Related papers: Pressure effects in the triangular layered cobalti…

Recent studies exposed many remarkable properties of layered cobaltates NaxCoO2. Surprisingly, many-body effects have been found to increase at sodium-rich compositions of NaxCoO2 where one expects a simple, nearly free motion of the dilute…

The observed correlation of oxygen vacancies and room temperature ferromagnetic ordering in Co doped ZnO1-o nanoparticles reported earlier (Naeem et al Nanotechnology 17, 2675-2680) has been further explored by transport and optical…

Using muon spin spectroscopy we have found that, for both Na$_x$CoO$_2$ (0.6 $\leq x \leq$ 0.9) and 3- and 4-layer cobaltites, a common low temperature magnetic state (which in some cases is manifest as an incommensurate spin density wave)…

From 59Co and 23Na NMR, we demonstrate the impact of the Na+ vacancy ordering on the cobalt electronic states in Na0.75CoO2: at long time scales, there is neither a disproportionation into 75 % Co3+ and 25 % Co4+ states, nor a mixed-valence…

Sodium cobaltate with high Na content is a promising thermoelectric material. It has recently been reported that oxygen vacancies can alter the material properties, reducing its figure of merit. However, experimental data concerning the…

Magnetism of layered cobaltites Na$_x$CoO$_2$ with $x$ = 0.6 and 0.9 has been investigated by a positive muon spin rotation and relaxation ($\mu^+$SR) spectroscopy together with magnetic susceptibility and specific heat measurements, using…

In this work we present the result of the first experimental investigation of the role of oxygen content on the properties of the HoBaCo2O5+delta layered cobaltite. We have measured the variation of oxygen content as a function of…

The layered cobaltite [Ca$_2$CoO$_3$]$_{0.62}$[CoO$_2$], often expressed as the approximate formula Ca$_3$Co$_4$O$_9$, is a promising candidate for efficient oxide thermoelectrics but an origin of its unusual thermoelectric transport is…

We report 23Na NMR studies of the polycrystalline samples of double-layer hydrated cobalt oxides NaxCoO2.yH2O (x ~ 0.35 and y ~ 1.3) with the superconducting transition temperatures Tc < 1.8K and ~4.5K, and the dehydrated NaxCoO2 (x ~…

We present infrared ab-plane conductivity data for the layered cobaltate Na$_x$CoO$_2$ at three different doping levels ($x=0.25, 0.50$, and 0.75). The Drude weight increases monotonically with hole doping, $1-x$. At the lowest hole doping…

The effect of the 16O-->18O substitution on the superconducting transition temperatures Tc of NaxCoO2.yH2O has been studied for several sets of samples. Each set has two kinds of samples, one with the oxygen sites in the CoO2 layers filled…

We present precise measurements of the upper critical field (Hc2) in the recently discovered cobalt oxide superconductor. We have found that the critical field has an unusual temperature dependence; namely, there is an abrupt change of the…

The effect of pressure on superconductivity of 111 type NaxFeAs is investigated through temperature dependent electrical resistance measurement in a diamond anvil cell. The superconducting transition temperature (Tc) increases from 26 K to…

We report T_c and ^{59}Co nuclear quadrupole resonance (NQR) measurements on the cobalt oxide superconductor Na_{x}CoO_{2}\cdot 1.3H_{2}O (T_c=4.8 K) under hydrostatic pressure (P) up to 2.36 GPa. T_c decreases with increasing pressure at…

Transmission electron microscopy observations reveal the presence of complex superstructures and remarkable phase separation in association with Na-ordering phenomenon in y-Na0.5CoO2. Resistivity and magnetization measurements indicate that…

Vanadium oxides have been highly attractive for over half a century since the discovery of the metal insulator transition near room temperatures. Here NaxVO2 is studied through a systematic comparison with other layered sodium metal oxides…

Ca2-xNaxCuO2Cl2 is a structural analogue to the La2-xSrxCuO4 superconductor. By substituting Na+ for Ca2+ mobile holes are introduced into the CuO2 planes. A series of experiments shows that the Na content x depends not only on the pressure…

The pressure dependence of phase transitions in the quasi one-dimensional vanadium oxide $\beta$-Na$_{1/3}$V$_2$O$_5$ has been studied by magnetic susceptibility and electrical resistivity measurements. The pressure dependence of the…

Results of thermo-electric power (S) and electrical resistivity (r) measurements are reported on NaxCoO2 compounds with x = 1.0, 0.7 and 0.6. These are single-phase compounds crystallizing in the hexagonal structure (space group P63/mmc) at…

We report the measurements of thermopower, electrical resistivity and thermal conductivity in a complex cobalt oxide Li$_{0.48}$Na$_{0.35}$CoO$_{2}$, whose crystal structure can be viewed as an intergrowth of the O3 phase of…