RESUMEN

Magnetite (Fe3O4) is an abundant, low cost, environmentally benign material with potential application in batteries. Recently, low temperature coprecipitation methods have enabled preparation of a series of nanocrystalline magnetite samples with a range of crystallite sizes. Electrochemical cells based on Li/Fe3O4 show a linear increase in capacity with decreasing crystallite size at voltages ≥1.2 V where a 2× capacity improvement relative to commercial (26.2 nm) magnetite is observed. In this report, a combination of X-ray powder diffraction (XRD) and X-ray absorption spectroscopy (XAS) is used to measure magnetite structural changes occurring upon electrochemical reduction, with parent Fe3O4 crystallite size as a variable. Notably, XAS provides evidence of metallic iron formation at high levels of electrochemical reduction.

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RESUMEN

Silver vanadium phosphorous oxides (AgwVxPyOz) are notable battery cathode materials due to their high energy density and demonstrated ability to form in-situ Ag metal nanostructured electrically conductive networks within the cathode. While analogous silver vanadium diphosphate materials have been prepared, electrochemical evaluations of these diphosphate based materials have been limited. We report here the first electrochemical study of a silver vanadium diphosphate, Ag2VP2O8, where the structural differences associated with phosphorous oxides versus diphosphates profoundly affect the associated electrochemistry. Reminiscent of Ag2VO2PO4 reduction, in-situ formation of silver metal nanoparticles was observed with reduction of Ag2VP2O8. However, counter to Ag2VO2PO4 reduction, Ag2VP2O8 demonstrates a significant decrease in conductivity upon continued electrochemical reduction. Structural analysis contrasting the crystallography of the parent Ag2VP2O8 with that of the proposed Li2VP2O8 reduction product is employed to gain insight into the observed electrochemical reduction behavior, where the structural rigidity associated with the diphosphate anion may be associated with the observed particle fracturing upon deep electrochemical reduction. Further, the diphosphate anion structure may be associated with the high thermal stability of the partially reduced Ag2VP2O8 materials, which bodes well for enhanced safety of batteries incorporating this material.

RESUMEN

Synthetic control of the silver content in silver hollandite, Ag(x)Mn(8)O(16), where the silver content ranges from 1.0 ≤ x ≤ 1.8 is demonstrated. This level of compositional control was enabled by the development of a lower temperature reflux based synthesis compared to the more commonly reported hydrothermal approach. Notably, the synthetic variance of the silver content was accompanied by a concomitant variance in crystallite size as well as surface area and particle size. To verify the retention of the hollandite structure, the first Rietveld analysis of silver hollandite was conducted on samples of varying composition. The impacts of silver content, crystallite size, surface area, and particle size on electrochemical reversibility were examined under cyclic voltammetry and battery testing.

RESUMEN

Single crystals of K(4)Cu(MoO(4))(3) and nonmagnetic K(4)Zn(MoO(4))(3) have been grown by the flux-growth method. K(4)Cu(MoO(4))(3) can be described as a quantum quasi-1-d antiferromagnet with correlations between neighboring Cu(2+) ions but no magnetic long-range ordering down to 0.4 K. Comparison of the structure and magnetic properties of isostructural A(4)Cu(MoO(4))(3) (A = K, Rb) allows the isolation of the effects of low dimensionality from structural distortion along the Cu-O-Mo chains. The characteristic one-dimensional behavior is hence suppressed to lower the temperature in K(4)Cu(MoO(4))(3) in comparison with that of the Rb analogue. For example, a broad peak in the specific heat is observed ~2.3 K at 0 T, which is consistent with the onset of the quantum spin liquid state.

RESUMEN

The title compound, C(33)H(24)O(6)·0.17H(2)O, which is commonly known as (SR,SR,SR)-trimethyl 1,10,19-truxentricarboxyl-ate, crystallizes as a hydrate with the water mol-ecule encapsulated between three ester groups by O-H⋯O hydrogen bonding to two of them. The water mol-ecule site is not fully occupied in the crystal studied, with a refined site occupancy of 0.167 (5). The 27-atom ring system is approximately planar, with a maximum deviation of 0.148 (1) Å, and the three ester substituents are all on the same side of this plane.