Structural and magnetic study of Yb³⁺ in the perovskites Sr₂YbMO₆ (M=Nb, Ta, Sb)

The compounds Sr₂YbNbO₆, Sr₂YbTaO₆ and Sr₂YbSbO₆ have been prepared using solid state methods by heating pelleted reagents in air at temperatures up to 1400 °C. Rietveld refinement against room temperature neutron powder diffraction data show that all three compounds crystallise with a cation-ordered variant of the perovskite structure in the P2₁/n space group. Complete cation ordering occurs between M⁵⁺ and Yb³⁺ over two octahedrally-coordinated sites in the structure and all compounds are stoichiometric in oxygen. The Sb–O bond lengths are similar to related perovskite compounds but differ slightly from those indicated by bond valence sums. Magnetic susceptibility data resemble Curie–Weiss paramagnetic behaviour, but can be better understood as arising from the effect of the octahedral crystal field on the ²F_5/2 ground state of Yb³⁺ leading to a temperature dependent magnetic moment on this ion below 100 K. - Graphical abstract: The magnetic susceptibility of the face-centred cubic Yb³⁺ lattice is dominated by the temperature dependent single-ion moment below 100 K. - Highlights: • Cation-ordered perovskites are studied using neutron diffraction and magnetometry. • Yb³⁺ cations form a pseudo face centred cubic lattice in a distorted structure. • Sb⁵⁺ cation is slightly overbonded as observed in related perovskites. • Crystal field splitting of 4f¹³ Yb³⁺ giving a temperature dependent moment. • Magnetic susceptibility reproduces theoretical predictions below 100 K