Synthesis and study of Sr-substituted misfit layer sulfides

Abstract

Two series of [(Ln 1/3Sr 2/3S) 1.5] 1.15NbS 2 (1.5Q/1H) and (Ln 1− x Sr x S) 1+ y NbS 2 (1Q/1H) misfit layer sulfides have been synthesised and studied by X-ray powder and single crystal diffraction, EDX-analysis and magnetic measurements. For the early lanthanides (Ln = La, Ce) only the (Ln 1− x Sr x S) 1+ y NbS 2 ( x < 0.40–0.45, y = 0.15–0.17) compounds were formed whereas for late lanthanides (Ln = Pr, Nd, Sm, Gd–Er, Yb, Lu), and yttrium, both types of phases can be obtained. The crystal structure of (Pr 0.55Sr 0.45S) 1.15NbS 2 has been refined on the basis of X-ray single crystal data using the superspace approach. It consists of double layers [Pr 0.55Sr 0.45S] of NaCl-type (Q-part: a = 5.799(3) Å, b = 5.810(2) Å, c = 23.331(9) Å, z = 4) and NbS 2-sandwiches (H-part: a = 3.332(3) Å), z = 8, yielding a q-vector q = ( α 0 0), α = 0.74) alternating along the c-direction. The superspace group pair is Fm2 m ( α 0 0): Fm2 m ( α 0 0) (No. 42.7). The refinement converged to R w(obs) = 0.069. According to the structure refinement and EDX-analysis data in the [Pr 0.55Sr 0.45S]-slab almost half of the Pr-atoms are randomly replaced by Sr. The minimal formal value of charge transfer from the Q- to the H-part of the structure necessary to stabilise the misfit Nb-based layer sulfides has been estimated as about 0.6 ē per Nb atom.