(120) and (12(2)over-bar) monazite deformation twins

Unusual features of (1 2 0) and (1 2 2) deformation twins in monazite (monoclinic LaPO4) 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 (eta(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. Published by Elsevier Ltd on behalf of Acta Materialia Inc.