Micrometer-sized single crystals of spinel-type LiCoMnO 4 were synthesized by heating a mixture of LiOH·H 2 O, CoCl 2 , and MnCl 2 with a molar ratio of Li:Co:Mn = 1.5:1:1 at 750°C. X-ray diffraction (XRD) pattern and scanning electron microscopic (SEM) image showed that LiCoMnO 4 has cubic spinel structure with well-formed octahedral crystal shapes. The size of the obtained LiCoMnO 4 single crystal particles was about 13¯m. Rietveld analysis using power XRD data confirmed the cubic spinel-type structure with space group Fd-3m, and the lattice parameter of a = 8.05812(14) ¡. The tetrahedral 8a site was occupied by both Li and Co atoms with the occupancy values of Li/Co = 0.958/0.042. Electrochemical measurement exhibited the reversible Li-ion extraction and insertion reactions at high potentials. The discharge profile with the discharge capacity of 107 mAh g ¹1 showed three voltage plateaus at 5.1, 4.9, and 3.9 V; the former two corresponded to the redox reaction of Co 3+ /Co
We investigated the Li-ion conductivity and crystal structure of the Ta-doped Li 7 La 3 M 2 O 12 (M = Hf, Sn) samples. All of the Tadoped samples exhibited a relatively high conductivity of ³10 ¹4 S cm ¹1 at room temperature, and the activation energies of Li 6.5 La 3 Hf 1.5 Ta 0.5 O 12 and Li 6.5 La 3 Sn 1.5 Ta 0.5 O 12 , which were determined from the Arrhenius plots in measured temperature range, are Ea = 0.400(6) and 0.451(1) eV, respectively. The crystal structure was analyzed by Rietveld method using powder X-ray diffraction data. From a view point of the LiO polyhedral volume in unit cell, Li 6.5 La 3 Hf 1.5 Ta 0.5 O 12 has a most suitable Li-ion environment among the Li 7 La 3 M 2 O 12 (M = Zr, Hf, Sn) compounds.
In this work, we prepared LaSrGa 1−x Mg x O 4−δ with the K 2 NiF 4 -type layered perovskite structure and then investigated the electrical conduction property and the crystal structure. From the conductivity measurements, it was indicated that LaSrGaO 4 exhibited oxide-ion conduction by substituting Mg for Ga partially, but the conductivity of the substituted sample was lower than those of LaGaO 3 -based materials reported previously. In order to clarify the reason of the lower conductivity, we performed the Rietveld and Pair Distribution Function (PDF) analyses using neutron scattering data, and also carried out first principle calculation as a theoretical approach. As a result, it was indicated the material had a two-dimensional oxide-ion conduction pathway and the oxygen vacancy tended to be localized at the corner sharing position of GaO 6 within the perovskite layer. In addition, it was suggested that the low ionic conductivity in the LaSrGaO 4 -based materials were caused by a large distortion around the defect and a large repulsive force between the oxygen vacancy and La
3+.
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