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We report temperature-dependent transport and x-ray diffraction measurementsof the influence of Ti hole doping on the charge density wave (CDW) in1T-Ta(1-x)Ti(x)S(2). Confirming past studies, we find that even traceimpurities eliminate the low-temperature commensurate (C) phase in this system.Surprisingly, the magnitude of the in-plane component of the CDW wave vector inthe nearly commensurate (NC) phase does not change significantly with Ticoncentration, as might be expected from a changing Fermi surface volume.Instead, the angle of the CDW in the basal plane rotates, from 11.9 deg at x=0to 16.4 deg at x=0.12. Ti substitution also leads to an extended region ofcoexistence between incommensurate (IC) and NC phases, indicating heterogeneousnucleation near the transition. Finally, we explain a resistive anomalyoriginally observed by DiSalvo [F. J. DiSalvo, et al., Phys. Rev. B {\bf 12},2220 (1975)] as arising from pinning of the CDW on the crystal lattice. Ourstudy highlights the importance of commensuration effects in the NC phase,particularly at x ~ 0.08.

Ordered intermetallic nanoparticles are promising electrocatalysts with enhanced activity and durability for the oxygen-reduction reaction (ORR) in proton-exchange membrane fuel cells (PEMFCs). The ordered phase is generally identified based on the existence of superlattice ordering peaks in powder X-ray diffraction (PXRD). However, after employing a widely used postsynthesis annealing treatment, we have found that claims of "ordered" catalysts were possibly/likely mixed phases of ordered intermetallics and disordered solid solutions. Here, we employed in situ heating, synchrotron-based, X-ray diffraction to quantitatively investigate the impact of a variety of annealing conditions on the degree of ordering of large ensembles of Pt 3 Co nanoparticles. Monte Carlo simulations suggest that Pt 3 Co nanoparticles have a lower order-disorder phase transition (ODPT) temperature relative to the bulk counterpart. Furthermore, we employed microscopic-level in situ heating electron microscopy to directly visualize the morphological changes and the formation of both fully and partially ordered nanoparticles at the atomic scale. In general, a higher degree of ordering leads to more active and durable electrocatalysts. The annealed Pt 3 Co/C with an optimal degree of ordering exhibited significantly enhanced durability, relative to the disordered counterpart, in practical membrane electrode assembly (MEA) measurements. The results highlight the importance of understanding the annealing process to maximize the degree of ordering in intermetallics to optimize electrocatalytic activity., Competing Interests: The authors declare no conflict of interest.

Sodium-ion batteries have been considered as one of the most promising types of batteries, beyond lithium-ion batteries, for large-scale energy storage applications. However, their deployment hinges on the development of new anode materials, since it has been shown that many important anode materials employed in lithium ion batteries, such as graphite and silicon, are inadequate for sodium-ion batteries. We have simply prepared novel SnS/C nanocomposites through a top-down approach as anode materials for sodium-ion batteries. Their electrochemical performance has been significantly improved when compared to bare SnS, especially in terms of cycling stability and rate capabilities. SnS/C nanocomposites exhibit excellent capacity retention, at various current rates, and deliver capacities as high as 400 mA h g -1 even at the high current density of 800 mA g -1 (2C). Ex situ transmission electron microscopy, X-ray diffraction and operando X-ray absorption near edge structure studies have been performed in order to unravel the reaction mechanism of the SnS/C nanocomposites., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

A new technique for the parallel collection of X-ray reflectivity (XRR) data, compatible with monochromatic synchrotron radiation and flat substrates, is described and applied to the in situ observation of thin-film growth. The method employs a polycapillary X-ray optic to produce a converging fan of radiation, incident onto a sample surface, and an area detector to simultaneously collect the XRR signal over an angular range matching that of the incident fan. Factors determining the range and instrumental resolution of the technique in reciprocal space, in addition to the signal-to-background ratio, are described in detail. This particular implementation records ∼5° in 2θ and resolves Kiessig fringes from samples with layer thicknesses ranging from 3 to 76 nm. The value of this approach is illustrated by showing in situ XRR data obtained with 100 ms time resolution during the growth of epitaxial La 0.7 Sr 0.3 MnO 3 on SrTiO 3 by pulsed laser deposition at the Cornell High Energy Synchrotron Source (CHESS). Compared with prior methods for parallel XRR data collection, this is the first method that is both sample-independent and compatible with the highly collimated, monochromatic radiation typical of third-generation synchrotron sources. Further, this technique can be readily adapted for use with laboratory-based sources.

The miniaturization and integration of frequency-agile microwave circuits--relevant to electronically tunable filters, antennas, resonators and phase shifters--with microelectronics offers tantalizing device possibilities, yet requires thin films whose dielectric constant at gigahertz frequencies can be tuned by applying a quasi-static electric field. Appropriate systems such as BaxSr1-xTiO3 have a paraelectric-ferroelectric transition just below ambient temperature, providing high tunability. Unfortunately, such films suffer significant losses arising from defects. Recognizing that progress is stymied by dielectric loss, we start with a system with exceptionally low loss--Srn+1TinO3n+1 phases--in which (SrO)2 crystallographic shear planes provide an alternative to the formation of point defects for accommodating non-stoichiometry. Here we report the experimental realization of a highly tunable ground state arising from the emergence of a local ferroelectric instability in biaxially strained Srn+1TinO3n+1 phases with n ≥ 3 at frequencies up to 125 GHz. In contrast to traditional methods of modifying ferroelectrics-doping or strain-in this unique system an increase in the separation between the (SrO)2 planes, which can be achieved by changing n, bolsters the local ferroelectric instability. This new control parameter, n, can be exploited to achieve a figure of merit at room temperature that rivals all known tunable microwave dielectrics.