TLS twinning

From Online Dictionary of Crystallography

TLS (Twin Lattice Symmetry) twinning is a term employed to indicate twinning where the twin lattice does not possess a pseudo-symmetry, differently from what happens in TLQS twinning.

In TLS twinning, the lattice row/lattice plane [uvw] / (hkl) defining the cell of the twin lattice are mutually perpendicular. When this perpendicularity is imposed by the symmetry of the lattice, one speaks of intrinsic-TLS (i-TLS). In all other cases, the conditions of perpendicularity depend on one or more metric parameters: one then speaks of extrinsic-TLS (e-TLS).