Effects of aging on ScSZ/LSCrF dual-phase oxygen transport membrane for syngas production

A dual-phase composite material comprised of scandia-stabilized zirconia (ScSZ) and doped lanthanum chromite (La,Sr)(Cr,Fe)O3-δ (LSCrF) was investigated in this work as a potential oxygen transport membrane material in the production of synthesis gas. The main focus of this work was to examine the effects of exposure to three aging environments (air, 4% H2-96% N2, 5% H2-95% CO2) for two durations (300 hours, 1000 hours) on the oxygen transport kinetics and surface chemistry of ScSZ/LSCrF. Determination of the oxygen ion conductivity via Electrochemical Impedance Spectroscopy of single-phase ScSZ showed a decrease in the activation energy above 600˚C corresponding to a change in crystal phase at this temperature. Determination of the oxygen transport kinetics in dry oxygen (18O2) atmosphere on single-phase ScSZ via Isotopic Exchange Depth Profiling combined with Secondary Ion Mass Spectrometry showed the material exhibited an oxygen self-diffusion coefficient on the order of 10-8 cm2 s-1 at 700˚C for 30 minutes but required the application of a catalytic layer to boost oxygen surface exchange to detectable levels. Examinations of the surface chemistry of polished single-phase ScSZ and LSCrF via Low Energy Ion Scattering and X-ray Photoelectron Spectroscopy showed minimal differences to the ideal bulk stoichiometry. Determination of the crystal structure of dual-phase ScSZ/LSCrF via X-ray diffraction showed secondary phase formation in the samples after 300 hours of aging in air and 5%H2-95%CO2, and in all samples after 1000 hours of aging. Oxygen transport kinetics of dual-phase ScSZ/LSCrF under dry oxygen showed minor differences in D* and k* after exposure to the aging environments for 300 hours when compared to the unaged material, but an increase in surface exchange kinetics was observed for the materials aged in reducing conditions for 1000 hours. D* and k* in dual-phase ScSZ/LSCrF were on the order of 10-8 cm2 s-1 and 10-8 cm s-1 respectively before and after aging up to 1000 hours. Oxygen surface exchange kinetics are increased by about one order of magnitude when performed in water vapor (H218O) over dry oxygen. Examinations of the surface chemistry of as-prepared dual-phase ScSZ/LSCrF showed Cr depletion on the outer atomic surface of all samples, in addition to elevated surface fraction of Zr within ~10 nm of the sample surface.Open Acces

Preliminary Tc calculations for iron-based superconductivity in NaFeAs, LiFeAs, FeSe and nanostructured FeSe/SrTiO3 Superconductors

Many theoretical models of iron-based superconductors have been proposed but Tc calculations based on the models are usually missing. We have chosen two models of iron-based superconductors in the literature and then compute the Tc values accordingly: Recently two models have been announced which suggest that superconducting electron concentration involved in the pairing mechanism of iron-based superconductors may have been underestimated, and that the antiferromagnetism and the induced xy potential may even have a dramatic amplification effect on electron-phonon coupling. We use bulk FeSe, LiFeAs and NaFeAs data to calculate the Tc based on these models and test if the combined model can predict the superconducting transition temperature (Tc) of the nanostructured FeSe monolayer well. To substantiate the recently announced xy potential in the literature, we create a two-channel model to separately superimpose the dynamics of the electron in the upper and lower tetrahedral plane. The results of our two-channel model support the literature data. Our computational model takes into account this amplifying effect of antiferromagnetism and the correction of the electron-phonon scattering matrix together with the abnormal soft out-of-plane lattice vibration of the layered structure, which allows us to calculate theoretical Tc values of LiFeAs, NaFeAs and FeSe as a function of pressure that correspond reasonably well to the experimental values. More importantly, by taking into account the interfacial effect between an FeSe monolayer and its SrTiO3 substrate as an additional gain factor, our calculated Tc value is up to 91 K high, and provides evidence that the strong Tc enhancement recently observed in such monolayers with Tc reaching 100 K may be contributed from the electrons within the ARPES range.Comment: arXiv admin note: text overlap with arXiv:1905.1342

Decoding 122-Type Iron-Based Superconductors: A Comprehensive Simulation of Phase Diagrams and Transition Temperatures

Iron-based superconductors, a cornerstone of low-temperature physics, have been the subject of numerous theoretical models aimed at deciphering their complex behavior. In this study, we present a comprehensive approach that amalgamates several existing models and incorporates experimental data to simulate the superconducting phase diagrams of the principal 122-type iron-based compounds. Our model considers a multitude of factors including the momentum dependence of the superconducting gap, spin-orbital coupling, antiferromagnetism, spin density wave, induced XY potential on the tetrahedral structure, and electron-phonon coupling. We have refined the electron-phonon scattering matrix using experimental angle-resolved photoemission spectroscopy (ARPES) data, ensuring that all electrons pertinent to iron-based superconductivity are accounted for. This innovative approach allows us to calculate theoretical critical temperature Tc values for Ba1-xKxFe2As2, CaFe2As2 and SrFe2As2 as functions of pressure. These calculated values exhibit remarkable agreement with experimental findings. Furthermore, our model predicts that MgFe2As2 remains non-superconducting irrespective of the applied pressure. Given that 122-type superconductivity at low pressure or low doping concentration has been experimentally validated, our combined model serves as a powerful predictive tool for generating superconducting phase diagrams at high pressure. This study underscores that the high transition temperatures and the precise doping and pressure dependence of iron-based superconductors are intrinsically linked to an intertwined mechanism involving a strong interplay between structural, magnetic and electronic degrees of freedom

Edge effect and significant increase of the superconducting transition onset temperature of 2D superconductors in flat and curved geometries

In this paper, we present a simple method to model the curvature activated phonon softening in a 2D superconducting layer. The superconducting transition temperature Tc in the case of a 2D rectangular sheet, a hollow cylinder and a hollow sphere of one coherence length thickness is calculated by the quantum mechanical electron-phonon scattering matrix, and a series of collective lattice vibrations in the surface state. We will show that being extremely thin in a flat rectangular shape is not enough to significantly enhance the Tc through phonon softening. However, if a curvature is added, Tc can be strongly enhanced. The increase in Tc with respect to the bulk is greatest in a hollow sphere, intermediate in a hollow cylinder and weakest for the rectangular sheet, when systems of identical length scale are considered. In addition, we find that the edge effect of such a 2D sheet has a strong broadening effect on Tc in addition to the effect of order parameter phase fluctuations.Comment: Physica C, in pres

Perceived Attributes of Music Teaching Effectiveness Among Kindergarten Teachers: Role of Personality

: Musical activity has been found to be beneficial to young children’s all-round development in kindergartens. The purpose of this study was to investigate the relationship between kindergarten teachers’ perceived attributes of music teaching effectiveness and personality. Eighty-eight in-service kindergarten teachers rated themselves using a set of Attributes of Music Teaching Effectiveness (AMTE) and the sensing-intuitive dimension of the Myers Briggs Type Indicator. Results showed that 75% (66 of 88) and 25% (22 of 88) of the teachers were sensing types and intuitive types, respectively. The former prefers a directive approach in music teaching to children, whereas the latter prefers a non-directive approach. While teachers’ personalities and work experience significantly predicted music teaching effectiveness, intuitive teachers rated themselves higher than did sensing teachers on the AMTE. Furthermore, the teachers of both personality types varied in their ratings of the importance of most effective attributes. Implications of these findings in relation to job allocation and professional development in effective music teaching for kindergarten teachers are discussed

Mainland Chinese Tourists’ Expectations, Perceived Performance of and Satisfaction towards Shopping Malls in Hong Kong

Tourists from mainland China constitute one of the world's biggest and fastest-growing travel markets. The Hong Kong Tourism Board expects the frequency of the mainland Chinese tourists to grow steadily. One of the beneficiaries of this phenomenon is Hong Kong’s shopping malls. However, understanding of tourists from mainland China’s expectations from, perceived performance of and satisfaction with the shopping malls’ attributes in Hong Kong is inadequate. This study intends to fill this important gap. A survey questionnaire was employed for data collection. The main results reveal the mainland Chinese tourists’ levels of satisfaction, indifference and dissatisfaction as well as the relationship between shopping malls’ attributes and customer satisfaction