Origin of the non-linear pressure effects in perovskite manganites: Buckling of Mn–O–Mn bonds and Jahn–Teller distortion of the MnO6 octahedra induced by pressure

High-pressure resistivity and X-ray diffraction measurements were conducted on La0.85MnO3−δ at ∼6 and ∼7 GPa, respectively. At low pressures the metal–insulator transition temperature (TMI) increases linearly up to a critical pressure, P* ∼3.4 GPa, followed by reduction in TMI at higher pressure. Analysis of the bond distances and bond angles reveals that a bandwidth increase drives the increase in TMI below P*. The reduction in TMI at higher pressures is found to result from Jahn–Teller distortions of the MnO6 octahedra. The role of anharmonic interatomic potentials is discussed.