Cationic ordering in Sr2FeReO6 (SFRO) and Sr2CrReO6 (SCRO) is investigated using magnetic property measurement, atomic-scale imaging, and first-principles calculations. We find that the nature of cationic ordering strongly depends on the host oxides, although they have the same crystal symmetry and chemical formula. Firstly, adding Re is effective to enhance the cationic ordering in SFRO, but makes it worse in SCRO. Secondly, the microscopic structure of antisite (AS) defects, associated with the level of cationic ordering, is also distinguishable; the AS defects in SFRO are clustered in the form of an antiphase-boundary-like feature, while they are randomly scattered in SCRO. Interestingly, we observe that the clustered AS defects deteriorate the ferromagnetism more than the scattered defects. Our findings elevate the importance of the AS defect configuration as well as the amount of defects in terms of magnetic property.

Metamorphic (crystalline-to-amorphous) transition and consequent microstructural change were investigated in relation with the wear-resistance during the wear process of Fe-base metamorphic coating layer. The spray coating was accomplished using a detonation gun with various fuel gas conditions. The spray coated layer exhibited significantly improved wear resistance, which is about 45 times higher than that of the noncoated substrate. The significantly low friction coefficient and high hardness, resulting from the presence of amorphous surface film, seems to be the main cause of the improved wear-resistance. Electron microscopy on the cross-section of the coated layer exhibited intra-particle micro-segregations associated with rod-shape Cr and B rich particles and Fe-Cr solid solution phase. From the observations using TEM and EDS, Fe-Cr solid solution with supersaturated B and Si content seems to be the main phase contributing to the crystalline-to-amorphous transition during wear.

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