  It is often observed that martensitic microstructures in adjacent polycrystal
grains are related. For example, micrographs of Arlt exhibit propagation of
layered structures across grain boundaries in the cubic-to-tetragonal phase
transformation in $\rm BaTiO_3$. Such observations are related to requirements
of compatibility of the deformation at the grain boundary. Using a
generalization of the Hadamard jump condition, this is explored in the
nonlinear elasticity model of martensitic transformations for the case of a
bicrystal with suitably oriented columnar geometry, in which the microstructure
in both grains is assumed to involve just two martensitic variants, with a
planar or non-planar interface between the grains.
