Mechanical properties of the hexagonal HoMnO₃ thin films by nanoindentation

The structural and nanomechanical characteristics of the hexagonal HoMnO₃ (HMO) thin films are investigated by means of X-ray diffraction (XRD), atomic force microscopy (AFM) and nanoindentation techniques in this study. The HMO thin films were deposited on YSZ(1 1 1) substrates by pulsed laser deposition (PLD). The XRD results reveal only pure (0 0 0 1)-oriented hexagonal HMO reflections without any discernible traces of impurity or secondary phases. Nanoindentation results exhibit discontinuities in the load-displacement curve (so-called multiple "pop-ins" event) during loading, indicating possible involvement of dislocation activities. No discontinuities were observed on unloading segment of the load-displacement curve. Continuous stiffness measurements (CSM) technique was carried out in the nanoindentation tests to determine the hardness and Young's modulus of the hexagonal HMO thin films. The obtained hardness and Young's modulus of the hexagonal HMO thin films are 14.2 ± 0.7 GPa and 219.2 ± 10.6 GPa, respectively with the room-temperature fracture toughness being in the order of 0.4 ± 0.2 MPa m^1/2.