  A wide family of cobalt oxides of formulation (Pr,Ln,Ca)CoO3 (Ln being a
lanthanide) exhibits a coupled valence and spin-state transition (VSST) at a
temperature T*, which involves two concomitant modifications: (i) a change in
the spin state of Co3+ from low-spin (T < T*) to a higher spin-state (T > T*),
and (ii) a change in the valence state of Pr, from a mixed Pr4+/Pr3+ state (T <
T*) to a purely trivalent state (T > T*), accompanied by an equivalent charge
transfer within the Co3+/Co4+ subsystem. In the present paper, the VSST taking
place in (Pr0.7Sm0.3)0.7Ca0.3CoO3 at T* = about 90 K is investigated by
magnetization and heat capacity measurements. First, we quantitatively
characterized the jumps in magnetic susceptibility (khi) and entropy (S) around
T*. Then, these values were compared to those calculated as a function of the
variations in the population of the different cationic species involved in the
VSST. X-ray absorption spectroscopy experiments recently showed that the higher
spin state above T* should be regarded as an inhomogeneous mixture between
low-spin (LS) and high-spin (HS) states. In the frame of this description, we
demonstrate that the jumps in both khi and S can be associated to the same
change in the Co3+ HS content around T*. This result lends further support to
the relevance of the LS/HS picture for the VSST, challenging the currently
dominant interpretation based on the occurrence of an intermediate-spin (IS)
state of Co3+ above T*.
