Lithium ion insertion and extraction reactions with Hollandite-type manganese dioxide free from any stabilizing cations in its tunnel cavity

Lithium ion insertion and extraction reactions with a hollandite-type α-MnO₂ specimen free from any stabilizing cations in its tunnel cavity were investigated, and the crystal structure of a Li⁺-inserted α-MnO₂ specimen was analyzed by Rietveld refinement and whole-pattern fitting based on the maximum-entropy method (MEM). The pH titration curve of the α-MnO₂ specimen displayed a monobasic acid behavior toward Li⁺, and an ion-exchange capacity of 3.25 meq/g was achieved at pH>11. The Li/Mn molar ratio of the Li⁺-inserted α-MnO₂ specimen showed that about two Li⁺ ions can be chemically inserted into one unit cell of the hollandite-type structure. As the amount of Li content was increased, the lattice parameter a increased while c hardly changed. On the other hand, the mean oxidation number of Mn decreased slightly regardless of Li content whenever ions were exchanged. The Li⁺-inserted α-MnO₂ specimen reduced topotactically in one phase when it was used as an active cathode material in a liquid organic electrolyte (1:1 EC:DMC, 1 mol/dm³ LiPF₆) lithium cell. An initial discharge with a capacity of approximately 230 mAh/g was achieved, and the reaction was reversible, whereas the capacity fell steadily upon cycling. About six Li⁺ ions could be electrochemically inserted into one unit cell of the hollandite-type structure. By contrast, the parent α-MnO₂ specimen showed a poor discharge property although no cationic residues or residual H₂O molecules remained in the tunnel space. Rietveld refinement from X-ray powder diffraction data for a Li⁺-inserted specimen of (Li₂O)_0.12MnO₂ showed it to have the hollandite-type structure (tetragonal; space group I4/m; a=9.993(11) and ; Z=8; R_wp=6.12%, R_p=4.51%, R_B=1.41%, and R_F=0.79%; S=1.69). The electron-density distribution images in (Li₂O)_0.12MnO₂ showed that Li₂O molecules almost fill the tunnel space. These findings suggest that the presence of stabilizing atoms or molecules within the tunnel of a hollandite-type structure is necessary to facilitate the diffusion of Li⁺ ions during cycling.     

Effect of doping and temperature on the crystal structure of (V1−xMox)2O3 above and below the metal/insulator transition

The crystal structure of new molybdenum-doped vanadium sesquioxides (V_1−xMo_x)₂O₃ (0?x?0.20) has been studied at low temperature (10 K) and up to room temperature, through neutron and X-ray powder diffraction. The transition from insulating I- to metallic M-type phases, either by doping or thermally driven, is accompanied by an abrupt decrease of all interatomic distances. Within each structural type however, at 10 K, the effect of doping is essentially the same as at room temperature: it increases cation-oxygen distances, and decreases cation-cation distances, making the cationic coordination octahedra more regular. Thermal effects differ for each phase type: all interatomic distances normally increase in the M-type phase (but with different octahedral modifications depending on doping), but they decrease or remain constant in the I-type phase. This produces an unusual negative thermal expansion coefficient up to 5% at low temperature for the doped compounds.     

Crystallization in ultra-thin polymer films: Morphogenesis and thermodynamical aspects

We present a computer model for polymer crystallization in ultra-thin films where chains are considered as dynamical units. In our model chains can change their internal state of order by cooperative motions to improve thermodynamic stability. The interplay between reorganization, enthalpic interactions and the morphology of crystals enables us to explain many properties of growth, morphogenesis and melting of polymer lamellae. We emphasize the relation between the thermodynamic stability of non-equilibrium crystals and morphological features which are beyond the average thickness of the lamellae. In particular, we show that melting of polymers is preceded by reorganization processes and the stability of polymer crystals is not necessarily related to the structure formed at the crystallization point. The simulations allow for the determination of some non-equilibrium properties such as the internal energy and the non-equilibrium heat capacity. We show that multiple-peak melting endotherms result from morphological transformations. The results of our computer simulations are compared with AFM observations in ultra-thin polyethyleneoxide films.     

Laser spot location method for a laser pointer interaction application using a diffractive optical element

A diffractive optical element (DOE) is applied to effectively locate a laser pointer spot on a projection screen for laser pointer interaction applications. The DOE is placed in front of a digital web camera to blur the background image while transforming the laser spot into a large diffractive pattern, such as a circle. To calculate the diffractive pattern position on the screen, only a simple subtraction method using two successive digital images with the laser ON and OFF, respectively, is needed. This approach also improves the compressed digital image transmission latency.     

Spin polarization and charge transfer of Co nanoclusters coated with CO molecules

We have investigated magnetic properties of Co clusters coated with CO molecules by first-principles density functional calculations. Total magnetic moment of the system decreases with the increase of CO molecule concentration regardless of adsorption sites for CO molecules. Spin polarization slightly increases as CO molecules are adsorbed on the most stable sites of Co cluster, which is caused by the increased local spin polarization of p-electrons due to charge transfer from Co clusters to CO molecules.     

Anomalous effects in charging of Pd powders with high density hydrogen isotopes

A twin system for hydrogen absorption experiments has been constructed to replicate the phenomenon of heat and ⁴He generation by D₂ gas absorption in nano-sized Pd powders reported by Arata and Zhang, and to investigate the underlying physics. For Pd⋅Zr oxide nano-powders, anomalously large energies of hydrogen isotope absorption, 2.4±0.2 eV/D-atom and 1.8±0.4 eV/H-atom, as well as large loading ratio of D/Pd=1.1±0.0 and H/Pd=1.1±0.3, respectively, were observed in the phase of deuteride/hydride formation. The sample charged with D₂ also showed significantly positive output energy in the second phase after the deuteride formation.     

Complex dynamics of cellular automata rule 119

In this paper, the dynamical behaviors of cellular automata rule 119 are studied from the viewpoint of symbolic dynamics in the bi-infinite symbolic sequence space Σ₂. It is shown that there exists one Bernoulli-measure global attractor of rule 119, which is also the nonwandering set of the rule. Moreover, it is demonstrated that rule 119 is topologically mixing on the global attractor and possesses the positive topological entropy. Therefore, rule 119 is chaotic in the sense of both Li-Yorke and Devaney on the global attractor. It is interesting that rule 119, a member of Wolfram’s class II which was said to be simple as periodic before, actually possesses a chaotic global attractor in Σ₂. Finally, it is noted that the method presented in this work is also applicable to studying the dynamics of other rules, especially the 112 Bernoulli-shift rules therein.     

Compact and noncompact structures for nonlinear fractional evolution equations

This Letter deals with compact and noncompact solutions for nonlinear evolution equations with time-fractional derivatives. We present a reliable approach of the homotopy perturbation method to handle nonlinear fractional evolution equations. The validity of the approach is verified through illustrative examples. New exact solitary wave and compacton solutions are developed. The proposed technique could lead to a promising approach for a wide class of nonlinear fractional evolution equations.