Valence state of Mn in charge-ordering Pr 0.5Ca 0.5MnO 3− δ studied by Mn 3s photoemission spectroscopy

Abstract

Mn 3s photoemission spectroscopy has been performed at 300 and 100 K for Pr 0.5Ca 0.5MnO 3− δ which undergoes a charge-ordering transition around 235 K with decreasing temperature. We have observed in the Mn 3s spectrum the change in the Mn valency of Pr 0.5Ca 0.5MnO 3− δ accompanied by the transition. The Mn 3s spectrum at 300 K for Pr 0.5Ca 0.5MnO 3− δ is nearly identical to that of La 1.2Sr 1.8Mn 2O 7 in which the formal valence of the Mn ion is +3.4. This is consistent with the fact that the oxygen deficiency δ is 0.05 for the present sample. On the other hand the Mn 3s spectrum at 100 K is well reproduced by a superposition of those for LiMnO 2 with Mn 3+ and for SrMnO 3 with Mn 4+, while the mean Mn valency at 100 K remains being +3.4. This indicates that the Mn ions in Pr 0.5Ca 0.5MnO 3− δ are in the two different valence states below the transition temperature.