Determination of the structure of the orthorhombic commensurate superlattice state of 2H-TaSe₂ by convergent-beam electron diffraction

Based on the analysis of higher-order Laue zone diffraction by Bird (1985), the structure of the commensurate superlattice state of 2H-TaSe₂ is determined by convergent-beam electron diffraction. It is shown that the most general displacements allowed by the orthorhombic space group can be described by a set of displacement waves. Only those waves with wavevector ¹/₃a* and Sigma ₁ symmetry have significant amplitudes. The final displacement pattern shows that each layer is strongly orthorhombic, in contrast with some recent Landau theory predictions.