Simultaneous valence shift of Pr and Tb ions at the spin-state transition in ((Pr${}_{1-y}$Tb${}_y{)}_{0.7}$Ca${}_{0.3}$CoO${}_3$

Abstract

Temperature dependence of the X-ray absorption near-edge structure (XANES) spectra at the Pr $L_3$- and Tb $L_3$-edges was measured for the (Pr${}_{1-y}$Tb${}_y{)}_{0.7}$Ca${}_{0.3}$CoO${}_3$ system, in which a metal-insulator (MI) and spin-state (SS) transition took place simultaneously at a critical temperature $T_{\mathrm{MI}}$. A small increase in the valence of the terbium ion was found below $T_{\mathrm{MI}}$, besides the enhancement of the praseodymium valence; the trivalent states, which are stable at room temperature, change to a 3+/4+ ionic mixture at low temperatures. In particular for the $y$=0.2 sample, the average valence determined at 8 K amounts to 3.03+ and 3.25+ for the Tb and Pr ion, respectively. In analogous (Pr${}_{1-y}$RE${}_y{)}_{0.7}$Ca${}_{0.3}$CoO${}_3$ samples (RE=Sm and Eu), in which the MI-SS transition also took place, no valence shift of the RE ion was detected in the XANES spectra at the RE ion $L_3$-edge. The role of the substituted RE ion for the Pr-site on the MI-SS transition is discussed.

References in corpus (2)

• Valence change of praseodymium in Pr0.5Ca0.5CoO3 investigated by x-ray absorption spectroscopy
• Coupled valence and spin state transition in (Pr0.7Sm0.3)0.7Ca0.3CoO3

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