Valence changes of manganese and structural phase transitions in Sr1−xPrxMnO3 (0.1≤x≤0.6)

Fifteen perovskite manganites Sr1−xPrxMnO3, x=0.1−0.6 in steps as fine as 0.025, have been synthesized by solid state methods and their crystal structures determined using synchrotron X-ray powder diffraction. At room temperature two first order phase transitions associated with changes in the orbital ordering and the tilting of the corner shared MnO6 octahedra are evident cubic/Pm3¯m⟹x≈0.15tetragonal/(I4/mcm)⟹x≈0.45orthorhombic/Imma, with two phase regions associated with both transitions. Heating the Pr rich oxide Sr0.5Pr0.5MnO3 provides a rare example where chemical pressure and temperature result in a different sequence of transitions Imma  –R3¯c–Pm3¯m, reflecting the importance of the Pr 4f electrons. X-ray absorption near-edge structure (XANES) measurements at the Mn K and Pr L3 edges show the valence state of the Mn linearly decreases with increasing Pr content whereas the Pr remains +3 across the entire series. Magnetic susceptibility measurements for selected samples are presented.

The Mn oxidation state and the phase diagram of Sr1−xPrxMnO3 (0.1► Structures of Sr1−xPrxMnO3, x=0.1–0.6, established using synchrotron XRD.
► Two first order phase transitions due to orbital ordering and the tilting of MnO6 octahedra observed.
► High temperature phase transitions investigated.
► Valence state of Mn and Pr determined using XANES.