spin correlations with q = (0.47±0.01)π/a and places an upper limit of 70 µeV on any spin gap. Exact diagonalization of 16-spin easy-plane spin-½ chains with competing ferro-and antiferromagnetic interactions (J 1 = -75 K, J 2 = 34 K) accounts for the T > 2 K data. PACS: 75.10.Jm, 75.30.Kz, 75.40.Cx, 75.30.Et 2 The Heisenberg spin-½ chain is one of very few quantum critical systems to be realized in a crystalline solid. An element of frustration is added by next-nearest-neighbor (NNN) interactions (J 2 ). [1][2][3] In such systems, theoretical work [4][5][6][7][8][9] indicates that qualitatively different quantum phases are possible as a function of α = J 2 /J 1 , axial exchange anisotropy, ∆, and the applied field h = gµ B H/|J 1 |. Finite values of α are observed in copper oxide spin-chains formed by corner-or edge-sharing Jahn-Teller distorted CuO 6 polyhedra. [10][11][12][13][14][15][16][17] While the sign and magnitude of J 1 is dependent on the α c ) from a short-range ordered (SRO) phase with a small yet finite gap (α < α c ). 20Dimer, spiral, vector-chiral and multipolar phases have been predicted as a function of α, ∆ and h. 4,6,8 Interest has been further amplified by the observation that ferroelectricity accompanies magnetic ordering in some of these systems. 14,21,22 Known spin-½ FM-AFM chains span a wide range of α and include Li 2 CuO 2 , 17,21,22 Here we present the structure and magnetic properties of the one-dimensional (1D) spin chain compound LiCuSbO 4 . Due to weak inter-chain interactions it has no 3D ordering down to 100 mK and can be driven to a saturated-FM phase above the experimentally accessible field <µ o H s > = 12 T. The magnetic susceptibility, isothermal magnetization and specific heat can be simultaneously modelled for T > 2 K using the approximate spin Hamiltonian:Here θ is the angle between the applied field, h, and the unique molecular axis, z. The parameters J 1 = -75K, α = -0.45, and ∆ = 0.83 account for the main features in the thermomagnetic data and are also consistent with the magnetic excitations measured by inelastic neutron scattering.Powder samples of LiCuSbO 4 were prepared using a ceramic synthesis. 25LiCuSbO 4 has an orthorhombic structure 26, 27 related to that of LiFeSnO 4 . 28Rietveld analysis 29 of powder neutron diffraction data acquired on the BT1 diffractometer at NIST 30 was carried out using FULLPROF. 31The final fit, with the corr...

). We have measured the temperature dependence of phonon spectra in these compounds and analyzed them using ab-initio calculations. The spectra of the two compounds show large differences that cannot be explained by simple mass renormalization of the modes involving Zn (65.38 amu) and Ni (58.69 amu) atoms. This reflects the fact that the structure and bonding are quite different in the two compounds. The calculated pressure dependence of the phonon modes and of the thermal expansion coefficient, α V , are used to understand the anomalous behavior in these compounds. Our ab-initio calculations indicate that it is the low-energy rotational modes in Zn(CN) 2 , which are shifted to higher energies in Ni(CN) 2 , that are responsible for the large negative thermal expansion. The measured temperature dependence of the phonon spectra has been used to estimate the total anharmonicity of both compounds. For Zn(CN) 2 , the temperature-dependent measurements (total anharmonicity), along with our previously reported pressure dependence of the phonon spectra (quasiharmonic), is used to separate the explicit temperature effect at constant volume (intrinsic anharmonicity).

Fast-ion conductors are critical to the development of solid-state batteries. The effects of mechanochemical synthesis that lead to increased ionic conductivity in an archetypical sodium-ion conductor Na 3 PS 4 are not fully understood. We present here a comprehensive analysis based on diffraction (Bragg, pair distribution function), spectroscopy (impedance, Raman, NMR, INS) and ab-initio simulations aimed at elucidating the synthesis-property relationships in Na 3 PS 4. We consolidate previously reported interpretations about the local structure of ball-milled samples, underlining the sodium disorder and showing that a local tetragonal framework more accurately describes the structure than the originally proposed cubic one. Through variable-pressure impedance spectroscopy measurements, we report for the first time the activation volume for Na + migration in Na 3 PS 4 , which is ~30% higher for the ball-milled samples. Moreover, we show that the effect of ball-milling on increasing the ionic conductivity of Na 3 PS 4 to ~10-4 S/cm can be reproduced by applying external pressure on a sample from conventional high temperature ceramic synthesis. We conclude that the key effects of mechanochemical synthesis on the properties of solid electrolytes can be analyzed and understood in terms of pressure, strain and activation volume. File list (2) download file view on ChemRxiv Na3PS4_mechanical_v10.1.pdf (2.18 MiB) download file view on ChemRxiv SI_Na3PS4_mechanical_v10.1.pdf (2.38 MiB)

Ligand field splitting energies of lanthanides Ln 3+ (Ln = from Ce to Yb) in octahedral environment are calculated using the Hohenberg-Kohn theorems based orbital-free embedding formalism. The lanthanide cation is described at orbital level whereas its environment is represented by means of an additional term in the Kohn-Sham-like one-electron equations expressed as an explicit functional of two electron densities: that of the cation and that of the ligands. The calculated splitting energies, which are in good agreement with the ones derived from experiment, are attributed to two main factors: (i) polarization of the electron density of the ligands, and; (ii) ion-ligand Pauli repulsion.

Recently colossal positive volume thermal expansion has been found in the framework compounds Ag 3 Co(CN) 6 and Ag 3 Fe(CN) 6 . Phonon spectra have been measured using the inelastic neutron scattering technique as a function of temperature and pressure. The data has been analyzed using ab-initio calculations. We find that the bonding is very similar in both compounds. At ambient pressure modes in the intermediate frequency part of the vibrational spectra in the Co compound are shifted to slightly higher energies as compared to the Fe compound. The temperature dependence of the phonon spectra gives evidence for large explicit anharmonic contribution to the total anharmonicity for low-energy modes below 5 meV. We found that modes are mainly affected by the change in the size of unit cell, which in turn changes the bond lengths and vibrational frequencies. Thermal expansion has been calculated via the volume dependence of phonon spectra. Our analysis indicates that Ag phonon modes in the energy range from 2 to 5 meV are strongly anharmonic and major contributors to thermal expansion in both compounds. The application of pressure hardens the low-energy part of the phonon spectra involving Ag vibrations and confirms the highly anharmonic nature of these modes.