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This paper reports a facile two-step synthesis route for the preparation of flower-like ZnO/α-Fe 2 O 3 nanorods (NRs). Flower-like ZnO NRs with the average diameter about 810 nm and length about 4.5 µm were firstly synthesized via a chemical solution method, and then ZnO NRs was coated with a continuous α-Fe 2 O 3 layer to form ZnO/α-Fe 2 O 3 core-shell structure through an ionic-layer adsorption and reaction method. The gas-sensing results show that the ZnO/α-Fe 2 O 3 NRs exhibit excellent sensitivity, selectivity, and response-recovery capacity to ethanol vapor at a low optimum temperature of 240 °C. In particular, compared with pure ZnO NRs and α-Fe 2 O 3 nanoparticles (NPs), the ZnO/α-Fe 2 O 3 NRs show an obvious improvement in gas sensing properties. The substantial improvement of sensing properties may be attributed to the unique microstructure and heterojunction formed between ZnO and α-Fe 2 O 3 . [ABSTRACT FROM AUTHOR]

A novel lead-free, high dielectric constant, ultra-wide temperature stable dielectric ceramic Ba 1−x Bi x Ti 1−x −y Zn 0.75x W 0.25x+y O 3+y (0.22≤x≤0.30, y=0.015) was synthesized by the traditional solid-state reaction method. The phase composition, electric and dielectric properties of the Ba 1−x Bi x Ti 1−x −y Zn 0.75x W 0.25x+y O 3 ceramics were investigated. The P-V-L dielectric theory was introduced. And, the chemical bond energy was calculated to track the changes in micro-structure. The relationships between chemical bond energy and the macroscopic dielectric properties(ε r , dielectric stability and dielectric loss ) in Ba 1−x Bi x Ti 1−x−y Zn 0.75x W 0.25x+y O 3+y ceramics were discussed systematically. Owing to the inhomogeneous micro-structure and the diffusion in phase transition, Ba 1−x Bi x Ti 1−x−y Zn 0.75x W 0.25x+y O 3+y ceramics showed a stable permittivity (~800±15%) over a ultra-wide temperature range (−30 to 375 °C). Moreover, dielectric loss was less than 0.02 and the insulation resistance was over 10 12 Ω cm. These features suggested that the Ba 1−x Bi x Ti 1−x−y Zn 0.75x W 0.25x+y O 3+y ceramic could be considered as a promising candidate material for energy storage applications in harsh environment. [ABSTRACT FROM AUTHOR]

Multi-component BaTiO 3 –Bi 0.5 Na 0.5 TiO 3 –Nb 2 O 5 (BBNN) system doped with divalent metal ions (Zn 2+ , Co 2+ , Ni 2+ ) was prepared by the conventional solid–state method.The X-ray diffraction patterns revealed all samples exhibited perovskite (P4mm) single phase. The dielectric properties and micro-mechanisms were discussed and validated. Novel theories, based on the characteristics of the different kinds of dielectric polarization, are proposed to explain the dielectric anomalies in the dielectric system. The relationships between microstructure and the dielectric properties were investigated systematically for the first time. The samples doped with 15 mol% Zn 2+ /Co 2+ presented good dielectric properties of an ultra-broad temperature stable range (from −50 and >300), high dielectric constant (ε~1925 for Zn 2+ / ε~1341 for Co 2+ ) and low dielectric loss (tan δ<0.02) were obtained. These features made the ceramics system have high practical values for miniaturization and harsh environments applications. [ABSTRACT FROM AUTHOR]

Hafnium oxide (HfO 2) fibers can be widely used in ultra-high temperature ceramics (UHTCs) as reinforced material in order to achieve better antioxidant performance and less cracks and flaking on surface of UHTCs in field of ultra-high temperature thermal protectors. Calcination temperature is one of essential parameters for forming HfO 2 fiber. In this work, one-dimensional (HfO 2) fibers were prepared through the electrospinning method and further post-calcination treatment. During the calcination treatment, the monoclinic-HfO2 (m-HfO 2) was formed from as-spun HfO 2 fibers at 432 °C, and only a small amount of m-HfO 2 was converted into the tetragonal HfO 2 at 1013 °C, which can increase the fiber density and decrease the grain size. However, the remaining m-HfO 2 was directly converted into the cubic HfO 2 at 1351 °C. The unique temperatures of forming monoclinic, tetragonal, cubic phase were much lower than the phase-transition temperature. The prepared HfO 2 fiber could still maintain fibrous morphology after 10 times cyclic thermal shock in air. Moreover, the fibers calcined at 900 °C and 1200 °C have better thermal shock resistance for their stable phase and fibrous morphology with uniform grain growth after the thermal shock test. [ABSTRACT FROM AUTHOR]

BaSn 0.15 Ti 0.85 O 3 (BTS) thin films were deposited on Pt/Ti/SiO 2 /Si(1 0 0) substrate by pulsed laser deposition and the effects of substrate temperature on their structure, dielectric properties and leakage current density were investigated. The results indicate that the substrate temperature has a significant effect on the structural and dielectric properties of the BTS thin films which exhibit a polycrystalline perovskite structure if the substrate temperature ranges within 550–750 °C. The dielectric constant and loss tangent of the BTS thin films deposited at 650 °C are 341 and 0.009 at 1 MHz, respectively, the tunability is 72.1% at a dc bias field of 400 kV/cm, while the largest figure of merit (FOM) is 81.1. The effect of the substrate temperature on the leakage current of the BTS thin films is discussed. [ABSTRACT FROM AUTHOR]