Coupled valence and spin state transition in (Pr0.7Sm0.3)0.7

Abstract

The coupled valence and spin state transition (VSST) taking place in (Pr0.7Sm0.3)0.7Ca0.3CoO3 was investigated by soft x-ray absorption spectroscopy (XAS) experiments carried out at the Pr-M4,5, Co-L2,3, and O-1s edges. This VSST is found to be composed of a sharp Pr/Co valence and Co spin state transition centered at T*=89.3 K, followed by a smoother Co spin-state evolution at higher temperatures. At T < T*, we found that the praseodymium displays a mixed valence Pr3+/Pr4+ with about 0.13 Pr4+/f.u., while all the Co3+ is in the low-spin (LS) state. At T around T*, the sharp valence transition converts all the Pr4+ to Pr3+ with a corresponding Co3+ to Co4+ compensation. This is accompanied by an equally sharp spin state transition of the Co3+ from the low to an incoherent mixture of low and high spin (HS) states. An involvement of the intermediate spin (IS) state can be discarded for the Co3+. While above T* and at high temperatures the system shares rather similar properties as Sr-doped LaCoO3, at low temperatures it behaves much more like EuCoO3 with its highly stable LS configuration for the Co3+. Apparently, the mechanism responsible for the formation of Pr4+ at low temperatures also helps to stabilize the Co3+ in the LS configuration despite the presence of Co4+ ions. We also found out that that the Co4+ is in an IS state over the entire temperature range investigated in this study (10-290 K). The presence of Co3+ HS and Co4+ IS at elevated temperatures facilitates the conductivity of the material.Comment: 19 pages, 7 figures, Accepted in PR

Suppression of the metal-insulator transition by magnetic field in (Pr1−yYy)0.7Ca0.3CoO3 (y = 0.0625)

“…For the prototypical compound Pr 0.5 Ca 0.5 CoO 3 this valence shift was confirmed and determined quantitatively with the identification of the Pr 4þ -related Schottky peak in heat capacity measurements 12 and by X-ray absorption spectroscopy at the Pr L 3 edge. 13 Similar evidence was presented also for the Pr 0.7 Ca 0.3 CoO 3 systems doped by Y, [14][15][16] Sm, 17 and Tb. 18 Many studies have been done especially on the (Pr 1Ày Y y ) 0.7 Ca 0.3 CoO 3 system, which displays a MI-SS transition and partial Pr 3þ !…”

Tuning the Electronic Spin State of Catalysts by Strain Control for Highly Efficient Water Electrolysis

“…In order to further investigate the difference of electronic structures, X‐ray absorption spectroscopy of Co L‐edge was performed. In the spectra as shown in Figure a,b and Figure S6 (Supporting Information, the L 3 edge peak includes contributions from Co 2+ (Td) , Co 3+ (Oh, LS) , and Co 3+ (Oh, HS) (HS and LS stand for high spin and low spin, respectively) . We noticed a more intensive shoulder at around 777780 eV in PE‐ z ‐Co 3 O 4 as compared to that in Co 3 O 4 , which could be assigned to the increase of either the Co 2+ /Co 3+ ratio and/or high‐spin Co 3+ content.…”

“…Hence, increased Co 2+ /Co 3+ ratio would unlikely be the main cause for the more intensive shoulder observed in the Co L 3 edge spectrum of PE‐ z ‐Co 3 O 4 . The cobalt L 3 edge peak can be further deconvoluted to Co 2+ (Td) , Co 3+ (Oh, LS) , and Co 3+ (Oh, HS) (Figure a,b), which exhibits a much higher content of Co 3+ (Oh, HS) in PE‐ z ‐Co 3 O 4 as compared to that in Co 3 O 4 (conventional spinel). The higher content of Co 3+ (Oh, HS) in PE‐ z ‐Co 3 O 4 can be attributed to the structural distortion induced by surface ZIF‐67 transformation as ZIF‐67 has larger lattice constants than that of the substrate.…”

Deciphering the Interface of a High‐Voltage (5 V‐Class) Li‐Ion Battery Containing Additive‐Assisted Sulfolane‐Based Electrolyte

“…The bulk electronic structure of pristine and cycled LiNi 0.5 Mn 1.5 O 4 is revealed by soft X‐ray absorption spectroscopy (XAS) at the O‐K edge using a bulk sensitive fluorescence yield (FY) mode (Figure b). The O‐K XAS spectra of 3d transition metal (TM) oxides is also sensitive to the electronic structure of 3d TM ions . O‐K XAS spectra of SrMnO 3 and NiO is used as a Mn 4+ reference and a Ni 2+ reference, respectively.…”