Ground state and the metal-insulator transition in (Pr1-y Y y )1-x Ca x CoO3 (0.45 aparts per thousandcurrency sign x aparts per thousandcurrency sign 0.55) cobaltites

Pr0.5Ca0.5CoO3 exhibits a non-conventional metal-insulator transition (MIT) in which the insulating state is due toa volume contraction (similar to 2%) and electron transfer from Pr to Co sites. Pr1-x Ca (x) CoO(3)cobaltites with Ca doping around x similar to 0.5 (0.45 a parts per thousand currency sign x a parts per thousand currency sign 0.55) have been investigated. Different ground states and phase transitions are reported in samples at both sides of the half-doped composition. The relevance of the Pr/Ca ratio around half-doping and the amplitude of the changes observed at the MIT are analyzed. Besides the expected variation in the transition temperature, we report an enhanced Pr3+/Pr4+ transformation at the MIT in Pr0.45Y0.05Ca0.50CoO3[0.25(5) e(-)/Pr ion and T (MI) = 120 K] with respect to Pr0.5Ca0.5CoO3[0.15(5) e(-)/ Pr ion and T (MI) = 75 K].