Electronic structure and electron energy-loss spectra of Sr0.35CoO2

Abstract

The electronic structure of Sr 0.35 CoO 2 , structurally analogous to the layered Na x CoO 2 , has been evaluated using the local spin density approximation (LSDA). We find that evident c-dispersions appear in both the e ' g and a 1g Co-derived bands, demonstrating the existence of a notable interplanar interaction in Sr 0.35 CoO 2 . The LSDA+U calculation reveals that the electronic structure, in particular the band splitting between the spin-up and spin-down electrons, changes evidently along with the increase of the effective on-site Coulomb interaction U. Analysis of theoretical and experimental electron energy-loss spectra (EELS) for the oxygen K-edge and the Co L 23 -edge suggests that the on-site interaction (U) in Sr 0.35 CoO 2 is less than 3eV which is noticeably weaker than the estimated value (from 5eV to 8eV) in the Na x CoO 2 materials.

Low-temperature magnetic and transport properties of layered(Sr,Ca)xCoO2single crystals

“…3͑a͒, both ab and c exhibit metallic behaviors in the whole temperature range, consistent with the band structure calculation. 27 The ab behavior is qualitatively the same as that in polycrystalline Sr 0.35 CoO 2 samples. 17,15 At room temperature the resistivity is only slightly anisotropic with c Ϸ 6 ab , in agreement with an anisotropic ratio c / ab Ϸ 3 for Na 0.71 CoO 2 crystal and a resistivity anisotropy ͑ c / ab ͒ of 8 by electronic structure calculations for NaCo 2 O 4 .…”

“…Moreover, a band structure calculation of Sr 0.35 CoO 2 reveals evident c dispersions, demonstrating the existence of a notable interplanar interaction. 27 This implies Sr 0.35 CoO 2 is highly three dimensional. The slight resistivity anisotropy of Sr 0.35 CoO 2 may be correlated with this relative isotropic interaction.…”

Low-temperature magnetic and transport properties of layeredSrxCoO2

“…17 The resistivity of Sr 0.35 CoO 2 is 8.83 m⍀ cm at 300 K. This agrees with the data published by Ishikawa et al 16 The resistivity of Sr 0.35 CoO 2 is larger than that of ␥-Na 0.7 CoO 2 over the whole temperature range.…”

“…Its Seebeck coefficient is comparable to that of ␥-Na 0.7 CoO 2 , and the resistivity shows a metallic behavior, in agreement with the band-structure calculation. 17 Structural analysis suggested that Sr x CoO 2 has hexagonal symmetry, similar to ␥ -Na x CoO 2 ͑P6 3 / mmc͒. Two superstructures arising respectively from the ordering of intercalated Sr and a periodic structural distortion were observed in Sr 0.35 CoO 2 .…”

“…[11][12][13][14][15][16][17][18] Ryuji Ishikawa et al 16 first synthesized ␥-Sr 0.35 CoO 2 by a low-temperature ion exchange technique from a ␥-Na 0.7 CoO 2 precursor and studied its transport and thermoelectric properties. Sr 0.35 CoO 2 possesses a similar crystal structure as Na x CoO 2 .…”