Abstract A theoretical model is suggested which describes a non-conventional relaxation mechanism in strained high transition temperature superconducting films, namely the formation of nanograins with 90 • grain boundaries. It is theoretically revealed here that misfit stresses in superconducting thin films at early stages of their growth are effectively relaxed through the formation of nanograins with their crystal lattice misoriented by 90 • relative to the crystal lattice of the film matrix. With increasing film thickness, the formation of a continuous layer resulting from the convergence of nanograins becomes energetically favourable. The results of the model account for experimental data on the observation of nanograins with 90 • grain boundaries in YBaCuO films, reported in the literature
