(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, RE4Sb3 (RE = Sc, La), and T5Sb4 (T = Nb, Ta) as well as the pseudobinary solid solutions (La0.25M0.75)4Sb3 (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 121Sb MAS NMR as well as 121Sb and 151Eu Mössbauer 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 121Sb Mössbauer spectroscopic measurements of all X-ray pure phases were possible, not all of these compounds showed detectable 121Sb 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 121Sb 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 (La0.25Eu0.75)4Sb3 (≡LaEu3Sb3) further indicate divalent europium and antiferromagnetic ordering below TN = 5.4(1) K. The valence state was confirmed by 151Eu Mössbauer spectroscopy. Thus, the gathered 121Sb MAS NMR and 121Sb and 151Eu Mössbauer data were utilized to get a systematic overview regarding the effective charge configuration in terms of the 121Sb chemical shift, formal valence states, and isomer shifts for Sb in the different structures of the studied series of compounds.