No abstract

High-pressure behavior of carbon supported Pt nanoparticles (Pt/C) with an average particle size of 10.6 nm was investigated by in situ high-pressure synchrotron radiation x-ray diffraction up to 14 GPa at ambient temperature. Our results show that the compressibility of Pt/C nanoparticles decreases substantially as the particle size decreases. An interpretation based upon the available mechanisms of structural compliance in nanoscale vs bulk materials was proposed.

Supported PtCu/C electrocatalysts containing core–shell bimetallic PtCu nanoparticles were synthesized by sequential chemical reduction of Cu2+ and Pt­(IV) in a carbon suspension, prepared on the basis of ethylene glycol–water solvent, and then treated at different temperatures in the range from 250 to 350 °C. The structural characterization of “as-prepared” PtCu nanoparticles and of those obtained after the thermal treatments was performed by transmission electron microscopy, X-ray diffraction, and Pt L3- and Cu K-edge extended X-ray absorption fine structure spectroscopy. The atomic cluster models of PtCu nanoparticles before and after the thermal treatment, reflecting the character of the components’ distribution, were generated. The electrochemical performance of the obtained PtCu/C electrocatalysts in oxygen reduction reaction was studied by cycling and linear voltammetry.

No abstract

In the present work, the effect of grain size distribution on the diffraction profile shape is inspected via analysis of the mutual ratio of Lorentz and Gauss components in pseudo-Voigt function which is used for simulating X-ray profiles of nanoparticles. As established from the plotted dependences, the error in the average Pt nanoparticles size determination reaches 56% and the discrepancy between calculated Pt nanoparticle surface areas attains 60%. Furthermore, the determination error becomes greater with increasing the Lorentz contribution to pseudo-Voigt function, or, in fact, with enlarging particle size distribution. The empirically found electrochemical surface area of Pt/C electrocatalyst is compared with that evaluated from XRD data using the Scherrer formula and particle size distribution data analysis.

No abstract

The crystal structure and lattice dynamics of quantum paraelectric BaxSr1−xTiO3 (x = 0, 0.01, 0.02) solid solutions are studied using X‐ray diffraction (XRD), Raman and terahertz‐infrared (THz‐IR) spectroscopies in a temperature range of 4–300 K. XRD and Raman spectroscopy reveal the cubic‐to‐tetragonal nonpolar structural phase transition at about 100 K. At the same time, Raman spectra manifest the presence of polar modes, TO2 and TO4, normally prohibited in paraelectric phase. Emergence of these modes indicates the appearance of the polar nanoregions in a broad temperature range. The modes become more intensive at low temperatures, and temperature dependence of their intensities on cooling reveals the kink‐like change of the slope from flat to steep, indicating on activation of polar nanoregions. The transmission THz‐IR spectra show that squared frequency of the polar TO1 soft mode, responsible for ferroelectric transition, follows Cochran's behavior at high temperatures. However, at low temperatures, it doesn't vanish at extrapolated Curie temperature but saturates, demonstrating the plateau feature below 20 K. This behavior, coherent with known saturation of the dielectric constant, indicates that transition to ferroelectric phase in BaxSr1−xTiO3 is suppressed by quantum fluctuations and the system stays in quantum paraelectric state at very low temperatures.

Interest in the development of state-of-the-art methods for synthesis of Pt nanoparticles is dictated by both unique properties of platinum itself and the wide range of platinum nanoparticles applications. Platinum acetylacetonate and platinum nanoparticles produced by the thermal decomposition of Pt(acac) 2 are studied via in situ X-ray diffraction and Raman spectroscopy, thermal gravimetry, scanning (SEM), and transmission electronic microscopy (TEM). The experiments are made at heating rates of 1 and 5 K min À1 . A comparative analysis of SEM, TEM, and XRD data highlights the formation of coarse Pt particles with sizes of %60-160 nm, which are composed of nanoparticles with dimensions of 1.9 and 4.1 nm for 1 K min À1 -and 5 K min À1 -heating rates, respectively. The desirable average size of nanoparticles upon their synthesis can thus be achieved by a simple tuning of the heating rate of acetylacetate thermal decomposition. The present results open up the possibility to use a trivial non-isothermal thermal decomposition method in the synthesis of both supported and unsupported nanoparticles of predetermined size for other chemical elements such as Pd, Ni, Co, etc. from their acetylacetonates.