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Electrical switching of ferroelectric domains and subsequent domain wall motion promotes strong piezoelectric activity; however, light scatters at refractive index discontinuities such as those found at domain wall boundaries. Thus, simultaneously achieving large piezoelectric effect and high optical transmissivity is generally deemed infeasible. Here, it is demonstrated that the ferroelectric domains in perovskite Pb(In1/2 Nb1/2 )O3 Pb(Mg1/3 Nb2/3 )O3 -PbTiO3 domain-engineered crystals can be manipulated by electrical field and mechanical stress to reversibly and repeatably, with small hysteresis, transform the opaque poly-domain structure into a highly transparent mono-domain state. This control of optical properties can be achieved at very low electric fields (less than 1.5 kV cm-1 ) and is accompanied by a large (>10000 pm V-1 ) piezoelectric coefficient that is superior to that of linear state-of-the-art materials by a factor of three or more. The coexistence of tunable optical transmissivity and high piezoelectricity paves the way for a new class of photonic devices. This article is protected by copyright. All rights reserved.

Ba(Ga,Ta)0.05Ti0.90O3, a B-site dipole-like substituted material is investigated for structural phase transitions over the temperature range 30 to 900°C using x-ray diffraction. Rietveld refinement of the data suggests the material to be Pmm (cubic) from 200 to 900°C, P4/mmm (tetragonal) from 30 to 200°C with phases similar to those of BaTiO3 [12]. Average grain size determined using scanning electron microscopy is 650 nm. Measurements of dielectric properties from −50 to 120°C and over a frequency range of 10 Hz to 2 MHz show a relatively flat dielectric constant that is electric-field tunable indicating that Ba(Ga,Ta)0.05Ti0.90O3 is a reasonable candidate for frequency agile components.

Periodic density functional theory calculations elucidate carbon monoxide coverage effects on platinum and ruthenium surfaces. As expected the CO stretching frequencies increase with coverage. Unexpectedly, overlap population calculations show that increased stretching frequencies may not always correspond to stronger bonds. A theoretical framework is established based on a modified π-attraction σ-repulsion scheme. This phenomenological model directly relates the internal adsorbate bond strength to the net change of the carbon 2s and 2pxy contributions to the π- and σ-components, respectively. The variation of the metal–surface bond is examined by using the charges, polarizations, and electron densities of the adsorbate CO orbitals. For the systems studied here, the traditional frontier orbital model of the 5σ-donation/2π*-back-donation with the metal substrate bands is not always sufficient to explain the relative C–O and C–Metal bonds strengths.

The microwave ceramic Ba(Y,Sb)0.05Ti0.90O3, based upon random B-site dipole-like substitutions is structurally and electrically characterized over the temperature range −55°C to 120°C. X-ray diffraction information coupled together with scanning electron microscopy reveals that the material is single phase and has submicron grain sizes. Results show the tetragonal phase ranges from −30°C to 200°C, which is a broader temperature range than that of the parent material BaTiO3, 0°C to 120°C. The material Ba(Y,Sb)0.05Ti0.90O3 also has a diffuse relative high dielectric constant of about 10,000 that peaks at the orthorhombic-tetragonal structural phase transition around −30°C.

Periodic density functional theory calculations on carbon monoxide (CO) adsorbed atop on platinum–osmium binary alloys (PtOs2 and PtOs4) and the platinum–ruthenium–osmium tertiary alloy (PtRu2Os2) are used to elucidate the changes in the C–O and C–Pt bonds upon alloying Pt with Ru/Os atoms. As Pt is alloyed with Ru/Os atoms, the adsorbate internal bond (C–O bond) and the adsorbate–metal bond (C–Pt bond) strengthen following the substrate trends of PtOs4 > Pt > PtOs2 > PtRu2Os2 and Pt > PtOs4 > PtOs2 > PtRu2Os2, respectively. These trends are manifested by the corresponding C–O and C–Pt stretching frequencies and the CO adsorption energy variations. Here, we establish a theoretical framework based on the π-attraction σ-repulsion mechanism to explain the above results. This model correlates the charges, polarizations, and electron densities of the adsorbate CO orbitals, and the sp/d populations of the adsorbing Pt atom. For the systems studied here, the traditional theoretical model of 5σ-donation/2π*-back-...

The ensemble site requirements for the oxidative adsorption of methanol and ethanol on platinum based membrane electrode assemblies in operating liquid feed fuel cells were measured by CO stripping voltammetry. At 30 °C and 0.2 V vs reference hydrogen electrode (RHE), the COads coverage from directly dosed CO (COCO), methanol (COMeOH), and ethanol (COEtOH) are 94%, 49%, and 39%, respectively. At 50 °C the COMeOH and COEtOH approach equality. The ratio of COEtOH/COMeOH was simulated with assumed ensemble site requirements of 3 and 2 for ethanol and methanol respectively. Experimental and simulated ratios of 0.79 and 0.78 suggest that high surface area fuel cell Pt catalysts at 30 °C have adsorption properties similar to that of a Pt (100) surface. Potential dependent infrared spectroscopy of COMeOH and COEtOH from flash evaporated aqueous alcohols delivered to a 50 °C fuel cell show lower COEtOH relative to COMeOH with Stark tuning rates below 10 cm–1/V.

Nanocomposites of single-walled carbon nanotubes dispersed within polyvinylchloride have been obtained by using the solution path. High-power sonication was utilized to achieve a good dispersion of carbon nanotubes. Thermogravimetric analysis revealed that during the synthesis, processing, or thermal analysis of these nanocomposites the released chlorine is functionalizing the single-walled carbon nanotubes. The loading of polyvinylchloride by single-walled carbon nanotubes increases the glass transition temperature of the polymeric matrix, demonstrating the interactions between macromolecular chains and filler. Wide Angle X-Ray Scattering data suggested a drop of the crystallite size and of the degree of crystallinity as the concentration of single-walled carbon nanotubes is increased. The in situ chlorination and amorphization of nanotube during the synthesis (sonication step) is confirmed by Raman spectroscopy.

Negative compressibility is a sign of thermodynamic instability of open or non-equilibrium systems. In quantum materials consisting of multiple mutually coupled subsystems, the compressibility of one subsystem can be negative if it is countered by positive compressibility of the others. Manifestations of this effect have so far been limited to low-dimensional dilute electron systems. Here we present evidence from angle-resolved photoemission spectroscopy (ARPES) for negative electronic compressibility (NEC) in the quasi-three-dimensional (3D) spin-orbit correlated metal (Sr1-xLax)3Ir2O7. Increased electron filling accompanies an anomalous decrease of the chemical potential, as indicated by the overall movement of the deep valence bands. Such anomaly, suggestive of NEC, is shown to be primarily driven by the lowering in energy of the conduction band as the correlated bandgap reduces. Our finding points to a distinct pathway towards an uncharted territory of NEC featuring bulk correlated metals with unique potential for applications in low-power nanoelectronics and novel metamaterials., Advance online publication in Nature Materials; see the journal website for free download of Supplementary Information

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Composites of single walled carbon nanotube dispersed within polymeric matrices have been investigated by spectroscopic techniques (Raman and Wide Angle X-Ray Spectroscopy). Raman investigations included an in depth analysis of the radial breathing mode (for single wall carbon nanotubes) and a brief analysis of the lines originating from the polymeric matrix. Raman spectra were successfully simulated by computer assuming that the as recorded spectrum is a convolution of lines whose line shape is well described by a modified Breit-Wigner-Fano equation. The dependence of the position of the lines belonging to the radial breathing mode on the concentration of single walled carbon nanotube has been investigated, with emphasis on information pertinent to the stress transfer from the macromolecular matrix to the filler and to the coating of single walled carbon nanotube by polymeric chains. Complementary Wide Angle X-Ray Spectroscopy measurements provided information about the effect of the loading with single walled carbon nanotube on the crystal structure of the polymeric matrix. The research aims to a better understanding of the interactions between polymeric matrices and nanofillers.