Nanoindentation of LaCrO3 thin films

Nanoindentation of LaCrO3 thin films deposited by radio-frequency magnetron sputtering onto stainless steel substrates was performed using an XP Nanoindenter. The “as-deposited” film was amorphous but transformed to an orthorhombic LaCrO3 perovskite structure after annealing at 1073 K for 1 h. The film thickness in the “as-deposited” state was 800 nm. Single loading/unloadings were performed in the displacement control mode on the crystalline film using different maximum displacements (50, 200, 400, and 800 nm). Therefore, the integral response of the film−substrate system was probed at different distances from the substrate. Nanoindentation experiments on LaCrO3 perovskite films revealed sharp “pop-in” events at certain loads. Such “pop-ins”, are most likely caused by the orthorhombic-to-rhombohedral phase transition which is known to occur in a LaCrO3 perovskite structure under pressure. However, such discontinuities have never been observed upon indentation of the amorphous “as-deposited” La-Cr-O thin films, and the pressure found to be typical of this transition in the LaCrO3 thin films is higher than previous bulk LaCrO3 sample studies. Mechanical characteristics of the films, such as hardness and Young’s modulus, were also measured.