Porous anodic aluminium oxide has a long history of practical application for corrosion protection and coloring. In the last few decades a lot of hi-tech applications of this material have been found owing to the discovery of anodization conditions leading to the formation of highly ordered porous structures with a narrow pore size distribution. Here we show that in-plane orientation of the porous system in anodic films on aluminium is fully determined by the intrinsic crystallographic orientation of the Al substrate. The anisotropy of aluminium oxidation rates on a scalloped metal-oxide interface leads to reorientation of Al spikes in certain directions, which builds up an in-plane orientational order on a macroscopic scale restricted by a crystallite size. This is a unique example of the inheritance of the substrate crystal structure by an amorphous film through a size difference of three orders of magnitude.

Anodic aluminum oxide has unique and highly attractive properties, including self-ordering of porous structure during anodization. Although anodization regimes leading to formation of highly ordered porous structures had been found experimentally, many aspects of the self-organization mechanism remain unsolved. Here, the detailed in situ small-angle X-ray diffraction study of the self-ordering in porous alumina films is reported. Structure evolution kinetics was deduced by a quantitative analysis of diffraction patterns combined with electron microscopy. The rate of pore ordering is shown to have maximal value at the initial anodization stage and rapidly decreases inversely proportional to t 0.2 . Self-organization is shown to occur via growth of domains possessing preferential in-plane orientation and "death" of other domains, similar to Ostwald ripening governed by difference in pore growth rates for domains of different orientations. The process is accompanied by pore death and splitting making a significant impact on anodic oxides utilization in any mass-transport issues. This finding opens a novel approach for growth of highly ordered porous anodic oxide films.

We demonstrate that the simultaneous substitution of calcium and aluminum for strontium and iron in strontium hexaferrite results in a significant increase of coercivity up to a record high of 21.3 kOe. We propose that the effect is originated from a crystal structure distortion causing an increase of the magnetocrystalline anisotropy.

No abstract

No abstract

No abstract

A quantitative analysis of long-range order in the self-organized porous structure of anodic alumina films has been performed on the basis of a microradian X-ray diffraction study. The structure is shown to possess orientational order over macroscopic distances larger than 1 mm. At the same time, the interpore positional order is only short-range and does not extend over more than $10 interpore distances. These positional correlations are mostly lost gradually rather than at the domain boundaries, as suggested by the divergence of the peak width for the higher-order reflections. In the direction of the film growth the pores have a very long longitudinal self-correlation length of the order of tens of micrometres.

No abstract