Probing the structure of nanograined CuO powders

Abstract

The microstructural properties of polycrystalline CuO powders and their evolution during controlled high energetic ball milling (HEBM) were studied using conventional X-ray diffraction (XRD) techniques and in situ temperature-dependent small and wide angle scattering (SAXS-WAXS) synchrotron radiation experiments. Volume weighted average grain size, unit cell expansion, oxygen deficiency, and microstrain values as a function of milling time were obtained from XRD. SAXS data revealed different nanostructures for samples synthesized by one-step solid-state reaction (SSR) or HEBM-treated powders. The latter presented the characteristics of a multilayered nanoscale solid system with surface fractal behavior. Correlation of the XRD microstructural parameters and the power law exponent of the SAXS curves as a function of temperature and milling time provided a coherent picture of the structure of HEBM-treated powders. The overall structural information presented in this article may shed some light on the macroscopic physical properties of CuO nanostructures.

Influence of Pressure and Temperature on X-Ray Induced Photoreduction of Nanocrystalline CuO

“…Some evidence of the lattice expansion upon crystallite size reduction is observed; however, the effect is rather small. Note that the unit cell volume expansion was found previously in CuO powders with the average grain size of about 9.5-35.1 nm and explained by an influence of strain or oxygen depletion [23]. The effect of temperature on the X-ray induced photoreduction of nano-CuO (8 nm) is shown in Fig.…”

Magnetic hardness features and loop shift in nanostructured CuO

“…The possibility of coexistence of ferromagnetic phases with different coercivities (an even the contribution of a spin glass fraction) may be rationalized by the multilayer of coherently diffracting layers and rough interfaces model we have found suitable to explain small angle x ray scattering (SAXS) data coming from milled CuO samples. 42 These data have shown a correlation between the changes in D and the SAXS power law exponent (or surface fractal dimension) with milling time. 42,43 The proposed multilayer model is consistent with the nanoscale SEM image of S 2 , Fig.…”

“…42 These data have shown a correlation between the changes in D and the SAXS power law exponent (or surface fractal dimension) with milling time. 42,43 The proposed multilayer model is consistent with the nanoscale SEM image of S 2 , Fig. 2(d).…”

“…The interface layers, whose surfaces become rougher with milling time, enclose voids and defects which can originate regions with different oxygen content. 42,43 Thus, disordered interfaces probably originate an imbalance of the CuO antiferromagnetic lattice that gives rise to a net particle magnetic moment, which explains the observed FM behavior at RT. The strongly connected interface-layer regions in the multilayer-like configuration provides the FM/AFM coupling and the rougher interface surface 43 may be the cause for the observed relatively large loop shift effect along the field axis observed in S 2 sample.…”

Óxidos binarios antiferromagnéticos de metales de transición: relación estructura propiedad en nanoestructuras

“…Es de destacar que en este experimento sólo se detectaron líneas de difracción correspondientes al CuO a pesar de que la muestra se encontraba en vacío durante el tratamiento térmico. De no haber habido O 2 disponible los nanocristales habrían sufrido una transición de fase a Cu 2 O al superar los 500 K [35]. Esto nos permite suponer que el O habría migrado a la superficie fractal durante la MM, permaneció luego en la interfaz y fue liberado al modificarse la fractalidad de la superficie.…”