New misfit-layered cobalt oxide (CaOH)1.14CoO2

Abstract

We found a new cobalt oxide (CaOH) 1.14 CoO 2 by utilizing the high-pressure technique. X-ray and electron diffraction studies revealed that the compound has layer structure which consists of CdI 2 -type CoO 2 layers and rock-salt-type double CaOH atomic layers. The two subcells have incommensurate periodicity along the a-axis, resulting in modulated crystal structure due to the inter-subcell interaction. The structural modulation affects carrier conduction through the potential randomness. We found that the two-dimensional (2-D) variable-range hopping (VRH) regime with hole conduction is dominant at low temperature for this compound, and that the conduction mechanism undergoes crossover from the 2-D VRH regime to thermal activation-energy type one with increasing temperature. Based on the experimental results of resistivity, thermoelectric power, magnetic susceptibility and specific heat measurements, we suggested a possible electronic-band structure model to explain these results. The cobalt t 2g -derivative band crosses Fermi energy level near the band edge, yielding small finite density of localized states at the Fermi level in the band.The observed resistivity, Seebeck coefficient, large Pauli paramagnetic component in the magnetic susceptibility and comparatively small Sommerfeld constant in the specific heat are principally attributed to the holes in the t 2g -derivative band. We estimated the Wilson ratio to be about 2.8, suggesting the strong electron correlation realized in this compound.

Crystal structure and physical properties of a misfit-layered cobaltite (CaOH)1.14CoO2

“…These analysis results indicate that the oxidation state of the Co ion in the present compound is near to 3+, and its carrier doping level is less than those of the other compounds. Chemical analysis also supports this result [1]. It is worth noting that the CaOH block is remarkably deformed as compared with an ideal rock-salt structure.…”

“…The T dependence of S approaches rather metal-like one (SpT) below 220 K. In this temperature range, the T dependence is well fitted by the 1/3-power law, SpT 1/3 , which is expected in case of the two-dimensional (2-D) variable-range-hopping (VRH) regime [3]. In addition, below 270 K, the T dependence of r also well obeys the 2-D VRH-type formula, Table 1 Refined positional parameters and crystallographic data for the fundamental structure of (CaOH) 1 0.028 (2) 0.2114 (7) 1.0 a [2CaOH]k 1 CoO 2 Modulation vector k: (a 1 /a 2 )a 1 Ã Generators: (0,0,0,0)+ 1 2 ; 1 2 ; 0; 1 2 À Á + x, y, z, t; x, Ày, Àz, 1 2 þ t; 1 2 Àx, y, 1 2 À, Àt; 1 2 Àx, Ày, 1 2 +z, 1 2 Àt; Àx, Ày, Àz, Àt; Àx, y, z, 1 2 Àt; 1 2 +x, Ày, 1 2 +z, t; 1 2 +x, y, 1 2 Àz, 1 2 +t Symbol: Cmca(a00) 1ss -Cmna(a À1 0 0) 11s R wp ¼ 0:0872 rðTÞ ¼ r 0 expðT 0 =TÞ 1=3 , rather than the activation-energy type one [3]. The behavior in the low-temperature range suggests that the carrier conduction of this compound is essentially dominated by the Anderson localization, which is caused by the potential randomness due to the structural modulation in the CoO 2 layer.…”

“…The hope is that the search for new compounds will lead to an improved understanding of physics in cobalt oxides and ultimately to discovery of new superconducting materials. During the course of this search, we recently succeeded in synthesizing a new cobalt calcium hydroxide (CaOH) 1.14-CoO 2 by utilizing a high-pressure technique [1]. In this paper, we report on details of the crystal structure and transport properties of the compound.…”

Thermoelectric performance of textured Ca3−xYbxCo4O9−δ ceramics

“…As already reported, the electronic configuration of the Yb atom is 4f 14 6 s 2 , and the electronic configuration of Yb 3+ ion is 4f 13 . According to the formula, as the 4f energy level of Yb 3+ is close to the Fermi level, Yb 3+ -doping increases the density of state N v , at the same time the hole concentration p is reduced (as explained above), therefore, the Seebeck coefficient of the doped samples increases [19].…”

First-principles study of the atomic and electronic structures of misfit-layered calcium cobaltite (Ca2CoO3)(CoO2Rébola1, Klie2, Zapol3 et al. 2012Phys. Rev. B439390View full textAdd to dashboardCite

“…Incommensurately-layered cobalt oxides, [4][5][6][7][8][9] in particular Ca 3 Co 4 O 9 , (CCO), also reported as (Ca 2 CoO 3 )(CoO 2 ) 1.62 , represent one such system, where the close proximity between the layers of rocksalt (RS) Ca 2 CoO 3 and hexagonal CoO 2 results in a high in-plane Seebeck coefficient, S, and more importantly, a high thermoelectric figure of merit, ZT , at elevated temperatures. Furthermore, CCO stands out as the only layered cobalt oxide system containing one cation with nominally different oxidation states in both subsystems, namely Co 2+ in the RS layers and Co 4+ in the hexagonal CoO 2 layers.…”