Search

Improved methods for the flux growth of single crystals of the important battery material LiFePO4 have been developed, allowing the facile preparation of single crystals up to 1 cm across with well-developed facets at relatively low temperatures. The structural characterization of these samples by both powder X-ray diffraction and single crystal diffraction (X-ray and neutron) indicates that the samples are typically stoichiometric with a very low concentration of Fe defects on the Li site, though crystals with larger concentrations of defects can be specifically grown using Fe-rich fluxes. These defects occur through the formation of a Fe-rich (Li1-2xFe x)FePO4 partial solid solution, in contrast to the antisite defects more commonly discussed in the literature which would preserve the ideal LiFePO4 stoichiometry. The LiFePO4 defects are shown to be sarcopside-like (2 Li+ → Fe2+ + vacancy) based on compositions refined from single crystal diffraction data, the observed dependence of unit cell parameters on defect concentration, and their observed phase behavior (defects only appear in growths from fluxes which are Fe-rich relative to stoichiometric LiFePO4). The distribution of defects has been studied by aberration corrected scanning transmission electron microscopy and was found to be highly inhomogenous, suggesting that defect-containing crystals may consist of endotaxial intergrowths of olivine LiFePO4 and sarcopside Fe3(PO4)2 in a manner that minimizes the detrimental influence of FeLi defects on the rate of Li-ion transport within crystallites. © 2013 American Chemical Society.

The ground state magnetic structure is characterized by a magnetic wave vector k=(0.115,0,0). The onset of antiferromagnetic order occurs around 12k with an inflection in the temperature dependence of the magnetic intensities at about 8K.

We report on single-crystal neutron diffraction studies of the local-moment antiferromagnet CeCuSn. The ground-state magnetic structure is characterized by a magnetic wave vector k =(0.115,0,0). The onset of antiferromagnetic order occurs around 12 K with an inflection in the temperature dependence of the magnetic intensities at about 8 K. This is in contrast to bulk measurements, which only show broad features at 8-10 K. The ordered moments are likely reduced from the free-ion moment for Ce. [ABSTRACT FROM AUTHOR]

Single crystals of a new multinary chromium carbide, La21Cr8-2aAlbGe7-bC12 (henicosa­lanthanum octa­chromium aluminium hexa­germanium dodeca­carbide), were grown from an La-rich self flux and were characterized by single-crystal X-ray diffraction. The face-centered cubic crystal structure is composed of isolated and geometrically frustrated regular Cr tetra­hedra that are co-centered within regular C octa­hedra. These mutually separated Cr4-aC6 clusters are distributed throughout a three-dimensional framework of Al, Ge, and La. The title compound is isotypic with La21-Mn8X7C12 and R21Fe8X7C12 (R = La, Ce, Pr; X = Al, Bi, Ge, Sn, Sb, Te) and represents the first example of a Cr-based compound with this structure-type. [ABSTRACT FROM AUTHOR]

Improved methods for the flux growth of single crystals of the important battery material LiFePO4 have been developed, allowing the facile preparation of single crystals up to 1 cm across with well-developed facets at relatively low temperatures. The structural characterization of these samples by both powder X-ray diffraction and single crystal diffraction (X-ray and neutron) indicates that the samples are typically stoichiometric with a very low concentration of Fe defects on the Li site, though crystals with larger concentrations of defects can be specifically grown using Fe-rich fluxes. These defects occur through the formation of a Fe-rich (Li1-2xFex)FePO4 partial solid solution, in contrast to the antisite defects more commonly discussed in the literature which would preserve the ideal LiFePO4 stoichiometry. The LiFePO4 defects are shown to be sarcopside-like (2 Li+ ? Fe2+ + vacancy) based on compositions refined from single crystal diffraction data, the observed dependence of unit cell parameters on defect concentration, and their observed phase behavior (defects only appear in growths from fluxes which are Fe-rich relative to stoichiometric LiFePO4). The distribution of defects has been studied by aberration corrected scanning transmission electron microscopy and was found to be highly inhomogenous, suggesting that defect-containing crystals may consist of endotaxial intergrowths of olivine LiFePO4 and sarcopside Fe3(PO4)2 in a manner that minimizes the detrimental influence of FeLi defects on the rate of Li-ion transport within crystallites. [ABSTRACT FROM AUTHOR]

The crystal structure of the promising Li-ion battery cathode material LiFeBO3 has been redetermined based on the results of single crystal X-ray diffraction data. A commensurate modulation that doubles the periodicity of the lattice in the a-axis direction is observed. When the structure of LiFeBO3 is refined in the 4-dimensional superspace group C2/ c(α0γ)00, with α = 1/2 and γ = 0 and with lattice parameters of a = 5.1681 Å, b = 8.8687 Å, c = 10.1656 Å, and β = 91.514°, all of the disorder present in the prior C2/c structural model is eliminated and a long-range ordering of 1D chains of corner-shared LiO4 is revealed to occur as a result of cooperative displacements of Li and 0 atoms in the c-axis direction. Solid-state hybrid density functional theory calculations find that the modulation stabilizes the LiFeBO3 structure by 1.2 kJ/mol (12 meV/f.u.), and that the modulation disappears after delithiation to form a structurally related FeBO3 phase. The band gaps of LiFeBO3 and FeBO3 are calculated to be 3.5 and 3.3 eV, respectively. Bond valence sum maps have been used to identify and characterize the important Li conduction pathways, and suggest that the activation energies for Li diffusion will be higher in the modulated structure of LiFeBO3 than in its unmodulated analogue. [ABSTRACT FROM AUTHOR]

Large single crystals of LiFePO4 (up to 1 cm diagonal) are obtained besides Li3PO4 and Fe2ClPO4 by the flux growth method using Li3PO4, LiCl, FeCl2, and LiFePO4 as starting materials (graphite crucible, 810 °C, 2 h). [ABSTRACT FROM AUTHOR]

Single crystals of a new multinary chromium carbide, La 21 Cr 8-2 a Al b Ge 7- b C 12 (henicosa-lanthanum octa-chromium aluminium hexa-germanium dodeca-carbide), were grown from an La-rich self flux and were characterized by single-crystal X-ray diffraction. The face-centered cubic crystal structure is composed of isolated and geometrically frustrated regular Cr tetra-hedra that are co-centered within regular C octa-hedra. These mutually separated Cr 4-a C 6 clusters are distributed throughout a three-dimensional framework of Al, Ge, and La. The title compound is isotypic with La 21-δ Mn 8 X 7 C 12 and R 21 Fe 8 X 7 C 12 ( R = La, Ce, Pr; X = Al, Bi, Ge, Sn, Sb, Te) and represents the first example of a Cr-based compound with this structure-type.