Accurate determination of domain boundary orientation in LaNbO4

The orientation relationship between ferroelastic domains in LaNbO4 (with 0.5 at.% Sr) is studied by selected area electron diffraction and high-resolution electron microscopy. At room temperature the domains are related through a simple rotation of approximately 95° about the monoclinic [0 1 0] axis, and the interface between two adjacent domains is highly ordered. The domain boundary is found to be the (2 0 −5.10)/(5.10 0 2) planes of the two domains, in excellent agreement with our theoretical predictions. This orientation differs considerably from that predicted by more elaborate ferroelastic theory.