Effect of 3D Metal on Electrochemical Properties of Sodium Intercalation Cathode P2-NaxMe1/3Mn2/3O2 (M = Co, Ni, or Fe)

This research aims to evaluate the influence of different 3D metals (Fe, Co, and Ni) substituted to Mn on the electrochemical performance of P2-NaxMe1/3Mn2/3O2 material, which was synthesized by the coprecipitation process followed by calcination at high temperature. X-ray diffraction (XRD) results revealed that the synthesized Mn-rich materials possessed a P2-type structure with a negligible amount of oxide impurities. The materials possessed their typical cyclic voltammogram and charge-discharge profiles; indeed, a high reversible redox reaction was obtained by NaxCo1/3Mn2/3O2 sample. Both NaxCo1/3Mn2/3O2 and NaxFe1/3Mn2/3O2 provided a high specific capacity of above 140 mAh·g−1; however, the former showed better cycling performance with 83% capacity retention after 50 cycles at C/10 and high rate capability. Meanwhile, the Ni-sub NaxNi1/3Mn2/3O2 exhibited excellent cycling stability but a low specific capacity of 110 mAh·g−1 and inferior rate capability. The diffusion coefficient of Na+ ions into the structure tended to decrease with a depth of discharge; those values were in the range of 10−10–10−9 cm2·s−1 and 10−11–10−10 cm2·s−1 in the solid solution region and biphasic region, respectively.

Microstructure and polarization behavior of Ni/WC+GO (graphene oxide) composite cladding fusion coating

Ni/WC/graphene oxide (GO) composite cladding fusion coatings were fabricated through the vacuum cladding technique on a medium carbon structure steel (45# steel) substrate whose carbon content was 0.45 ± 0.03%. The microstructural characteristics, phase composition, and electrochemical polarization characteristics of the composite cladding fusion coatings were analyzed with scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, and the electrochemical workstation CHI660E. Results show that the microstructure was compact and was micro-crack free, and without inclusions or other defects. It was comprised of four micro-zones, namely, the composite, transition, diffusion fusion, and diffusion-affected zones with thicknesses of approximately 4 mm, 1 mm, 20 μm, and 250 μm, respectively. The main phases of the composite coating were γ-Ni solid solution, WC, Cr7C3, Ni2.9Cr0.7Fe0.36, Cr23C6, Ni3Fe, Ni3Si, Ni3B, W2C, and C. The self-corrosion potential of the composite coatings had increased by 0.3269 V compared with that of the substrate, and the corrosion current density of the composite coatings had decreased by nearly two orders of magnitude. The Ni-based solid solution region with relatively high C and Cr contents was difficult to dissolve.

Re-investigation of the structure and crystal chemistry of the Bi2O3–W2O6 `type (Ib)' solid solution using single-crystal neutron and synchrotron X-ray diffraction

Single crystals of composition Bi35.66W4.34O66.51 (or Bi8.2WO15.3, bismuth tungsten oxide), within the type (Ib) solid-solution region of the Bi2O3–WO3 system, were synthesized using the floating-zone furnace method. Synchrotron X-ray and neutron single-crystal diffraction data were used to confirm the previously tentative assignment of the room-temperature space group as I41. Fourier analysis of the combined X-ray and neutron datasets was used to elucidate and refine fully the cation and anion arrays for the first time. The mixed cation site M1 is shown to be coordinated by eight O atoms in an irregular cube when M = Bi, and by six O atoms in an octahedron when M = W. The resulting disorder in the average structure around M1 is discussed in the context of experimentally observed oxide-ion conductivity.

Microwave dielectric properties of (1 − x)Cu3Nb2O8−xZn3Nb2O8 ceramics

The sintering behavior and microwave dielectric properties of (1 − x)Cu3Nb2O8−xZn3Nb2O8 have been investigated using dilatometry, x-ray diffraction, and a network analyzer. It was found that (1 − x)Cu3Nb2O8−xZn3Nb2O8 ceramics have a much lower melting temperature than Zn3Nb2O8 ceramics without Cu3Nb2O8 additives. Samples sintered at 900 °C for 2 h exhibited densities >97% of the theoretical density. Cu3Nb2O8 acts as a sintering aid. Two phase regions were identified with increasing Zn3Nb2O8 contents. A Cu3Nb2O8−Zn3Nb2O8 solid solution exists from 0 < x < 0.5 while a mixture of Cu3Nb2O8 and Zn3Nb2O8 exists from 0.5 < x < 1. The microwave dielectric properties correlated to the crystal structure. In Cu3Nb2O8−Zn3Nb2O8 solid solution region, the variation of dielectric properties could be explained by the structure distortion of Cu3Nb2O8 due to electronic anisotropies of Cu2+ cations.

Phase Relations and Microwave Dielectric Properties of ZnNb2O6–TiO2

The phase relations and microwave dielectric properties of (1−x)ZnNb2O6–xTiO2 were investigated using x-ray powder diffraction and a network analyzer. Four phase regions were studied with increasing TiO2 mol% (x): columbite solid solution, ixiolite (ZnTiNb2O8) solid solution, mixture of ixiolite and rutile solid solutions, and rutile solid solution. It was suggested that the microwave properties depend on crystal structure rather than chemical composition. In the columbite solid solution region, an order–disorder transition was found with an increasing amount of TiO2, and the quality factor decreased sharply. ZnTiNb2O8 (x = 0.5), has a fully disordered structure and possesses a quality factor of 42,500, relative dielectric constant (εr) of 34.3, and temperature coefficient of resonant frequency (τf) of −52 ppm/°C. In the mixture region of ixiolite and rutile structure, τf was modified to around 0 ppm/°C.