Spontaneous and induced ferroelectricity in the BiFe1−xScxO3 perovskite ceramics

High-pressure synthesis method allows obtaining single-phase perovskite BiFe1-xScxO3 ceramics in the entire concentration range. As-prepared compositions with x from 0.30 to 0.55 have the antipolar orthorhombic Pnma structure but can be irreversible converted into the polar rhombohedral R3c or the polar orthorhombic Ima2 phase via annealing at ambient pressure. Microstructure defects and large conductivity of the high-pressure-synthesized ceramics make it difficult to study and even verify their ferroelectric properties. These obstacles can be overcome using piezoresponse force microscopy (PFM) addressing ferroelectric behavior inside single grains. Herein, the PFM study of the BiFe1-xScxO3 ceramics (0.30 ≤ x ≤ 0.50) is reported. The annealed samples show a strong PFM contrast. Switching of domain polarity by an electric field confirms the ferroelectric nature of these samples. The as-prepared BiFe0.5Sc0.5O3 ceramics demonstrate no piezoresponse in accordance with the antipolar character of the Pnma phase. However, application of a strong enough electric field induces irreversible transition to the ferroelectric state. The as-prepared BiFe0.7Sc0.3O3 ceramics show coexistence of ferroelectric and antiferroelectric grains without poling. It is assumed that mechanical stress caused by the sample polishing can be also a driving force of phase transformation in these materials alongside temperature and external electric field.publishe

The ACTN3 R577X Polymorphism across Three Groups of Elite Male European Athletes

The ACTN3 R577X polymorphism (rs1815739) is a strong candidate to influence elite athletic performance. Yet, controversy exists in the literature owing to between-studies differences in the ethnic background and sample size of the cohorts, the latter being usually low, which makes comparisons difficult. In this case:control genetic study we determined the association between elite athletic status and the ACTN3 R577X polymorphism within three cohorts of European Caucasian men, i.e. Spanish, Polish and Russian [633 cases (278 elite endurance and 355 power athletes), and 808 non-athletic controls]. The odds ratio (OR) of a power athlete harbouring the XX versus the RR genotype compared with sedentary controls was 0.54 [95% confidence interval (CI): 0.34–0.48; P = 0.006]. We also observed that the OR of an endurance athlete having the XX versus the RR genotype compared with power athletes was 1.88 (95%CI: 1.07–3.31; P = 0.028). In endurance athletes, the OR of a “world-class” competitor having the XX genotype versus the RR+RX genotype was 3.74 (95%CI: 1.08–12.94; P = 0.038) compared with those of a lower (“national”) competition level. No association (P>0.1) was noted between the ACTN3 R577X polymorphism and competition level (world-class versus national-level) in power athletes. Our data provide comprehensive support for the influence of the ACTN3 R577X polymorphism on elite athletic performance

Evidence for CO Disproportionation over Ceria during Oxygen Storage Capacity Measurements: an in Situ Raman Spectroscopic Investigation

The interaction of CO with ceria under conditions typical for oxygen storage capacity (OSC) measurements of three way catalysts (TWC) has been investigated by in situ Raman spectroscopy. It has been shown that CO disproportionates over ceria at 623 K to deposit disordered carbon nano-crystallites, with calculated average crystal size of less than 20 Å. Exposure of the carbonized ceria to gaseous O2 at room temperature resulted in the disappearance of the bands attributed to the carbon in Raman spectra, accompanied by the emerging of bands of surface formates, carbonates, and adsorbed peroxide species. Even though the kinetics of the ceria-catalyzed CO disproportionation reaction has yet to be measured, the present investigation suggests that the generally accepted procedure for OSC measurements of TWCs results in an OSC overestimation and, hence, needs to be reconsidered

Evidence for CO Disproportionation over Ceria during Oxygen Storage Capacity Measurements: an in Situ Raman Spectroscopic Investigation

The interaction of CO with ceria under conditions typical for oxygen storage capacity (OSC) measurements of three way catalysts (TWC) has been investigated by in situ Raman spectroscopy. It has been shown that CO disproportionates over ceria at 623 K to deposit disordered carbon nano-crystallites, with calculated average crystal size of less than 20 Å. Exposure of the carbonized ceria to gaseous O2 at room temperature resulted in the disappearance of the bands attributed to the carbon in Raman spectra, accompanied by the emerging of bands of surface formates, carbonates, and adsorbed peroxide species. Even though the kinetics of the ceria-catalyzed CO disproportionation reaction has yet to be measured, the present investigation suggests that the generally accepted procedure for OSC measurements of TWCs results in an OSC overestimation and, hence, needs to be reconsidered

Carbon Monoxide Disproportionation over Ceria-Containing Materials

The disproportionation of CO catalyzed by ceria is demonstrated in this Raman spectroscopic investigation of the interaction of CO with ZrO2, Pd/ZrO2, Ce0.75Zr0.25O2, and Pd/Ce0.75Zr0.25O2Методом спектроскопии комбинационного рассеяния исследовано взаимодействие СО с ZrO2, Pd/ZrO2, Ce0.75Zr0.25O2, и Pd/Ce0.75Zr0.25O2 катализаторами дожигания выхлопных газов. Показана возможность диспропорционирования моноксида углерода в условиях измерения буферной ёмкости каталитических материалов по кислороду

High Structure Sensitivity of Vapor-Phase Furfural Decarbonylation/Hydrogenation Reaction Network as a Function of Size and Shape of Pt Nanoparticles

Vapor-phase transformations of furfural in H 2 over a series of Pt nanoparticles (NPs) with various particle sizes (1.5-7.1 nm size range) and shapes (rounded, cubes, octahedra) encapsulated in poly(vinylpyrrolidone) (PVP) and dispersed on MCF-17 mesoporous silica were investigated at ambient pressure in the 443-513 K temperature range. Furan and furfuryl alcohol (FFA) were two primary products as a result of furfural decarbonylation and hydrogenation reactions, respectively. Under conditions of the study both reactions exhibited structure sensitivity evidenced by changes in product selectivities, turnover rates (TORs), and apparent activation energies (E A's) with Pt particle size and shape. For instance, upon an increase in Pt particle size from 1.5 to 7.1 nm, the selectivity toward FFA increases from 1% to 66%, the TOR of FFA production increases from 1 ?? 10 -3 s -1 to 7.6 ?? 10 -2 s -1, and E A decreases from 104 kJ mol -1 to 15 kJ mol -1 (9.3 kPa furfural, 93 kPa H 2, 473 K). Conversely, under the same experimental conditions the decarbonylation reaction path is enhanced over smaller nanoparticles. The smallest NPs (1.5 nm) produced the highest selectivity (96%) and highest TOR values (8.8 ?? 10 -2 s -1) toward furan formation. The E A values for decarbonylation (???62 kJ mol -1) was Pt particle size independent. Furan was further converted to propylene via a decarbonylation reaction, but also to dihydrofuran, tetrahydrofuran, and n-butanol in secondary reactions. Furfuryl alcohol was converted to mostly to 2-methylfuran. © 2012 American Chemical Society.close383

Hydrogenation of benzene and toluene over size controlled Pt/SBA-15 catalysts: Elucidation of the Pt particle size effect on reaction kinetics

Vapor-phase hydrogenation of benzene and toluene over a size-dependent (1.5–5.2 nm) series of Pt nanoparticles (NPs) encapsulated in polyvinylpyrrolidone (PVP) or polyamidoamine (PAMAM) dendrimer and supported in SBA-15 mesoporous silica was investigated at ambient pressure between 343 K and 398 K. Under these conditions, both reactions exhibit a moderate structure sensitivity evidenced by changes in their turnover rate (TOR), apparent activation energy (EA), pre-exponential factor ln(r0), and deactivation rate parameters with Pt particle size. For instance, the 2.4–3.1 nm Pt NPs showed the highest TOR for both reactions as compared to NPs of either smaller or larger sizes. Also, the EA and ln(r0) factor values were larger for smaller Pt particle sizes, and the rates of catalyst deactivation were more pronounced for catalysts with larger Pt particle sizes. However, the reaction orders on H2 and hydrocarbon were independent of particle size