Related papers: Sodium Ion Ordering in NaxCoO2
We report a systematic study of the $c$ lattice parameter in the Na$_{x}$CoO$_{2}$ phases versus Na content $x>0.5$, in which sodium always displays ordered arrangements. This allows us to single out the first phase which exhibits an AF…
We have utilized neutron powder diffraction to probe the crystal structure of layered Na$_{x}$CoO$_{2}$ near the half doping composition of $x=$0.46 over the temperature range of 2 to 600K. Our measurements show evidence of a dynamic…
The crystal structures of the NaxCoO2 phases based on three-layer NaCoO2, with x=0.32, x=0.51, x=0.60, x=0.75 and x=0.92, determined by powder neutron diffraction, are reported. The structures have triangular CoO2 layers interleaved by…
Layered Sr0.35CoO2 has been synthesized by means of an ion exchange reaction from Na0.7CoO2. Resistivity measurements show that this material can be either metallic or semiconducting depending on the annealing conditions. Magnetic…
Neutron and x-ray powder diffraction have been used to investigate the crystal structures of a sample of the newly-discovered superconducting sodium cobaltate deuterate compound with composition Na0.31(3)CoO2o1.25(2)D2O and its anhydrous…
Here we present results of accurate wet-chemical redox analyses, revealing that the oxidation number of cobalt in the newly discovered CoO2-layer superconductor, NaxCoO2 yH2O (x ~ 0.36, y ~ 1.3) is ~ 3.46. This value is significantly lower…
From 59Co and 23Na NMR, we demonstrate the impact of the Na+ vacancy ordering on the cobalt electronic states in Na0.75CoO2: at long time scales, there is neither a disproportionation into 75 % Co3+ and 25 % Co4+ states, nor a mixed-valence…
The CoO$_{2}$ layers in sodium-cobaltates Na$_{x}$CoO$_{2}$ may be viewed as a spin $S=1/2$ triangular-lattice doped with charge carriers. The underlying physics of the cobaltates is very similar to that of the high $T_{c}$ cuprates. We…
Charge ordering of V4+ and V5+ in NaV2O5 has been studied by an X-ray diffraction technique using anomalous scattering near a vanadium K-absorption edge to critically enhance a contrast between the two ions. A dramatic energy dependence of…
Transmission-electron-microscopy investigation reveals the presence of a superstructure with a doubled period of 2d110 in the NaxCoO2 materials for x ranging from 0.75 to 1.0. Systematic analyses suggest that this superstructure in general…
Recently the unusual metallic state with a substantially non-uniform distribution of a charge and mag\-ne\-tic density in CoO$_2$ planes was found experimentally in the Na$_x$CoO$_2$ compound with $x>0.6$. We have investigated an origin of…
The structural properties of NaxCoO2 and NaxCoO2yH2O have been investigated. The NaxCoO2yH2O samples in general show up the superconducting transitions at around 3.5K. EDAX analyses suggest our samples have the average composition of…
We have grown single crystals of Na$_x$Ca$_y$CoO$_2$ and determined their superstructures as a function of composition using neutron and x-ray diffraction. Inclusion of Ca$^{2+}$ stabilises a single superstructure across a wide range of…
Using a combination of low-temperature nanocalorimetry and x-ray diffraction we identify three temperature regimes characterized by distinct Na ordering patterns (low temperature up to 290 K, intermediate 290-340 K, and high above 340 K).…
We elucidate the thermodynamics of sodium (Na) intercalation into the sodium super-ionic conductor (NaSICON)-type electrode, Na$_x$V$_2$(PO$_4$)$_3$, for promising Na-ion batteries with high-power density. This is the first report of a…
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…
Synchrotron X-ray diffraction investigations of two single crystals of Na_xCoO_2 from different batches with composition x = 0.525-0.530 reveal homogeneous incommensurate sodium ordering with propagation vector (0.53 0.53 0) at…
The crystal structure and oxygen stoichiometry in two-layer Na0.74CoO2 and Na0.38CoO2 at room temperature are analyzed by powder neutron diffraction. Two sets of diffraction data for each sample, taken at different incident neutron…
We have compared by $^{23}$Na NMR and magnetic susceptibility the magnetic properties of oriented powder samples of Na$_{x}$CoO$_{2}$ compounds. The NMR spectra are found identical for various samples with nominal $0.50\leq x\leq 0.70,$…
We report the observation of a stepwise "melting" of the low-temperature Na-vacancy order in the layered transition metal oxide Na0.7CoO2. High-resolution neutron powder diffraction indicates the existence of two first-order structural…