Role of A-site cations in the metal-insulator transition in Pr0.5Ca0.5CoO3−γ (γ≈0)

6 páginas, 4 figuras, 1 tabla.-- PACS number(s): 71.30.+h, 61.05.fm, 75.30.Kz, 75.47.De
Remarkable structural changes take place during the metal to insulator first-order transition in Pr0.50Ca0.50CoO3: a contraction of the unit-cell volume, the bending of the Co-O-Co bond angle, and a decrease in (Pr,Ca)-O bond distance. However, the Co-O bond length and the volume of the CoO6 octahedra remain almost unaltered during the transition. In view of these data and the absence of transition in (Nd2/3La1/3)0.5Ca0.5CoO3, we review the current spin-state transition picture, emphasizing that an active role is played by the A-site Pr cations that could be related with the effect of Pr in 123 superconducting cuprates.
Financial support from MICINN (Spanish government) under Projects No. MAT2006-11080-C02-02 and No. NANOSELECT CSD2007-00041, Generalitat de Catalunya (Grant No. 2005-GRQ-00509) and FAME European Network of Excellence is acknowledged.