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

Ricca, Chiara; Niederhauser, Nicolas; Aschauer, Ulrich (2020). Local polarization in oxygen-deficient LaMnO₃ induced by charge localization in the Jahn-Teller distorted structure. Physical review research, 2(4) American Physical Society 10.1103/PhysRevResearch.2.042040

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The functional properties of transition metal perovskite oxides are known to result from a complex interplay of 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 exhibits a strong Jahn-Teller distortion that splits the eg orbitals of the high-spin Mn3+ ions and leads to alternating long, short, and intermediate Mn-O bonds. Our DFT+U calculations show that, as a result of this orbital order, the charge localization in LMO upon oxygen vacancy formation differs from other manganites, such as SrMnO3, where the two extra electrons reduce the two Mn sites adjacent to the vacancy. In LMO, relaxations around the defect depend on which type of Mn-O bond is broken, affecting the d-orbital energies and leading to asymmetric and hence polar excess-electron localization with respect to the vacancy. Moreover, we show that the Mn-O bond lengths, the orbital order, and consequently the charge localization and polarity are tunable via strain.

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