Strain-dependent structure and Raman behaviours in the heavy-ion irradiated manganite at extreme low dose

The microstrains in heavy-ion irradiated manganite LaMnO₃ can be managed in linear response of irradiation dose, and the corresponding internal pressure up to 8 GPa can be induced by varying doses. The response of structure under stress is studied by means of Density Functional Theory and Lattice Dynamic Calculation. All obtained Raman scattering lines are discussed in details to shed light onto structural changes during ion implantation. There appears new resonance peak at around 550 cm^-1, which splits from broad features in the spectra, and attributes to the anti-symmetric vibrations of O₆ cages. The blue shift of this peak scales to ~2.4 cm^-1 per 1 GPa of stress. Another strong feature showing considerable blue shift is seen in the vicinity of 640 cm^-1 and corresponds to one of rhombohedral distortion related soft modes. A weak mode, not frequently reported, is seen at around 420 cm^-1 and corresponds to translation-like motions of fixed O₆ cages.