Shenhui Lei

Phase transformation (cubic to rhombohedral): the effect on the NO2 sensing performance of Zn-doped flower-like In2O3 structures

Cubic In2O3 (bcc-In2O3) was transformed into a mixture of bcc-In2O3 and rhombohedral In2O3 (rh-In2O3) by Zn doping. The Zn-doped flower-like In2O3 structures consisted of many thin sheets with a length of 0.4–1 μm, and cubes with a length of 200 nm, while the size of the microflowers was 1–3.5 μm. The Zn doping concentration significantly affected the phase transformation and the overall morphology of In2O3. Furthermore, the analysis of N2 adsorption–desorption measurements showed that the Zn-doped flower-like In2O3 structures (sample S5) adsorbed the largest amount of N2 and had the biggest surface area (46.41 m2 g−1), which contributed to an improvement in gas sensing performance. Finally, sensors based on the mixture of bcc- and rh-In2O3 structures exhibited a much higher response to NO2 than the pure bcc-In2O3 (sample S1), and the Zn-doped flower-like In2O3 structures (sample S5) exhibited the highest response of 27.4 ± 2.5 for 5 ppm NO2. Thus, the gas sensing performance of In2O3 was enhanced significantly by the phase transformation.

Pt-decorated zinc oxide nanorod arrays with graphitic carbon nitride nanosheets for highly efficient dual-functional gas sensing.

In this work, well-aligned ZnO nanorods were grown on the substrate of exfoliated g-C3N4 nanosheets via a microwave-assisted hydrothermal synthesis, and then Pt/ZnO/g-C3N4 nanostructures were obtained after the deposition of Pt nanoparticles. The growth of vertically ordered ZnO nanorods was occurred on g-C3N4 nanosheets through the bonding interaction between Zn and N atoms, which was confirmed by XPS, FT-IR data and molecular orbital theory. The Pt/ZnO/g-C3N4 nanostructures sensor exhibited the remarkable sensitivity, selectivity, and fast response/recovery time for air pollutants of ethanol and NO2. The application of Pt/ZnO/g-C3N4 nanostructures could be used as a dual-functional gas sensor through the controlled working temperature. Besides, the Pt/ZnO/g-C3N4 nanostructures sensor could be applied to the repeating detection of ethanol and NO2 in the natural environment. The synergistic effect and improved the separation of electron-hole pairs in Pt/ZnO/g-C3N4 nanostructures had been verified for the gas sensing mechanism. Additionally, Pt/ZnO/g-C3N4 nanostructures revealed the excellent charge carriers transport properties in electrochemical impedance spectroscopy (EIS), such as the longer electron lifetime (τn), higher electron diffusion coefficient (Dn) and bigger effective diffusion length (Ln), which also played an important role for Pt/ZnO/g-C3N4 nanostructures with striking gas sensing activities.

Novel sintering and band gap engineering of ZnTiO3 ceramics with excellent microwave dielectric properties

Pure phase ZnTiO3 ceramics were successfully synthesized for the first time by a solid state reaction method. The synthesis temperature was higher than the phase transition temperature, wherein the ZnO nanoparticles acted as inhibitors to prevent the formation of the secondary phase, Zn2TiO4, which was inevitable by conventional preparation methods. As the small nano-ZnO regions dispersed in the ceramic grains, the bulk diffusion of Ti ions, formation of nucleation centers and migration of phase boundaries were largely suppressed, indicating that nano-ZnO was desirable for stabilizing the ZnTiO3 phase above the phase transition temperature. The R (no. 148) space groups of the single phase were determined by X-ray diffraction Rietveld analysis. X-ray photoelectron spectroscopy and photoluminescence emission spectroscopy were also carried out to investigate the electronic microstructure of the obtained ZnTiO3 phase. Finally, excellent microwave dielectric properties were achieved (er ∼ 31.5, Q × f ∼ 59 800 GHz and τf ∼ 1.2 ppm °C−1) with a high sintering temperature (900–950 °C). Moreover, given its good chemical compatibility with the Ag electrode and the merits of easy scale-up, high-efficiency, low-cost and environmentally benign synthesis, ZnTiO3 is a promising candidate for LTCC applications. This work paves a great way towards practical applications.

Unusual devisable high-performance perovskite materials obtained by engineering in twins, domains, and antiphase boundaries

With the widespread application, engineering of microstructures, domains, twins, and antiphase boundaries (APBs) is attracting significant attention. However, the origin of the domains, especially in the paraelectric phase, as well as the mechanism of variation in twins or domains and their relationship are still not clear. Generally, these structures are recognized as one of the key origins of intrinsic loss. Our studies, however, reveal that the formation of twins is closely related to the asymmetry of the crystal structure. With the introduction of a lattice blockage-trigonal NdAlO3 phase, the increase in the symmetry of the CaTiO3 tetragonal phase results in a transformation from the (110)-oriented twins to the (111)-oriented twins. Then, it forms a new ordered structure. With the help of peak-differentiation and imitation of the Raman spectra, the A-site in the perovskite structure is found to be a dominant factor in lattice energy and performance. By designing an A-site displacement, i.e., Sr2+ or Ba2+ substitution into Ca2+, we created a controllable structure of twins by symmetry regulation and APBs by introducing ferroelectric spontaneous polarization. Via selected area electron diffraction patterns (SAED) and variable temperature electric field piezoresponse force microscopy (PFM) images, we found that 180° and 90° domains could coexist in the grains of xCaTiO3–(1 − x)NdAlO3 ceramics. Interestingly, the 90° domains and twin boundaries (TB) play more important roles in the anisotropic resistance to the electron/hole transfer. Our studies prove that the defect engineering can realize a controllable enhanced dielectric performance by defect regulation within the host lattice. These may pave a possible way for the design of the microstructure of the defects to achieve better predictable performances of the materials.