Strain-induced heteronuclear charge disproportionation in EuMnO₃

Charge disproportionation transitions commonly link high-temperature phases, in which cations of a given element have the same oxidation state, to low-temperature phases, where charge transfers between ions of this element results unequal oxidation states. Based on density functional theory calculations we here propose the concept of heteronuclear charge disproportionation, for which charge transfers occurs between different elements located on different crystallographic sites. Using EuMnO₃ as a test case, we show that the transition from Eu³⁺Mn³⁺O₃ to Eu²⁺Mn⁴⁺O₃ can be triggered by pressure or epitaxial strain. We will highlight experimentally accessible signatures of this transition and discuss other crystal chemistries that could show similar phase transitions and resulting novel physics.