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The changes of physical properties occurring at a first-order-like transition among a wide family of (Pr1-yLny)1-xCaxCoO3 compounds (Ln being a lanthanide) are controversially discussed as a transition of Co3+ ions from states of low spin (LS) to intermediate spin (IS), or from LS to a mixture of LS and high spin (HS). The debate also includes the nature of the spin state of Co4+, as well as the degree of valence shift between Pr3+ and Pr4+ which accompanies this transition. In the present paper, we investigated the evolution of spin and valence states of Co ions and the valence state of Pr ions in (Pr0.7Sm0.3)0.7Ca0.3CoO 3 , at high temperature up to 750 K and under pressure up to 36.5 GPa. For this purpose, the data of three spectroscopic techniques were combined: high-resolution Co K-edge partial-fluorescence-yield x-ray absorption spectra, Pr L2-edge x-ray absorption spectra, and Co K β x-ray emission spectra. The spectral weight transfer of the pre-edge peaks of the Co K-edge spectra reveals a continuous redistribution of 3d electrons between the t2g and eg levels of Co ions, reflecting a gradual increase of the average Co spin state upon heating. This is further confirmed by Co K β x-ray emission spectra, which show an increase of HS Co3+ population when increasing temperature from 300 to 750 K. Applying high pressure at 300 K, the Co K β x-ray emission spectra indicate a relatively sharp increase of LS Co3+ population below 4 GPa. Pr L2-edge x-ray absorption spectra of (Pr0.7Sm0.3)0.7Ca0.3CoO3 exhibit a valence-state transition from Pr3+ to Pr3.26+, occurring predominantly upon applying pressure in the range ~ 4 to ~ 12 GPa. Owing to the charge balance, increasing pressure in this regime induces complex valence and spin-state transitions within the Co ions. Moreover, at high enough pressure, it is found that the Co4+ can also undergo a spin-state transition (from IS to LS), in addition to that affecting the Co3+ (HS to LS). [ABSTRACT FROM AUTHOR]

Ba2Co9O14 is a charge-ordered Co2+/3+ cobaltite that consists of building blocks of Cdl2-type Co2+/3+O6/3 layers, face-shared Co3+3O12 octahedral trimers, and corner-sharing Co2+04 tetrahedra. The Co-L2,3 x-ray absorption spectroscopy spectrum at room temperature indicates a high and a low spin state for Co2+ and Co3+ ions, respectively. Measurements of high-temperature resistivity and thermoelectric power revealed an insulator-to-insulator phase transition at Tt = 570 K, above which the inverse magnetic susceptibility X-1(T) deviates from the Curie-Weiss law. By using a combination of soft x-ray absorption spectroscopy at the O-K edge and high-resolution synchrotron x-ray powder diffraction measurements on crossing Tt, we have successfully determined the origin of this phase transition as a low-to-higher spin-state transition of Co3+ ions within the face-shared Co3O12 octahedral trimers in Ba2Co9O14. [ABSTRACT FROM AUTHOR]