Magnetic Investigations and 151Eu Mössbauer Spectroscopy of MYbSi4N7 with M = Sr, Ba, Eu

Abstract

AbstractThe isotypic nitridosilicates MYb[Si4N7] (M = Sr, Ba, Eu) were obtained by the reaction of the respective metals with Si(NH)2 in a radiofrequency furnace below 1600 °C. On the basis of powder diffraction data of MYb[Si4N7] Rietveld refinements of the lattice constants were performed; these confirmed the previously published single‐crystal data. The compounds contain a condensed network of corner‐sharing [N(SiN3)4] units. The central nitrogen thus exhibits ammonium character. Magnetic susceptibility measurements of MYb[Si4N7] (M = Sr, Ba, Eu) show paramagnetic behavior with experimental magnetic moments of 3.03(2), (Sr), 2.73(2) (Ba), and 9.17(2) (Eu) μB per formula unit. In EuYbSi4N7 the europium and ytterbium atoms are in stable divalent and trivalent states, respectively. According to the non‐magnetic character of the alkaline earth cations, ytterbium has to be in an intermediate valence state YbIII‐x in the strontium and barium compound. Consequently, either a partial exchange N3—/O2— resulting in compositions MYbIII‐x[Si4N7—xOx] or an introduction of anion defects according to MYbIII‐x[Si4N7—x/3□x/3] has to be assumed. The phase width 0 ≤ x ≤ 0.4 was estimated according to the magnetic measurements. 151Eu Mössbauer spectra of EuYb[Si4N7] at 78 K show a single signal at an isomer shift of δ = —12.83(3) mm s—1 subject to quadrupole splitting of ΔEQ = 5.7(8) mm s—1, compatible with purely divalent europium.