Search

Magnetic properties of fully oxygenated bare CuO nanoparticles have been investigated using magnetization, X-ray diffraction, neutron diffraction, and Raman scattering measurements. The Langevin field profile is clearly revealed in the isothermal magnetization of 8.8 nm CuO nanoparticle assembly even at 300 K, revealing a 172 times enhancement of the ferromagnetic responses over that of bulk CuO. Surface magnetization of 8.8 nm CuO reaches 18% of the core magnetization. The Cu spins in 8.8 nm CuO order below 400 K, which is 1.7 times higher than the 231 K observed in bulk CuO. A relatively simple magnetic structure that may be indexed using a modulation vector of (0.2, 0, 0.2) was found for the 8.8 nm CuO, but no magnetic incommensurability was observed in bulk CuO. The Cu spins in 8.8 nm CuO form spin density waves with length scales of 5 chemical unit cells long along the crystallographic a- and c-axis directions. Considerable amounts of electronic charge shift from around the Cu lattice sites toward the interconnecting regions of two neighboring Cu–Cu ions, resulting in a stronger ferromagnetic direct exchange interaction for the neighboring Cu spins in 8.8 nm CuO.

Neutron diffraction has been used for in-situ studying of the charge–discharge processes in commercial lithium batteries with LiFePO 4 (LFP) and graphite electrodes. The diffraction data were obtained with time-of-flight diffractometer in the process of three complete charge–discharge cycles performed at a low rate (0.1 C) at room temperature. The experimental data allowed detailed tracing of the multistage process of Li insertion into graphite followed by the formation of several LiC n phases, as well as the reversible transition of LiFePO 4 ↔ FePO 4 . A comparison of the charge–discharge processes in a battery with a pure LFP cathode and LFP containing ∼1% of vanadium (LFPV) is made. In the second case, an evidently larger part of the anode material passes into the final LiC 6 state. Analysis of the diffraction patterns of LFP and LFPV powders revealed a marked shrinkage of crystallite size in the LFPV case, which correlates with better electrochemical properties of LFPV compared to LFP.