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

Abstract

Remarkable structural changes take place during the metal to insulator first-order transition in Pr0.50 Ca0.50 CoO3: 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 (Nd2/3 La1/3) 0.5 Ca0.5 CoO3, 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. © 2010 The American Physical Society.