Phase diagram of BiFeO3/LaFeO3 superlattices: antiferroelectric-like state stability arising from strain effects and symmetry mismatch at heterointerfaces

(BiFeO3)(1−x)Λ/(LaFeO3)xΛ superlattices (SLs) have been grown using pulsed laser deposition and studied by X‐ray diffraction, transmission electron microscopy (TEM), and Raman spectroscopy. The composition is varied, 0.30 ≤ x ≤ 0.85, while the modulation period Λ is kept constant at about 10 nm. Unit cell doubling signatures typical of orthorhombic Pnma symmetry for x = 0.80 and 0.85 SLs and ¼{011} antiferroelectric PbZrO3‐like reflections in SLs with 0.30 ≤ x ≤ 0.7 are detected by TEM showing a complex structural mixture at the nanoscale level. The Raman spectra confirm these observations and show a change in the SLs from a Pnma LaFeO3‐like spectra for LaFeO3‐rich period to a PbZrO3‐like spectra for BiFeO3‐rich period. Electron–phonon interactions and resonant‐like excitations are also observed in the SLs. A temperature‐dependent X‐ray diffraction investigation shows a large shift of the paraelectric‐antiferroelectric phase transition scaling with the BiFeO3 thickness. This shift is correlated with the strain state and can be explained by a strong interplay between octahedral rotation/tilt and antipolar Bi displacement. Thickness–temperature phase diagram is constructed and differs from previous report showing the extreme sensitivity of the BiFeO3 phase stability to strain effects and rotation/tilt degrees of freedom.