Influence of strain relaxation on the structural stabilization of SmNiO3 films epitaxially grown on (0 0 1) SrTiO3 substrates

The structural stabilization of SmNiO3 (SNO) films epitaxially grown by an injection MO-CVD process on (0 0 1) SrTiO3 (STO) substrates is investigated. Using high-resolution X-ray diffraction (XRD), we show that SNO can be stabilized on STO with a minor amount of secondary phases and with a layer thickness reaching several hundreds of nanometers. The film quality is discussed by means of the simulation of X-ray reflectivity and XRD profiles that evidence smooth surfaces and interfaces. The actual lattice parameter of bulk (i.e. strain free) SNO is calculated as a function of the deposited thickness. It turns out firstly that the stabilization of SNO is achieved because the lattice mismatch between STO and SNO is not as high as expected (1.6% instead of 2.8%) and secondly the layer chemical composition varies with the film thickness. Finally, the well-known dissociation of the SNO phase into NiO and Sm2O3 is clearly correlated to the relaxation of epitaxial strain.