Edmund J. Cussen

Twelve-connected porous metal–organic frameworks with high H2 adsorption

The twelve-connected metal-organic frameworks {[Ni(3)(OH)(L)(3)].n(solv)}(infinity) and {[Fe(3)(O)(L)(3)].n(solv)}(infinity) [LH(2) = pyridine-3,5-bis(phenyl-4-carboxylic acid)] have been prepared and characterised: these materials can be desolvated to form porous materials that show adsorption of H(2) up to 4.15 wt% at 77 K.

The structure of lithium garnets: cation disorder and clustering in a new family of fast Li+ conductors

The structure of the fast lithium-ion conducting garnets Li5La3M2O12 (M = Ta, Nb) reveals Li+ on both tetrahedral and octahedral sites and suggests that the latter are responsible for the observed Li+ mobility via a clustering mechanism.

Structure and ionic conductivity in lithium garnets

Garnets are capable of accommodating an excess of lithium cations beyond that normally found in this prototypical structure. This excess lithium is found in a mixture of coordination environments with considerable positional and occupational disorder and leads to ionic conductivity of up to 4 × 10−4 S cm−1 at room temperature. This high value for total conductivity, combined with excellent thermal and (electro)chemical resistance makes these candidate materials for operation in all solid-state batteries. This review looks at garnets with a wide range of stoichiometries and lithium concentrations and the impact of complex lithium distributions and crystallographic order/disorder transitions on the transport properties of these materials.

Neutron diffraction study of the influence of structural disorderon the magnetic properties of Sr2FeMO6 (M=Ta,Sb)

The crystal structure of the perovskite Sr 2 FeTaO 6 has been refined by simultaneous analysis of X-ray and neutron powder diffraction data collected at 280 K; space group Pbnm, a=5.6204(3), b=5.6161(3), c=7.9266(3) A. The structure is of the GdFeO 3 type, with a disordered distribution of Fe and Ta over the six-coordinate cation sites. The structure of Sr 2 FeSbO 6 has been refined in a similar manner; space group P2 1 /n, a=5.6132(5), b=5.5973(5), c=7.9036(7) A, β=90.01(1)°. The two crystallographically distinct six-coordinate sites in Sr 2 FeSbO 6 are occupied in a partially ordered manner [0.795(6):0.205(6)] by Fe and Sb atoms. Neutron diffraction data collected from Sr 2 FeTaO 6 at 1.5 K show no evidence of long-range magnetic ordering and, in the light of previous susceptibility and Mossbauer measurements, it is concluded that Sr 2 FeTaO 6 is a spin glass below 23 K. Neutron diffraction data collected from Sr 2 FeSbO 6 at 1.5 K include magnetic Bragg peaks characteristic of a type I magnetic structure with an average ordered moment of 3.06(9) µ B per Fe atom on the Fe-dominated octahedral site, and no significant ordered moment on the second site. The magnetic Bragg scattering decreases to zero in the temperature interval 1.5≤T/K≤37(2). It is concluded that the partial cation ordering leads to the coexistence of a magnetically ordered spin system and a spin-glass system.

Low-temperature densification of Al-doped Li7La3Zr2O12: a reliable and controllable synthesis of fast-ion conducting garnets

The application of Li7La3Zr2O12 as a Li+ solid electrolyte is hampered by the lack of a reliable procedure to obtain and densify the fast-ion conducting cubic garnet polymorph. Dense cubic Li7La3Zr2O12-type phases are typically formed as a result of Al-incorporation in an unreliable reaction with the alumina crucible at elevated temperatures of up to 1230 °C. High Al3+-incorporation levels are also believed to hinder the three-dimensional movement of Li+ in these materials. Here, a new, facile hybrid sol–gel solid-state approach has been developed in order to accomplish reliable and controllable synthesis of these phases with low Al-incorporation levels. In this procedure, sol–gel processed solid precursors of Li7La3Zr2O12 and Al2O3 nanosheets are simply mixed using a pestle and mortar and allowed to react at 1100 °C for 3 h to produce dense cubic phases. Fast-ion conducting Al-doped Li7La3Zr2O12 phases with the lowest reported Al3+-content (∼0.12 mol per formula unit), total conductivities of ∼3 × 10−4 S cm−1, bulk conductivities up to 0.6 mS and ion conduction activation energies as low as 0.27 eV, have been successfully achieved. The ease of lithium diffusion in these materials is attributed to the formation of dense cubic phases with low Al3+ dopant ratios. This approach is applicable to Li7−xLa3Zr2−xTaxO12 phases and opens up a new synthetic avenue to Li7La3Zr2O12-type materials with greater control over resulting characteristics for energy storage applications.

Fast microwave-assisted synthesis of Li-stuffed garnets and insights into Li diffusion from muon spin spectroscopy

Lithium-stuffed garnets attract huge attention due to their outstanding potential as solid-state electrolytes for lithium batteries. However, there exists a persistent challenge in the reliable synthesis of these complex functional oxides together with a lack of complete understanding of the lithium-ion diffusion mechanisms in these important materials. Addressing these issues is critical to realizing the application of garnet materials as electrolytes in all solid-state lithium-ion batteries. In this work, a cubic phase garnet of nominal composition Li6.5Al0.25La2.92Zr2O12 is synthesized through a microwave-assisted solid-state route for the first time, reducing considerably the reaction times and heating temperatures. Lithium-ion diffusion behavior is investigated by electrochemical impedance spectroscopy (EIS) and state-of-art muon spin relaxation (μSR) spectroscopy, displaying activation energies of 0.55 ± 0.03 eV and 0.19 ± 0.01 eV respectively. This difference arises from the high inter-grain resistance, which contributes to the total resistance in EIS measurements. In contrast, μSR acts as a local probe providing insights on the order of the lattice, giving an estimated value of 4.62 × 10−11 cm2 s−1 for the lithium diffusion coefficient. These results demonstrate the potential of this lithium-stuffed garnet as a solid-state electrolyte for all-solid state lithium-ion batteries, an area of growing interest in the energy storage community.

Incommensurate phases in the Ba-Mn-Pd-O system

Polycrystalline samples of bulk composition Ba 5 Mn 3 PdO 12 , Ba 6 Mn 4 PdO 15 , and Ba 7 Mn 5 PdO 18 have been synthesised and characterised by X-ray diffraction, electron diffraction and magnetometry. These compounds adopt a 2H-related crystal structure consisting of [001] chains of MnO 6 and PdO 6 polyhedra, with Ba 2+ cations separating the chains. The three compounds, each of which is commensurate in the xy plane but incommensurate along the z axis, differ in the ratio of octahedra to trigonal prisms in the chains (3:1, 4:1 and 5:1 respectively). The lattice parameters of the four dimensional trigonal unit cell are typically a≈10.02 A, c 1 ≈4.3 A, c 2 ≈2.61 A. The homogeneity and crystallinity of the samples increases with the ratio of octahedra to trigonal prisms and is greater in the xy plane than parallel to z. The magnetic susceptibility of all three phases deviates from the Curie-Weiss law below 100 K, but no magnetic phase transition is apparent above 5 K.

Structural and magnetic properties of Ba2LuMoO6: a valence bond glass

We report here the synthesis of the site ordered double perovskite Ba(2)LuMoO(6). Rietveld refinement of room temperature powder x-ray diffraction measurements indicates that it crystallizes in the cubic space group Fm3m, with a = 8.3265(1) Å. Powder neutron diffraction data indicate that, unusually, this cubic symmetry is maintained down to 2 K, with [Formula: see text], Mo(5+) ions situated on the frustrated face-centred cubic lattice. Despite dc-susceptibility measurements showing Curie-Weiss behaviour with strong antiferromagnetic interactions at T ≥ 200 K, there is no evidence of long range magnetic ordering at 2 K. At T ≤ 50 K, susceptibility measurements indicate a loss in moment to ∼18% of the expected value, and there is a corresponding loss in the magnitude of the magnetic exchange. The structural and magnetic properties of this compound are compared with the related compound Ba(2)YMoO(6), which is a valence bond glass.

Persistence of the Jahn–Teller distortion of Mo5+ in double perovskites: a structural study of Ba2NdMoO6 and the effect of chemical doping in Ba2Nd1−xYxMoO6

The cation-ordered perovskites Ba2NdMoO6 and Ba2Nd1−xYxMoO6 have been structurally characterised by a combination of neutron and X-ray powder diffraction. Ba2NdMoO6 retains the tetragonal room temperature structure on cooling to 150 K [I4/m; a = 5.98555(5) A, c = 8.59510(10) A] although the MoO6 octahedra distort with an elongation of two trans Mo–O bonds. Neutron diffraction data collected at T ≤ 130 K show that this compound has undergone a structural distortion to a triclinic space group, although the MoO6 octahedra do not distort any further on cooling below this temperature [at 130 K: I; 5.97625(14) A, 5.9804(2) A, 8.59650(13) A, 89.876(2)°, 89.921(3)°, 89.994(2)°]. The room temperature tetragonal space group symmetry of Ba2NdMoO6 is preserved in the series Ba2Nd1−xYxMoO6 up to composition 0.35 ≤ x < 0.5. The lattice parameters converge as the value of x increases until cubic symmetry is reached for the composition of Ba2Nd0.5Y0.5MoO6 [Fmm; a = 8.4529(3) A]. Magnetic susceptibility measurements show that all of these compounds display the Curie–Weiss behaviour associated with a fully localised electronic system. The paramagnetic moments show good agreement with those anticipated to arise from the spin-only contribution from Mo5+ (S = 1/2, µso = 1.73 µB) and the moment of 3.62 µB associated with the spin–orbit coupling of the 4I9/2 ground state of Nd3+. For x ≤ 0.125 this series shows a magnetic transition in the range 10 to 15 K indicative of a distortion of the MoO6 octahedra in these compounds that is similar to Ba2NdMoO6.

The influence of structural disorder on the magnetic properties of Sr2Fe1 − xGaxTaO6(0 ≤x≤ 1)

Powder samples of the magnetically diluted cubic perovskite phases Sr2Fe1 − xGaxTaO6 have been prepared by high temperature ceramic methods. X-Ray powder diffraction data show that the cations occupying the 6-coordinate site are chemically disordered in the range 0.10 ≤ x ≤ 0.40 and that increasing the Ga3+ concentration above this value leads to partial cation ordering between Ga3+ and Ta5+. Magnetic susceptibility data collected from these compounds can be fitted to the Curie–Weiss law, resulting in estimates of the magnetic moment per Fe3+ cation of between 4.57(1) (x = 0.20) and 6.37(1) μB (x = 0.90). The cause of the unexpectedly low paramagnetic moment observed in most of these compositions is ascribed to the effect of superexchange interactions extending beyond the adjacent 6-coordinate sites in the simple cubic lattice.