Valence-state mixing and separation inSmBaFe2O5+w

Abstract

A mixed-valence state, formally denoted as Fe 2.5ϩ , is observed in the 300 K Mössbauer spectra of the most reduced samples of SmBaFe 2 O 5ϩw . Upon cooling below the Verwey-type transition temperature (T V Ϸ200 K), the component assigned to Fe 2.5ϩ separates into a high-spin Fe 3ϩ state and an Fe 2ϩ state with an unusually low internal field. The separation of the mixed-valence state at T V is also confirmed by magnetic susceptibility measurements and differential scanning calorimetry. A model is proposed which accounts for the variation of the amount of the mixed-valence state with the oxygen content parameter w.

Oxygen and cation ordered perovskite, Ba2Y2Mn4O11

“…BaYCo 2 O 5.0 (DP) [4]) and simultaneous valence-separation and charge-ordering transition (e.g. BaREFe 2 O 5.0 (DP) [5,6]). …”

Iron valence in double-perovskite (Ba,Sr,Ca)2FeMoO6: isovalent substitution effect

“…10 In terms of the magnitude of isomer shift a similar mixed-valence state had earlier been established by means of Mössbauer spectroscopy for the A-site ordered double-perovskite, SmBaFe 2 O 5+δ (δ ≈ 0). 11 In the case of SmBaFe 2 O 5+δ , the Fe II/III state separates upon cooling into equal amounts of divalent and trivalent iron at a Verweytype transition with T V ≈ 230 K, 11 while for Sr 2 FeMoO 6-w the mixed-valence state was confirmed to persist down to 5 K. 5 In terms of fine-tuning the charge distribution "isovalent" substitution at the A site is expected to provide us with interesting possibilities, as such a substitution keeps overall charge of the B cations constant, but is likely to influence the distribution of charge among the two cations. 3 (where R is a rare earth element and A an alkaline earth element) magnetoresistors with a simple perovskite structure it was found that with decreasing effective ionic radius at the (R,A)-cation site, the Curie temperature (T C ) decreased and the magnitude of the MR effect increased drastically.…”

Orbital occupancy evolution across spin- and charge-ordering transitions in YBaFe 2 O 5

“…12), typical also for other rare-earth variants of YBaFe 2 O 5 [13,[24][25][26], where the large dipolar field of the minority-spin electron in d xz nearly cancels the Fermi-contact field. This same electron makes the EFG large (Fig.…”

“…Since V zz of charge-ordered Fe 2+ is along b and the magnetic moments too [13,[24][25][26], their angle β = 0°, and η (Eq. (1)) is needed to evaluate eQV yy so that Eqs.…”