Critical thickness of YBaCuO (123) strained thin films and superlattices grown by pulsed laser deposition

An energy model has been used to calculate the critical thickness hc of YBaCuO ultra-thin films and YBaCuO based superlattices. The calculated hc values of single layers are in good agreement with XRD measurements (5 ≤ hc ≤ 7.5 nm). In the case of YBa2Cu3O7PrBa2Cu3−xGaxO7 superlattices grown by PLD on {100} SrTiO3, the relaxation appears to be governed by the critical thickness of the elementary sub-layers, hc being lower than 4 YBaCuO cells (4.8 nm). The critical temperature of the superlattices seems to be only slightly affected by this expanded stress in contrast to that is observed when an elastic stress applied along the ab plane of YBaCuO thin films.