Anomalous thermoelectric effects of ZrTe5_{5} in and beyond the quantum limit

Thermoelectric effects are more sensitive and promising probes to topological properties of emergent materials, but much less addressed compared to other physical properties. Zirconium pentatelluride (ZrTe$_{5}$) has inspired active investigations recently because of its multiple topological nature. We study the thermoelectric effects of ZrTe$_{5}$ in a magnetic field and find several anomalous behaviors. The Nernst response has a steplike profile near zero field when the charge carriers are electrons only, suggesting the anomalous Nernst effect arising from a nontrivial profile of Berry curvature. Both the thermopower and Nernst signal exhibit exotic peaks in the strong-field quantum limit. At higher magnetic fields, the Nernst signal has a sign reversal at a critical field where the thermopower approaches to zero. We propose that these anomalous behaviors can be attributed to the Landau index inversion, which is resulted from the competition of the $\sqrt{B}$ dependence of the Dirac-type Landau bands and linear-$B$ dependence of the Zeeman energy ($B$ is the magnetic field). Our understanding to the anomalous thermoelectric properties in ZrTe$_{5}$ opens a new avenue for exploring Dirac physics in topological materials.Comment: 6 pages, 4 figure

Promotional effect of H2O introduction on the NH3-SCR activity of the gas-phase sulfated CeO2 catalyst by organic CS2+COS : Influence of H2O concentration

Herein, as an indispensable key reactant for the hydrolysis of organic sulfur, H2O was firstly introduced to optimize the NH3-SCR activity of CeO2 by providing the adsorption and reaction spots of catalysis for organic CS2+COS during the low-temperature gas-phase sulfation. The results demonstrate that the introduction of 0.33 vol% H2O is beneficial to enhance the interaction between organic CS2+COS and cube fluorite CeO2, which not only increases the concentrations of Ce3+ ions, chemisorbed oxygen (Oβ) and oxygen vacancies on CeO2-CS2+COS surface, but also effectively enhances the redox cycle of Ce4+/Ce3+ ion pairs and the medium-strong acid sites of catalyst. These all help enhance the promotional effect of organic sulfur low-temperature gas-phase sulfation on the NH3-SCR activity of CeO2 and further improve NOx reduction over the CeO2-CS2+COS catalyst. However, the introduction of 5.0 vol% H2O shows a certain inhibitory effect due to the competitive adsorption of excess water and CS2+COS on the cube fluorite CeO2 surface, which weakens their interaction during the low-temperature gas-phase sulfation, thereby decreases the promotional effect of low concentration water introduction on the NH3-SCR activity of the CeO2-CS2+COS catalyst. Therefore, the results of this research provide a scientific reference for developing the NH3-SCR CeO2-based catalyst in practical applications

Influence of organic sulfur gas-phase sulfation on the NH3-SCR activity of CeO2 catalyst : The competitive adsorption and conversion of CS2 and COS at a low hydrolysis temperature

in this study, a simplified approach is proposed to realize the gas-phase sulfation of CS2 or/and COS at the hydrolysis temperature for further facilitating the NH3-SCR activity of CeO2 in diverse conditions. A low-temperature oxidation conversion process for the adsorbed CS2 or COS on cubic fluorite CeO2 surface is developed. It is found that the gas-phase sulfation of organic CS2 or/and COS at 50 °C enhances the mobility of lattice oxygen of cubic fluorite CeO2 and the concentration of oxygen defects for the sulfated CeO2 catalyst, but the kinds of organic COS/CS2 can regulate the formed types and quality of sulfur-containing species on the catalyst surfaces during the gas-phase sulfation. and the formed sulfates under the gas-phase sulfation of CS2 are more active than those of COS, and CeO2-CS2-50 °C-3 h presents the best mobility of lattice oxygen, the largest concentration of adsorbed oxygen and the best NH3-SCR activity. Furthermore, the competitive adsorption and conversion of CS2 and COS is disadvantageous for the formation of oxygen vacancies on the catalyst surfaces compared to single CS2 or COS. However, the long-time durability testing coupling re-cycle experiments can optimize the oxygen vacancy defects and increase the concentration of chemisorbed oxygen of the sulfated CeO2-CS2 + COS-50 °C-24 h catalyst via optimizing the oxidization of sulfur element to sulfur oxides or/and sulfates, thereby improves its NH3-SCR activity. And the sulfated CeO2 catalyst by the gas-phase sulfation of organic COS + CS2 presents a good stability for NH3-SCR reaction. This study specifies a novel approach to simplify the gas-phase sulfation process of CeO2 catalyst, which is valuable in promotion of the NH3-SCR activity of CeO2 and reduction of cost in experimental procedures

Development of a carbon nanotube based microfocus x-ray tube with single focusing electrode

We report a detailed study on the design of carbon nanotube based microfocus x-ray tube with one electrostatic focusing electrode. Based on the electron optics simulations, such parameters as geometrical distances and applied voltages among all the electrodes are considered, respectively, in relation to the size of x-ray focal spot. The stability of the x-ray focal spot size is also examined with respect to the variation of gate and anode voltages. Experimental results that agree well with the simulated data are also provided to corroborate the design method. We also discuss the operating stability and limitations when designing a carbon nanotube based microfocus x-ray tube with only one electrostatic focusing electrode. The designed x-ray tube with an isotropic focal spot sees wide applications in in vivo medical imaging studies