Abstract
A polycrystalline sample of Ba3Fe2TeO9 having the 6H perovskite structure has been prepared in a solid-state reaction and studied by a combination of electron microscopy, Mössbauer spectroscopy, magnetometry, X-ray diffraction and neutron diffraction. Partial ordering of Fe3+ and Te6+ cations occurs over the six-coordinate sites; the corner-sharing octahedra are predominantly occupied by the former and the face-sharing octahedra by a 1:1 mixture of the two. On cooling through the temperature range 18 < T/K < 295 an increasing number of spins join an antiferromagnetic backbone running through the structure while the remainder show complex relaxation effects. At 3K an antiferromagnetic phase and a spin glass coexist.
Highlights
The structure of a cubic perovskite ABO3 can be considered to consist of pseudo-close-packed AO3 layers stacked in a cubic-close-packed sequence, with B cations occupying six-coordinate interstitial sites between the layers; the layers lie perpendicular to the [111] axis of the cubic unit cell
One significant consequence of the change in stacking sequence is that the connectivity between BO6 octahedra switches from vertex-sharing to facesharing, introducing short contacts between B cations
The X-ray powder diffraction (XRPD) pattern of the reaction product suggested that the synthesis had produced a phase-pure 6H hexagonal perovskite
Summary
The structure of a cubic perovskite ABO3 can be considered to consist of pseudo-close-packed AO3 layers stacked in a cubic-close-packed (ccp) sequence, with B cations occupying six-coordinate interstitial sites between the layers; the layers lie perpendicular to the [111] axis of the cubic unit cell. The six-coordinate sites in many perovskites, both pseudo-cubic and hexagonal, are occupied by more than one species of cation, leading to the use of formulae of the form A2BB'O6 and A3B2B'O9 in cases where the distribution of cations is non-random and a particular cation species has a preference for one of the crystallographically-distinct sites. This cation ordering can have a marked effect on the physical properties of the compound
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