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Abstract: Theoretical impedance relationships in a limiting process with non-steady-state surface diffusion were derived based on the interfacial conductivity concept at the interface between an oxygen ion conductor and a metallic electrode. While the non-steady-state surface diffusion of adsorbed neutral oxygen on the metallic electrode could be described by Fick's second law, approximated and equivalent equations to the Warburg impedance and Gerischer impedance were derived according to the boundary conditions and occurrence of dissipation by the chemical reaction. The diffusion related to the electrochemical impedance signal is not the diffusion of the oxygen ions. In addition, it is not necessary to assume an electrochemical potential gradient or profile of the free electrons in the metallic electrode. The relationships obtained in this paper indicate that electrochemical potential measured by an instrument is clearly defined by the electrochemical potential of free electrons at the triple phase boundary. The meaning of the equivalent electrical circuits corresponding to the impedance spectra is reconsidered from the view points of the interfacial conductivity concept. [Copyright &y& Elsevier]

Abstract: We investigated the effect of subgrain boundaries on periodic domain-inverted structures with a period of ∼30μm in near-stoichiometric LiTaO3 (SLT) crystals and found that they negligibly affected the structures. Using SLT crystals having subgrain boundaries and a quasi-phase matching technique, we fabricated a 2-mm-thick, 60-mm-long periodically poled SLT frequency converter with a domain-inverted structure with a 30.5-μm period and demonstrated optical parametric oscillation. [Copyright &y& Elsevier]

Abstract: Metal chalcogenide-based mixed ionic–electronic conductors such as Ag2S and Cu2S can be specifically architected for application in nanoelectronic devices. We present a template-confined synthesis of metal chalcogenide (e.g., Ag2S, Cu2S) nanowires for mixed conductor-based nanoelectronics. First, the metal nanowire array was electroplated into pores of a porous alumina membrane. Anodic polarization was then used to transform the metal into the metal sulfide in aqueous hydrosulfide (HS−) solutions. The as-synthesized mixed conductors'' hetero-nanowire array was characterized by X-ray diffraction and electron microscopy. Electronic transport measurements show non-linear and reproducible electrical switching characteristics. The high and low resistance states can be reversibly changed by altering the polarity of the applied voltage between the bottom and top electrodes. The electrical-switching behavior is attributed to electric-field-induced accumulation and dissolution of metallic conducting pathways inside the mixed conductors'' nanowires. [Copyright &y& Elsevier]

Abstract: Patterned ferroelectric domains and domain selective etching of the patterned domains can provide ferroelectrics-based photonic crystals. In this paper, electron-beam has been applied to switch domains in LiNbO3 (LN) and LiTaO3 (LT) crystals. The complex dynamics of interaction of beam electrons with the crystals has been highlighted. Based on this research, an improved e-beam domain patterning technique utilizing resist covering is successfully applied to switch domains in a z-cut 1mol% MgO-doped stoichiometric LN at room temperature. [Copyright &y& Elsevier]

(a) Schematic illustration of the synthesis process of LSM, (b) top view of model structure. • The LSM are prepared by simple one-step topological reaction. • The LSM with two-dimensional structure has an ultrathin thickness of 20 nm. • The LSM has a large specific surface area and abundant pore sizes. • The LSM displays good specific capacity and cycling stability comparing with common Si material. The structure fracture of silicon electrodes due to the volume change during Si-Li alloying reactions greatly hinders their practical applications. Herein a layered Si material (LSM) was prepared by a simple one-step topological reaction and used as an effective LIBs anode. The layered structure has abundant gaps and pores to accelerate ion transportation. Microstructure measurements demonstrate the formation of an amorphous lithiation product but not Si-Li alloys. As a result, the LSM anode shows higher specific capacity and a much better cycling performance than common bulk Si anode. Thus, the LSM could be alternative high-performance Si anode in LIBs. [ABSTRACT FROM AUTHOR]

Graphene materials have attracted significant research interest as anodes in lithium-ion batteries (LIBs). However, their low volumetric capacity and high working voltage limit the energy density and thus hinder their practical applications. In this research, monolayer graphene and MoS 2 were prepared by controlled CVD growth processes. Graphene/MoS 2 alternately stacked structure (GMASS) was subsequently fabricated by alternately stacking graphene and MoS 2 monolayers layer by layer. When evaluated as an anode for LIB, GMASS demonstrates an obviously reduced working voltage compared to monolayer graphene electrodes (1.31 V vs. 1.46 V). And its volumetric capacity is much higher than that of an average graphite anode (1260 mAh cm−3 vs. 461 mAh cm−3). This fundamental research could promote the development of graphene/MoS 2 heterostructures for high-energy LIBs. Image 1 • Graphene/MoS 2 alternately stacked structure (GMASS) was fabricated. • GMASS demonstrates an obviously reduced working voltage. • GMASS shows a higher volumetric capacity comparing with graphite anode. [ABSTRACT FROM AUTHOR]

A general and straightforward strategy was developed for fabricating transition metal carbide (TMC)/carbon (C) core/shell nanospheres (NSs) by laser ablation of transition metals in acetone/ethanol liquid. Various TMC/C core/shell NSs such as TaC/C, NbC/C, HfC/C, and MoC/C core/shell NSs were successfully fabricated, highlighting the generality of this method. Crucially, this approach is green, facile, catalyst-free, and especially can be operated under ambient environments. Interestingly, all of the as-synthesized TMCs in the NS cores showed a cubic phase and structures similar to that of NaCl-type. The cores were further encapsulated by amorphous carbon shell with different thickness. As an example of the functional properties of these compound materials, the TaC/C core/shell NSs obtained were investigated as a supercapacitor electrode, which showed a large specific capacitance, excellent rate capability and remarkable cycling ability, revealing that the NSs could be used as new electrode materials for electrochemical energy storage. The photoluminescence of TaC/C core/shell NSs exhibited strong emission under the specific excitation wavelength at room temperature, showing potential biomedical applications due to the good biocompatibility of carbon shell. Besides, the basic physical and chemical reactions involved in the unique formation mechanism under highly nonequilibrium states induced by ultrafast laser ablation were discussed. [ABSTRACT FROM AUTHOR]

Abstract: A hard X-ray photoelectron spectroscopy (HX-PES) has been employed in order to investigate electrochemical polarization at carbon/amorphous tantalum oxide thin film hetero-interface. In situ HX-PES observation of Ta 4f and O 1s spectra has revealed parallel chemical shift of the core levels within the redox window width of 2.4eV, indicating Fermi level shifts due to the redox state modulation mediated by protonation and deprotonation under applied dc bias voltage. In addition to protons, oxide ions are suggested to take part in the redox state variation especially under a larger applied electric field. The results have been discussed in framework of solid state electrochemistry and Pourbaix-type E-pO diagram to indicate electrochemical stability domains of solid oxide systems is proposed. [Copyright &y& Elsevier]

[Display omitted] • In situ hard X-ray photoelectron spectroscopy was performed to investigate the origin of irreversibility in electrochromic Li x WO 3 thin films. • The appearance of irreversibility was observed in Li x WO 3 during operation. • Reversible/irreversible components generated during operation were distinguished and evaluated quantitatively. Three kinds of components are known in the insertion of Li+ into electrochromic WO 3 (Li x WO 3): (i) reversible Li+, (ii) irreversible Li 2 WO 4 formation and (iii) irreversible Li+ trapping. To develop Li x WO 3 -based electrochromic devices, in situ hard X-ray photoelectron spectroscopy (HAXPES), in situ Raman spectroscopy and electrochemical measurements were performed. In situ HAXPES can quantitatively distinguish (i) reversible Li+ and (iii) irreversible Li+ trapping as the variation in the oxidation state of the W ion whereas the electrochemical measurements can evaluate (i) reversible Li+ and the sum of (ii) irreversible Li 2 WO 4 formation and (iii) irreversible Li+ trapping. Furthermore, in situ Raman spectroscopy detected the enhancement of crystallinity due to Li+ insertion with high sensitivity. The combination of the in situ HAXPES and the electrochemical measurements enables the separation and quantitative evaluation of (i), (ii) and (iii). The inserted Li+ conversion ratios of (i) reversible Li+, (ii) irreversible Li 2 WO 4 formation and (iii) irreversible Li+ trapping to the entire inserted Li+ were clarified. (i.e. , 41.4 %, 50.9 %, and 7.7 %, respectively). [ABSTRACT FROM AUTHOR]

The domain switching at the nanoscale is studied at both −Z and +Z surfaces of a lithium niobate crystal. A remarkable difference between both surfaces is experimentally observed by scanning probe microscopy, and is theoretically analyzed by the structural property and the chemical bonding structure of the lithium niobate crystal. The domain switching at the −Z surface is much easier and more stable than that at the +Z surface, which makes lithium niobate crystals have potential applications in the future domain engineering, especially at the nanoscale level. [Copyright &y& Elsevier]