Precise measurement of lattice parameters of pseudocubic lattices

For accurate measurements of lattice parameters of materials where symmetry differs only slightly from cubic, difficulties arise in the determination of single lines belonging to the lattice of Dower symmetry because of the overlapping profiles of the pseudocubic lines. In this contribution the profiles of single lines of lower symmetry are approximated by the Cauchy curve and the profiles of the pseudocubic lines are considered as superpositioning of these curves. The resolution of the profiles and the determination of the lattice parameters are performed by means of a computer fitting least-squares program. The conditions for solving the problem are discussed and the method is then applied to a pseudocubic perovskite.