Nik Reeves-McLaren

Crystal structure determination by combined synchrotron powder X-ray diffraction and crystal structure prediction: 1 : 1 L-ephedrine D-tartrate

The crystal structure of the diastereomeric salt 1 : 1 L-ephedrine D-tartrate (1 : 1 LD, C10H16NO+·C4H5O6−) was determined from high-resolution synchrotron powder X-ray diffraction (PXRD) data using global optimization in direct space (parallel tempering) together with computational modelling to locate hydrogen positions and refined by the Rietveld method. The structure is monoclinic, space group P21, with a = 18.82810(3) A, b = 7.19429(2) A, c = 5.73035(1) A, β = 95.9613(1)°, V = 772.006(3) A3, and Z = 2. Computational prediction of organic salt structures, especially hydrogen positions, is a valuable complementary technique to PXRD for the final stages of structure determination.

Spinel–rock salt transformation in LiCoMnO4−δ

The transformation on heating LiCoMnO4, with a spinel structure, to LiCoMnO3, with a cation-disordered rock salt structure, accompanied by loss of 25% of the oxygen, has been followed using a combination of diffraction, microscopy and spectroscopy techniques. The transformation does not proceed by a topotactic mechanism, even though the spinel and rock salt phases have a similar, cubic close-packed oxygen sublattice. Instead, the transformation passes through two stages involving, first, precipitation of Li2MnO3, leaving behind a Li-deficient, Co-rich non-stoichiometric spinel and, second, rehomogenization of the two-phase assemblage, accompanied by additional oxygen loss, to give the homogeneous rock salt final product; a combination of electron energy loss spectroscopy and X-ray absorption near edge structure analyses showed oxidation states of Co2+ and Mn3+ in LiCoMnO3. Subsolidus phase diagram determination of the Li2O-CoOx-MnOy system has established the compositional extent of spinel solid solutions at approximately 500°C.

Synthesis and Characterization of Li11Nd18Fe4O39−δ

Li(11)Nd(18)Fe(4)O(39-δ) has been synthesized by the solid-state reaction of pellets, covered with powder of the same composition to avoid lithium loss, with a final reaction temperature of 950 °C. This phase has been reported previously to have various stoichiometries: Li(5)Nd(4)FeO(10), Li(8)Nd(18)Fe(5)O(39), and Li(1.746)Nd(4.494)FeO(9.493). The crystal structure of Li(11)Nd(18)Fe(4)O(39-δ) is closely related to that reported previously for two of the other three compositions but contains extra Li and differences in Li/Fe site occupancies. Fe is present in a mixture of 3+ and 4+ oxidation states, as confirmed by Mössbauer spectroscopy. The oxygen content of 39 - δ is variable, depending on the processing conditions. Samples slow-cooled in air from 800 °C are semiconducting, attributed to the presence of Fe(4+) ions, whereas samples quenched from 950 °C in N(2) are insulating.

Synthesis, structure and electrical properties of N-doped Li3VO4

N-doped Li3VO4 of general formula Li3+xVO4−xNx was prepared by solid state reaction of Li3N, V2O5 and either Li2CO3 or LiOH·H2O. A solid solution based on the low temperature β polymorph of Li3VO4 was obtained with composition 0 ≤ x ≤ 0.2. Structural studies by X-ray and neutron powder diffraction confirmed the partial replacement of oxygen on the O(1) sites by N together with creation of an equal number of Li+ ions which are located off-centre in adjacent octahedral Li(3) sites. Electrical property measurements on sintered pellets using impedance spectroscopy showed that the solid solutions are modest conductors of Li+ ions, consistent with the partial occupancy of Li+ ions in the interstitial octahedral sites. The activation energy for conduction of samples prepared using LiOH·H2O, ∼1.91 eV, is much greater than for samples prepared at higher temperature, using Li2CO3, ∼0.78 eV; it is speculated that this is due to ion trapping in Lii˙/N0′ defect clusters. This study represents a relatively new method for doping Li+ ions into a structure by aliovalent anion doping: partial replacement of O by N is compensated by creation of interstitial Li+ ions.

Magnetic and Structural Characterization of NiFe/Fe 30 Co 70 Bilayers

Magnetostrictive films are required for a wide range of device applications; by increasing the magnetostriction constant and decreasing the anisotropy field, the devices will become more efficient. This paper has studied Fe₃₀Co₇₀ films on different thicknesses of the soft magnetic underlayer Ni₈₁Fe₁₉, to determine how the structural and magnetic properties change. It was found that the anisotropy field of the Fe₃₀Co₇₀ film could be reduced by 50% to 10 kA/m and the magnetostriction constant increased by a factor 4 to 65 ppm when grown on 30 nm Ni₈₁Fe₁₉. This was due to the NiFe underlayer inducing a BCC(110) texture within the Fe₃₀Co₇₀ film and reducing the in-plane stress.

Biotemplating: A Sustainable Synthetic Methodology for Na-ion Battery Materials

Dextran biotemplating is a novel, sustainable and reduced-temperature synthetic approach that allows a high level of control over the size and shape of particles formed. This article discusses the application of this technique to the synthesis of an important candidate sodium-ion positive electrode material, Na2/3Ni1/3Mn2/3O2 (or ‘NNM’), with a high theoretical specific capacity (173 mA h g−1). While a solid state reference sample prepared at 850 °C exhibited a specific capacity of ∼80 mA h g−1 after 10 cycles, samples made via our dextran biotemplating route with final calcination at 550 °C for 12 h showed a large and significant improvement at 103.1 mA h g−1, under the same operating conditions.