(1 2 0) and (1 2 2̄) monazite deformation twins

Abstract Unusual features of (1 2 0) and (1 2 2) deformation twins in monazite (monoclinic LaPO 4 ) are described and analyzed. These features are kinks and other irregularities in (1 2 0) twins, and V-shaped indentations on (1 2 0) and (1 2 2) twin planes. Twinning shear analysis suggests that the kinks are a type II deformation twin mode with shear direction ( η 1 ) of [2 1 0]. This complements previous analysis based on atom shuffling considerations. Shear strain compatibility requires extensive plastic deformation in the kink. The V-shaped indentations may be analogous to similar structures in b.c.c metal deformation twins. Deformation mechanisms that may be associated with these structures are discussed.