Structural Phase Transitions and Magnetic Superexchange in M(I)Ag(II)F(3) Perovskites at High Pressure

Pressure‐induced phase transitions of M(I)Ag(II)F(3) perovskites (M=K, Rb, Cs) have been predicted theoretically for the first time for pressures up to 100 GPa. The sequence of phase transitions for M=K and Rb consists of a transition from orthorhombic to monoclinic and back to orthorhombic, associated with progressive bending of infinite chains of corner‐sharing [AgF(6)](4−) octahedra and their mutual approach through secondary Ag⋅⋅⋅F contacts. In stark contrast, only a single phase transition (tetragonal→triclinic) is predicted for CsAgF(3); this is associated with substantial deformation of the Jahn–Teller‐distorted first coordination sphere of Ag(II) and association of the infinite [AgF(6)](4−) chains into a polymeric sublattice. The phase transitions markedly decrease the coupling strength of intra‐chain antiferromagnetic superexchange in MAgF(3) hosts lattices.