Magnetic properties of synthetic Ni

The present study focuses on the magnetic properties of the nanotubular Ni3Si2O5(OH)4 pecoraite, the structural analogue of chrysotile, obtained by hydrothermal synthesis. The cell parameters of the material, determined by X-ray diffraction, are $a=0.528(1)\ \text{nm}$ , $b=0.917(0)\ \text{nm}$ , $c=1.460(1)\ \text{nm}$ and $\beta=92.4(7)^{\circ}$ . The element analysis revealed the decrease of the Ni:Si ratio after hydrothermal treatment. The synthesized nanotubes have bigger outer and inner diameters in comparison to chrysotile. Using a vibration sample magnetometer, we determined the temperature of the ferromagnetic transition (23.7 K), $\mu_{\mathrm{eff}}$ of the $\text{Ni}^{2+}$ ion in pecoraite $(3.48\ \mu \text{B})$ and the blocking temperature (18 K)

Structural and electrical properties of Mg–Cu- and Mg–Cu–Li-doped bismuth niobate semiconductors with the pyrochlore structure

This work studies a series of synthesized Bi$_{1.6}$Mg$_{0.8-x}$Cu$_x$Nb$_{1.6}$O$_{7-\delta}$ ($x$ = 0.2, 0.4) semiconductors and their Lidoped compositions. A detailed structure investigation combining high-resolution neutron-, synchrotron-, and X-ray diffraction methods, as well as DFT calculations, revealed the preferential location of Cu and Li atoms at the Bi sites and Mg atoms at the Nb ones. According to high-temperature X-ray diffraction data, a structural modification caused by the activation of oxygen transport occurs at 200°C. The linear thermal expansion coefficient was found to be 3.6–4.6⋅10$^{−6}$ K$^{−1}$ (50–400°C). Magnetic susceptibility measurements allowed us to determine weak antiferromagnetic exchange interactions. The direct band gap was predicted using the DFTHSE03 hybrid functional calculation, and the optical direct band gap was estimated at 2.3–2.4 eV. Impedance spectroscopy and a dc four-probe technique were also employed to examine the samples$^,$ electrical properties. The high mixed electronic-ionic conductivity of the pyrochlores was detected, while the vacancies created by Lidoping in Bi$_{1.5-y}$Li$_y$Mg$_{0,375}$Cu$_{0,375}$Nb$_{1.5}$O$_{7-\delta}$ have been found not to affect the conductivity. Besides, the pyrochlores are chemically compatible with the La$_{0.7}$Sr$_{0.3}$MnO$_3$ perovskite (up to 800°C). These make us believe that the studied Mg–Cu- and Mg–Cu–Li-doped bismuth niobate semiconductors can become the basis for composite electrodes to boost their oxygen conductivity