(Pseudo)binary Antimonides: Insights on Local Ordering and Effective Charge Configurations from ¹²¹Sb MAS NMR and Mössbauer Spectroscopies

Abstract

Binary antimonides of composition MSb (M = Al, Ga, In), RESb (RE = Sc, Y, La), CdSb, RE 4 Sb 3 (RE = Sc, La), and T 5 Sb 4 (T = Nb, Ta) as well as the pseudobinary solid solutions (La 0.25 M 0.75 ) 4 Sb 3 (M = Sr, Eu) were synthesized from the elements via arc-melting or induction heating and investigated by powder Xray diffraction, magnetic susceptibility, and solid-state 121 Sb MAS NMR as well as 121 Sb and 151 Eu Mossbauer spectroscopic studies. Besides CdSb, all compounds exhibit isolated antimony atoms (i.e., no Sb−Sb bonding), which formally carry a 3-fold negative charge, and only one single crystallographic Sb site is observed. While 121 Sb Mossbauer spectroscopic measurements of all X-ray pure phases were possible, not all of these compounds showed detectable 121 Sb MAS NMR signals due to Sb located on lower symmetric positions. For the cubic phases with high symmetry, a parameter was constructed on the basis of the 121 Sb MAS NMR data to describe the ratio between antimony positions with and without perfect cubic site symmetry, showing that structural disorder is present in all electron-precise compounds of this work. Magnetic measurements of (La 0.25 Eu 0.75 ) 4 Sb 3 (≡LaEu 3 Sb 3 ) further indicate divalent europium and antiferromagnetic ordering below T N = 5.4(1) K. The valence state was confirmed by 151 Eu Mossbauer spectroscopy. Thus, the gathered 121 Sb MAS NMR and 121 Sb and 151 Eu Mossbauer data were utilized to get a systematic overview regarding the effective charge configuration in terms of the 121 Sb chemical shift, formal valence states, and isomer shifts for Sb in the different structures of the studied series of compounds.

On the Discrepancy between Local and Average Structure in the Fast Na+ Ionic Conductor Na2.9Sb0.9W0.1S4

“…Comparing the 121 Sb NMR resonances at temperatures equidistant below the respective phase transitions, an average position of the NMR line shape singularities (quadrupolar splitting) can be estimated (Table S8), showing a higher quadrupolar coupling interaction for higher W substitution. Nevertheless, for both Na 2.95 Sb 0.95 W 0.05 S 4 and Na 2.9 Sb 0.9 W 0.1 S 4 (Figure c,d), a broadened 121 Sb resonance is still observed after the phase-transition temperature (Figure S6) to cubic symmetry observed from X-ray diffraction (Figure S4); the broadening of these 121 Sb NMR resonances cannot be fit assuming a single Gaussian or Lorentzian line shape, indicating contributions of 121 Sb species with stronger than just the average quadrupolar interaction. , Thus, the occurrence of a nonzero quadrupolar interaction above the phase transition for Na 2.95 Sb 0.95 W 0.05 S 4 and Na 2.9 Sb 0.9 W 0.1 S 4 shows that local distortions lead to a local tetragonal structure, in line with the observation of local tetragonal structure elements from the PDF analysis.…”

Mixed Valence and Superconductivity in Perovskite Antimonates

“…In this paper, we carefully examine the role of metal s electrons in the two quantum collective phenomena in recently synthesized Ba 1– x K x SbO 3 . For this purpose, we employ 121 Sb Mössbauer spectroscopy, − which allows us to directly probe Sb 5s electrons and thus reveal the mixed valence of Sb ions; Sb III and Sb V , with the nominal electron configurations of [Kr]­4d 10 5s 2 5p 0 and [Kr]­4d 10 5s 0 5p 0 , are well separated and can safely be distinguished in 121 Sb Mössbauer spectra as demonstrated for Sb III Sb V O 4 . , Combined with first-principles calculations, our results show that metal s electrons unambiguously contribute to the formation of the CDW order and superconductivity in the antimonates, which may also have implications on the general understanding of other high- T c superconductors including Ba 1– x K x BiO 3 .…”