Effect of ionic radii on the Curie temperature in Ba1-x-ySrxCayTiO3 compounds

<p>A series of Ba_1-x-ySr_xCa_yTiO₃ compounds were prepared with varying average ionic radii and cation disorder on A-site. All samples showed typical ferroelectric behavior. A simple empirical equation correlated Curie temperature, <em>T_C</em>, with the values of ionic radii of A-site cations. This correlation was related to the distortion of TiO₆ octahedra observed during neutron diffraction studies. The equation was used for the selection of compounds with predetermined values of <em>T_C</em>. The effects of A-site ionic radii on the temperatures of phase transitions in Ba_1-x-ySr_xCa_yTiO₃ were discussed. </p

Tuning the electrocaloric enhancement near the morphotropic phase boundary in lead-free ceramics

This project was funded by EPSRC (EP/G060940/1 and EP/P505674/1) and the Grant Agency of the Slovak Academy of Sciences (2/0057/14)

Electrocaloric enhancement near the morphotropic phase boundary in lead-free NBT-KBT ceramics

The electrocaloric effects (ECEs) of the morphotropic phase boundary (MPB) composition 0.82(Na0.5Bi0.5)TiO3-0.18(K0.5Bi0.5)TiO3 (NBT-18KBT) are studied by direct measurements. The maximum ECE DTmax¼0.73K is measured at 160 C under 22 kV/cm. This corresponds to an ECE responsivity (DT/DE) of 0.33 10 6 K m/V, which is comparable with the best reported values for lead-free ceramics. A comparison between the direct and indirect ECE measurements shows significant discrepancies. The direct measurement of both positive and negative electrocaloric effect confirms the presence of numerous polar phases near the MPB of NBT-based materials and highlights their potential for solid-state cooling based on high field-induced entropy changes

Independent association between obstructive sleep apnea severity and glycated hemoglobin in adults without diabetes

OBJECTIVE: We tested the hypothesis of an independent cross-sectional association between obstructive sleep apnea (OSA) severity and glycated hemoglobin (HbA(1c)) in adults without known diabetes. RESEARCH DESIGN AND METHODS: HbA(1c) was measured in whole-blood samples from 2,139 patients undergoing nocturnal recording for suspected OSA. Participants with self-reported diabetes, use of diabetes medication, or HbA(1c) value ≥6.5% were excluded from this study. Our final sample size comprised 1,599 patients. RESULTS: A dose-response relationship was observed between apnea-hypopnea index (AHI) and the percentage of patients with HbA(1c) &gt;6.0%, ranging from 10.8% for AHI &lt;5 to 34.2% for AHI ≥50. After adjustment for age, sex, smoking habits, BMI, waist circumference, cardiovascular morbidity, daytime sleepiness, depression, insomnia, sleep duration, and study site, odds ratios (95% CIs) for HbA(1c) &gt;6.0% were 1 (reference), 1.40 (0.84-2.32), 1.80 (1.19-2.72), 2.02 (1.31-3.14), and 2.96 (1.58-5.54) for AHI values &lt;5, 5 to &lt;15, 15 to &lt;30, 30 to &lt;50, and ≥50, respectively. Increasing hypoxemia during sleep was also independently associated with the odds of HbA(1c) &gt;6.0%. CONCLUSIONS: Among adults without known diabetes, increasing OSA severity is independently associated with impaired glucose metabolism, as assessed by higher HbA(1c) values, which may expose them to higher risks of diabetes and cardiovascular disease

Association Between Severity of Obstructive Sleep Apnea and Blood Markers of Liver Injury

Obstructive sleep apnea (OSA) may contribute to the development of nonalcoholic fatty liver disease. We performed a multisite cross-sectional study to evaluate the association between the severity of OSA and blood markers of liver steatosis (using the hepatic steatosis index), cytolysis (based on alanine aminotransferase activity), and significant liver fibrosis (based on the FibroMeter [Echosens] nonalcoholic fatty liver disease score) in 1285 patients with suspected OSA in France. After adjusting for confounders including central obesity, the risk of liver steatosis increased with the severity of OSA (P for trend &lt; .0001) and sleep-related hypoxemia (P for trend &lt; .0003 for mean oxygen saturation). Decreasing mean oxygen saturation during sleep also was associated independently with a higher risk of liver cytolysis (P for trend &lt; .0048). Severe OSA conferred an approximate 2.5-fold increase in risk for significant liver fibrosis compared with patients without OSA, but the association between OSA severity and liver fibrosis was not maintained after adjusting for confounders

The PLATO 2.0 mission

PLATO 2.0 has recently been selected for ESA's M3 launch opportunity (2022/24). Providing accurate key planet parameters (radius, mass, density and age) in statistical numbers, it addresses fundamental questions such as: How do planetary systems form and evolve? Are there other systems with planets like ours, including potentially habitable planets? The PLATO 2.0 instrument consists of 34 small aperture telescopes (32 with 25 s readout cadence and 2 with 2.5 s candence) providing a wide field-of-view (2232 deg 2) and a large photometric magnitude range (4-16 mag). It focusses on bright (4-11 mag) stars in wide fields to detect and characterize planets down to Earth-size by photometric transits, whose masses can then be determined by ground-based radial-velocity follow-up measurements. Asteroseismology will be performed for these bright stars to obtain highly accurate stellar parameters, including masses and ages. The combination of bright targets and asteroseismology results in high accuracy for the bulk planet parameters: 2 %, 4-10 % and 10 % for planet radii, masses and ages, respectively. The planned baseline observing strategy includes two long pointings (2-3 years) to detect and bulk characterize planets reaching into the habitable zone (HZ) of solar-like stars and an additional step-and-stare phase to cover in total about 50 % of the sky. PLATO 2.0 will observe up to 1,000,000 stars and detect and characterize hundreds of small planets, and thousands of planets in the Neptune to gas giant regime out to the HZ. It will therefore provide the first large-scale catalogue of bulk characterized planets with accurate radii, masses, mean densities and ages. This catalogue will include terrestrial planets at intermediate orbital distances, where surface temperatures are moderate. Coverage of this parameter range with statistical numbers of bulk characterized planets is unique to PLATO 2.0. The PLATO 2.0 catalogue allows us to e.g.: - complete our knowledge of planet diversity for low-mass objects, - correlate the planet mean density-orbital distance distribution with predictions from planet formation theories,- constrain the influence of planet migration and scattering on the architecture of multiple systems, and - specify how planet and system parameters change with host star characteristics, such as type, metallicity and age. The catalogue will allow us to study planets and planetary systems at different evolutionary phases. It will further provide a census for small, low-mass planets. This will serve to identify objects which retained their primordial hydrogen atmosphere and in general the typical characteristics of planets in such low-mass, low-density range. Planets detected by PLATO 2.0 will orbit bright stars and many of them will be targets for future atmosphere spectroscopy exploring their atmosphere. Furthermore, the mission has the potential to detect exomoons, planetary rings, binary and Trojan planets. The planetary science possible with PLATO 2.0 is complemented by its impact on stellar and galactic science via asteroseismology as well as light curves of all kinds of variable stars, together with observations of stellar clusters of different ages. This will allow us to improve stellar models and study stellar activity. A large number of well-known ages from red giant stars will probe the structure and evolution of our Galaxy. Asteroseismic ages of bright stars for different phases of stellar evolution allow calibrating stellar age-rotation relationships. Together with the results of ESA's Gaia mission, the results of PLATO 2.0 will provide a huge legacy to planetary, stellar and galactic science

Upper limit of the electrocaloric peak in lead-free ferroelectric relaxor ceramics

The electrocaloric effect (ECE) of two compositions (x = 0.06 and 0.07) of (1 − x)(Na0.5Bi0.5)TiO3-xKNbO3 in the vicinity of the morphotropic phase boundary is studied by direct measurements. ΔTmax = 1.5 K is measured at 125 °C under 70 kV/cm for NBT-6KN while ΔTmax = 0.8 K is measured at 75 °C under 55 kV/cm for NBT-7KN. We show that the “shoulder,” TS, in the dielectric permittivity, marks the upper limit of the ECE peak under high applied electric fields. These results imply that the range of temperature with high ECE can be quickly identified for a given composition, which will significantly speed up the process of materials selection for ECE cooling

Optimisation of SrBi2(Nb,Ta)2O9 Aurivillius phase for lead-free electrocaloric cooling

© 2018 Elsevier Ltd The influence of different substitutional mechanisms on the electrocaloric effect of a lead-free SrBi2(Nb0.2Ta0.8)2O9Aurivillius phase was studied for application in electrocaloric cooling systems. The A-site substitution with barium efficiently reduced the temperature of maximum permittivity from about 300 °C to 100 °C. The A-site substitution induced phenomena that are typical of strong relaxor ferroelectrics such as significant broadening of the permittivity peak and an increase in its frequency dispersion and with a depolarization temperature below room temperature. These features directly influenced the electrocaloric effect. A direct measurement system, based on a modified-differential scanning calorimeter, was used to analyze the EC effect of the dense (Sr0.5Ba0.5)Bi2(Nb0.2Ta0.8)2O9ceramics. In accordance with the relaxor characteristics, the EC effect was found to increase continuously over a broad temperature range above the room temperature. This was attributed to the alignment of field induced polar nanodomains. Directions for optimization towards a high-performing EC ceramic were identified

Electrocaloric effect in lead-free Aurivillius relaxor ferroelectric ceramics

A lead-free Aurivillius phase based on SrBi2(Nb0.2Ta0.8)2O9 was studied for potential application in electrocaloric (EC) cooling systems. Doping with praseodymium proved to be effective in reducing the temperature of maximum permittivity from about 300°C to 80°C. The praseodymium doping also led to a broadening of the permittivity peak and an increase in its frequency dispersion, which are typical features of strong relaxor ferroelectrics. A direct measurement system, based on a modified-differential scanning calorimeter, was used to analyze the EC effect of dense SrBi1.85Pr0.15(Nb0.2Ta0.8)2O9 ceramics. Unlike the trend observed in classic ferroelectrics, the EC effect in this relaxor ferroelectric was found to increase significantly over a broad temperature range well above the temperature of depolarization. This was attributed to the contribution of the polar nanodomain alignment that is induced by the external electric field. Directions for further optimization of this lead-free relaxor towards a high-performing EC material were identified. A comparison between the direct and indirect EC measurements showed significant discrepancies, not only in a magnitude but also in the trend. These discrepancies were attributed to the non-ergodic relaxor state of the Aurivillius phase, which cannot be described with Maxwell equations. For materials displaying such characteristics indirect methods to predict EC effect may be unreliable requiring that the EC effect be measured by a direct EC characterization technique