Cu, Mg Codoped Bismuth Tantalate Pyrochlores: Crystal Structure, XPS Spectra, Thermal Expansion, and Electrical Properties

Abstract

The pyrochlore-type solid-solution formation in a Bi1.6Mg0.8–x Cu x Ta1.6O7.2−Δ system, synthesized for the first time, is observed at x ≤ 0.56. High-temperature X-ray diffraction showed that the pyrochlore phase exists in air up to 1080 °C, where its thermal decomposition leads to the segregation of (Mg,Cu)­Ta2O6. The thermal expansion coefficients of the end member, Bi1.6Mg0.24Cu0.56Ta1.6O7.2−Δ, increase from 3.3 × 10–6 °C–1 at room temperature up to 8.7 × 10–6 °C–1 at 930 °C. Rietveld refinement confirmed that the pyrochlore crystal structure is disordered with space group Fd3̅m:2 (Z = 8, no. 227). Doping with copper results in a modest expansion of the cubic unit cell, promotes sintering of the ceramic materials, and induces their red-brown color. X-ray photoelectron spectroscopy demonstrated that the states of Bi­(III) and Mg­(II) are not affected by doping, and the effective charge of tantalum cations is lower than +5, while the Cu­(II) states coexist with Cu­(I). The electron spin resonance spectra display a single line with g = 2.2, ascribed to the dipole-broadened Cu2+ signal. The dielectric permittivity of Bi1.6Mg0.8–x Cu x Ta1.6O7.2−Δ ceramics may achieve up to ∼105, with the dielectric loss tangent varying in the range from 0.2 up to 12. Multiple dielectric relaxations are found at room temperature and above for all samples.

Immobilizing Isatin-Schiff Base Complexes in NH2-UiO-66 for Highly Photocatalytic CO2 Reduction

“…The results are consistent with the Ni signals previously reported for immobilized Ni-based complexes. − All of the results indicate the presence of Ni­(II) in the modified catalyst based on NH 2 -UiO-66. Likewise, the XPS data of 66-IS-Co and 66-IS-Cu also prove the presence of Co­(II) and Cu­(II) in NH 2 -UiO-66 (Figures S3–S6), consistent with previously reported results. − The results of thermogravimetric analysis (TGA) under a nitrogen atmosphere (Figure S7) suggest that 66-IS-Ni , 66-IS-Co , and 66-IS-Cu exhibit excellent thermal stability of up to 400 °C . After PSM, all three catalysts retained high specific surface areas and CO 2 adsorption (Figures S8 and S9), with 66-IS-Cu showing the highest levels.…”

Significant Enhanced SO2 Resistance of Pt/SiO2 Catalysts by Building the Ultrathin Metal Oxide Shell for Benzene Catalytic Combustion

“…The Mg 1s XPS spectrum is shown in Figure 10a with a peak at around 1305.1 eV, which was identified as the Mg 2+ state. 49,50 It could be seen that after the reaction of the Pt/ SiO 2 @MgO catalyst in the SO 2 atmosphere, the relative content of Mg elements on its surface decreased, which was consistent with the data change in Table 5. In addition, the binding energies of the Zn 2p spectra were 1046.0 and 1022.9 eV, respectively (Figure 10b), indicating the presence of Zn 2+ species.…”

Electromagnetic Performance of NiMgCuZn Ferrite for Hyperthermia Application in Cancer Treatment

“…The Cu 2p 3/2 at 932.22 eV decomposed into two peaks: the first peak at 932.05 eV for Cu 2+ and the second peak at 932.63 eV for Cu + . Similarly, the peak at 952.02 eV was decomposed into 951.84 and 952.91 eV corresponding to the peaks of Cu 2+ and Cu + . The spectra of Fe 2p show peaks at 709.87 and 723.62 eV, which represent the 2p 3/2 state and 2p 1/2 state of Fe ions, respectively.…”