Local polarization in oxygen-deficient LaMnO₃ induced by charge localization in the Jahn-Teller distorted structure

The functional properties of transition metal oxides result from a complex interplay between magnetism, polarization, strain, and stoichiometry. Here, we show that for materials with a cooperative Jahn-Teller distortion, such as LaMnO₃ (LMO), the orbital order can also couple to the defect chemistry and induce novel material properties. At low temperatures, LMO is an A-type antiferromagnet with a distorted orthorhombic perovskite structure. It is insulating due to the Jahn-Teller distortion that splits the e_g orbitals of the high-spin Mn³⁺ ions, leading to alternating long, short, and intermediate Mn-O bond lengths. Our DFT+U calculations show that, as a result of these peculiarities, the charge localization in LMO upon oxygen vacancy (V_O) formation is different compared to other manganites, like SrMnO₃, where the two extra electrons reduce the Mn sites adjacent to the vacancy. In LMO, relaxations around the V_O depend on which type of Mn-O bond is broken, affecting the d-orbital energies and leading to an asymmetric and hence polar localization of the excess electrons with respect to the vacancy. Furthermore, we show how isostatic and epitaxial strain can be used to affect the Mn-O bond lengths and orbital order and consequently the charge localization and polarity.