Phase transition in Pr0.5Ca0.5CoO3 and related cobaltites

Abstract

We present an extensive investigation (magnetic, electric and thermal measurements and X-ray absorption spectroscopy) of the Pr0.5Ca0.5CoO3 and (Pr1-yYy)0.7Ca0.3CoO3 (y=0.0625-0.15) perovskites, in which a peculiar metal-insulator (M-I) transition, accompanied with pronounced structural and magnetic anomalies, occurs at 76 K and 40-132 K, respectively. The inspection of the M-I transition using the XANES data of Pr L3-edge and Co K-edge proofs the presence of Pr4+ ions at low temperatures and indicates simultaneously the intermediate spin to low spin crossover of Co species on lowering the temperature. The study thus definitively confirms the synchronicity of the electron transfer between Pr3+ ions and Co^(3+/4+)O3 subsystem and the transition to the low-spin, less electrically conducting phase. The large extent of the transfer is evidenced by the good quantitative agreement of the determined amount of the Pr4+ species, obtained either from the temperature dependence of the XANES spectra or via integration of the magnetic entropy change over the Pr4+ related Schottky peak in the low-temperature specific heat. These results show that the average valence of Pr3+/Pr4+ ions increases (in concomitance with the decrease of the formal Co valence) below TMI for (Pr0.925Y0.075)0.7Ca0.3CoO3 up to 3.16+ (the doping level of the CoO3 subsystem decreases from 3.30+ to 3.20+), for (Pr0.85Y0.15)0.7Ca0.3CoO3 up to 3.28+ (the decrease of doping level from 3.30+ to 3.13+) and for Pr0.5Ca0.5CoO3 up to 3.46+ (the decrease of doping level from 3.50+ to 3.27+).

19 pages, 11 figures

References in corpus (2)

• Disorder-Driven Non-Fermi Liquid Behavior of Correlated Electrons
• Valence change of praseodymium in Pr0.5Ca0.5CoO3 investigated by x-ray absorption spectroscopy

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• Competing phases in a model of Pr-based cobaltites
• Valence skipping, internal doping and site-selective Mott transition in PbCoO${}_3$ under pressure
• Quantum paramagnet near spin-state transition
• Revisiting spin ice physics in the ferromagnetic Ising pyrochlore Pr${}_2$Sn${}_2$O${}_7$
• Effects of magnetic fields and orbital angular momentum on excitonic condensation in two-orbital Hubbard model