Transformation twinning in carbon-doped PrCo2 magnetic crystals

摘要

A rhombohedral PrCo2Cx (x = 0.05-0.25) phase (space group, R (3) over bar m) was observed and characterized in an original cubic PrCo2 hard magnet (space group, Fd (3) over bar m) after adding carbon. The rhombohedral crystal is heavily twinned along the {110} and {211} planes. The twinning mechanism was explored by analysing the reduction in crystal symmetry due to the cubic-to-rhombohedral phase transformation. The origin of the twinning and the formation of four twin variants were attributed to the insertion of carbon interstitials into Co-4 tetrahedra along the (3) over bar axis in the rhombohedral lattice, which corresponds to one of the four equivalent [111] axes of the parent cubic lattice.