TRANSFORMATION TWINNING IN CARBON-DOPED PRCO2 MAGNETIC CRYSTALS

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 rhomb ohedral crystal is heavily twinned along the {110} and {211} planes. T he twinning mechanism was explored by analysing the reduction in cryst al symmetry due to the cubic-to-rhombohedral phase transformation. The origin of the twinning and the formation of four twin variants were a ttributed to the insertion of carbon interstitials into Co-4 tetrahedr a along the (3) over bar axis in the rhombohedral lattice, which corre sponds to one of the four equivalent [111] axes of the parent cubic la ttice.