The misfit compound [CoO2][Ca2CoO3−δ]0.62 is well-known for its good potentialities in the field of thermoelectric oxides combining good electronic transport, high Seebeck coefficient, and low thermal conductivity. Its 2D-crystal structure can be regarded as a natural intergrowth between electronic-conducting Co3+/Co4+ hexagonal layers and oxygen deficient Co2+/Co3+ rock-salt layers with low thermal conductivity. Their lacunar character suggests a possible anionic conductivity. We took advantage of this model for application as a SOFC cathode material. Additional advantages appear from the good chemical and mechanical adaptability (TEC = 9−10 × 10−6 °C−1) with intermediate temperature electrolyte, namely, CGO. The manufactured symmetrical cells show a good electrode/electrolyte adherence, stable after long-time experiments. Our promising preliminary electrochemical tests show a rather low electrode overpotential (4Ω·cm2) for ∼40 μm thick layers with a rather dense microstucture. The porosity and electric performances are improved in the composite with 30 wt % CGO (∼1 Ω·cm2). In general, from polarization experiments versus temperature and oxygen pressure, we found two distinct processes, frequency-separated, that is, HF, charge transfer at the TPB with intrinsic O2− diffusion; LF, gas transfer/oxygen dissociation. This latter is largely fastened in the CGO/Ca3Co4O9−δ, reminiscent of the existing but limiting ionic mobility in the single phase of the title compound.

In order to find out more about the suppression of ferromagnetic (FM) interactions in Sr1-xLaxRuO3, electronic structures and magnetic properties have been investigated upon changing x from 0.0 to 0.5, using an XRD method with Rietveld analysis, a SQUID magnetometer and a DV-Xα computational method. In comparison with magnetic properties in Sr1-xCaxRuO3, FM interactions in Sr1-xLaxRuO3 are found to be suppressed very rapidly against x. Neither structural distortion nor cation-size disorder can account for such rapid suppression. Instead, this may be attributed to the effect of La-O hybridization created by La substitution for Sr. This hybridization effect weakens the FM order around Ru ions and, as a result, the long-range FM states are suppressed even if x is small. The DV-Xα cluster method was employed to estimate the energy difference between the up and down spin density of states in SrRuO3 and Sr0.5La0.5RuO3. This calculation predicts that Sr1-xLaxRuO3 contains La-O hybridization which suppresses FM interaction even at small x.

Low temperature dielectric properties of YMn 0.95 Ru 0.05 O 3 AIP Conf. Correlation between high ionic conductivity and twin structure of La 0.95 Sr 0.05 Ga 0.9 Mg 0.1 O 3 − δ Nature of small-polaron hopping conduction and the effect of Cr doping on the transport properties of rare-earth manganite La 0.5 Pb 0.5 Mn 1−x Cr x O 3In order to identify the carrier responsible for the electrical transport at room temperature in LiMn 2 O 4 from the viewpoint of practical applications as a cathode material, the bulk conductivity measurements by complex-plane impedance analyses have been carried out on LiMn 2 O 4 , Li 0.95 Mn 2 O 4 , and LiMn 1.95 B 0.05 O 4 ͑BϭAl 3ϩ or Ga 3ϩ ͒ together with the measurements of four-probe dc conductivities and dielectric relaxation processes, because these are two candidates for the carrier, a Li ion or a nonadiabatic small polaron of an e g electron on Mn 3ϩ . The comparison of the ionic conductivity estimated numerically from the parameters obtained experimentally for the Li-diffusion in LiMn 2 O 4 with the bulk conductivity indicates that the Li-diffusion seems difficult to play the primary role in the electrical conduction. Instead, a hopping-process of nonadiabatic small polarons of e g electrons is likely to dominate predominantly the electrical transport properties. The dielectric relaxation process, and the activation energies and the pre-exponential factors of the bulk conductivities in Li 0.95 Mn 2 O 4 and LiMn 1.95 B 0.05 O 4 are explained self-consistently in terms of the polaronic conduction.

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Electrical transport properties of polycrystalline ceramic specimens of the system (x = 0.05, 0.10, and 0.15) have been investigated as functions of temperature by means of complex-plane impedance analysis, dielectric properties, four-probe dc conductivity, Seebeck coefficients, and magnetic susceptibilities. The type of the majority carrier changes from electrons to holes when x increases from 0.10 to 0.15, because the Seebeck coefficient changes from negative to positive with x increasing from 0.10 to 0.15. The complex-plane impedance analysis distinguishes the bulk conduction from the conduction across grain boundaries. In a specimen with x = 0.15, the activation energy in the bulk conduction is nearly equal to that for the dielectric relaxation. This implies that the hopping process of small polarons of holes dominates the transport properties in this specimen above 190 K. The temperature dependencies of the magnetic susceptibilities indicate that the number of high-spin ions (S = 2) decreases with increasing x. The expansion of the lattice parameters and the increment of the ratio with increasing x suggest that ions are preferentially substituted for low-spin , which relaxes the rhombohedral structural distortion in the system. The change in the type of the charge carrier has been discussed in terms of the electronic structures deduced from these experimental results.

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Electronic structures in the metallic VO 2 phase above the metal-insulator ͑MI͒ transition temperature of T c and the insulating phase below T c have been investigated using the combination of the three-dimensional periodic shell model and the discrete-variational ͑DV͒-X␣ cluster method. Besides the correlation effect for d ʈ electrons, the Hamiltonian in the insulating phase includes the Anderson's attractive potential due to the electron-phonon interactions which stabilize the three-dimensional periodic distribution of V 4ϩ-V 4ϩ dimers. The shell model estimates the electron-phonon coupling constant and provides direct theoretical evidence that the dimers are stable in the low-temperature phase. The DV-X␣ cluster method calculates the electron energies in ͓V 2 O 10 ͔ Ϫ12 clusters and the value for the intersite repulsive nearest-neighbor d-d Coulombic interaction which quantifies the correlation effect for d ʈ electrons. The electron-phonon interaction effect and the correlation effect for d ʈ electrons are found to split d band into the empty upper and the occupied lower Hubbard bands and also to result in an obvious energy gap between these bands in the insulating phase. In the metallic phase, the nonresolved d band overlaps the * band and they construct a partially filled conduction band. These calculations explain well the MI transition in VO 2 and, in particular, the electron-phonon interaction assessed by the periodic shell model is an indispensable contribution in the stabilization of the insulating phase. ͓S0163-1829͑97͒01003-5͔