Mechanical and correlated electronic transport properties of preferentially orientated SmNiO3 films

Although the correlated rare-earth nickelate perovskites (such as SmNiO3) exhibit remarkable metal to insulator transitions (MIT) beyond conventional semiconductors, their respective variations in mechanical properties during MIT remain yet unknown. Exploring the intrinsic mechanical properties of SmNiO3 is largely prohibited since it is theoretically impossible to grow the single crystalline samples in a large size as required for conventional characterizations. For the first time, we performed nano-indentation tests of preferentially oriented SmNiO3 films with thickness approaching micrometer scale epitaxy on single crystalline LaAlO3 substrates, and the corresponding temperature-dependent mechanical properties are characterized. As-grown SmNiO3 thick films experience sharp transitions in electrical resistivity across MIT, while their insulating phases exhibit thermistor transportation behaviors with the negative temperature dependence of resistance within a broad range of temperature. Nano-indentation tests at room and elevated temperature regions (25-200 degrees C) are performed for harvesting the Vickers hardness and elastic modulus at different temperatures. In addition, it is also interesting to note that these mechanical properties remain relatively stable during MIT, despite the structural twisting in their NiO6 octahedron during the MIT as previously known for SmNiO3. The SmNiO3 is shown to be relatively soft among the family of perovskite oxides, while its mechanical properties are insensitive to increase temperature across its metal to insulator transitions. It paves the way for further applying rare-earth nickelates in the field of correlation electronics.