Physical Review B 110, 064305 (2024)

Lead-free antiferroelectric perovskite AgNbO3 is nowadaysattracting extensive research interests due to its promising applications inenergy storage. Although great progress has been made in optimizing thematerial performance, fundamental questions remain regarding the mechanismstabilizing the antiferroelectric Pbcm phase. Here, combining structuralsymmetry analysis and first-principles calculations, we identified crucial anharmoniccouplings of oxygen octahedra rotations and cation antipolar motions thatcontribute significantly to lowering the energy of the Pbcm phase. Thestabilization of this phase shows close similarities with the stabilization ofthe Pbam phase in PbZrO3 except that in AgNbO3 the octahedra rotations are theprimary distortions while the antipolar cation motions appear to be secondary.The appearance and significant amplitude of the latter are explained from thecombination of hybrid-improper and triggered mechanisms.

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