Influence of Low-Level Substitution Pr/(Sr or Ba) in PrMnO3 on Structure Distortions, Magnetic Transitions, and Surface Evolution

The comparative study on how the strontium or barium substitution level influences structural distortions, magnetic and surface characteristics of the perovskite-like PrMnO3 manganite was carried. In contrast to Pr0.75Ba0.25MnO3, the synthesized Pr1-xSrxMnO3 (x = 0; 0.15; 0.25) and Pr0.85Ba0.15MnO3 have an orbitally ordered structure with Jahn–Teller (JT) distortion at room temperature. The heterovalent substitution by Sr/Ba reduces the temperature of the order–disorder structural transition on heating. The substitution of praseodymium with a higher level of barium Pr0.75Ba0.25MnO3 initiates a structural transition to an orbitally disordered structure that is observed in the whole temperature range investigated (25–1150 ºC). The degree of energetic interaction between the substituted A—sublattice and O2− sublattice could influence the order–disorder structural transition. Magnetic measurements show the presence of a phase transition from the paramagnetic to the ferromagnetic state for all manganites. It was found that the Curie transition temperature increases as the Sr/Ba substitution level increases, which indicates the potential possibility of practical application of the studied manganites. The evolution of the structure and the magnetic behavior is explained by a decrease in the JT distortion with an increase in the substitution level. The X-ray photoelectron spectroscopy study demonstrates that for all considered manganites the oxidation state of manganese cations on the surface deviates from the expected charge balance, taking into account the bulk substitution. Stabilization of Pr3+ cations on the surface was noted.