Multiple strain-induced phase transitions in LaNi O 3 thin films

Strain effects on epitaxial thin films of $\mathrm{LaNi}{\mathrm{O}}_{3}$ grown on different single crystalline substrates are studied by Raman scattering and first-principles simulation. New Raman modes, not present in bulk or fully relaxed films, appear under both compressive and tensile strains, indicating symmetry reductions. Interestingly, the Raman spectra and the underlying crystal symmetry for tensile and compressively strained films are different. Extensive mapping of $\mathrm{LaNi}{\mathrm{O}}_{3}$ phase stability is addressed by simulations, showing that a variety of crystalline phases are indeed stabilized under strain. The calculated Raman frequencies reproduce the principal features of the experimental spectra, supporting the validity of the multiple strain-driven structural transitions predicted by the simulations.