Abstract
Single crystals of a new twinned hexagonal perovskite compound Sr8Os6.3O24 have been synthesized, and structural and magnetic properties have been determined. The compound crystallizes in a hexagonal cell with lattice parameters a = 9.6988(3) Å and c = 18.1657(5) Å. The structure is an eight-layered hexagonal B-site deficient perovskite with the layer sequence (ccch)2 and represents the first example of a hexagonal structure among 5d oxides adopting a twin option. The sample shows spontaneous ferromagnetic magnetization below 430 K with a small saturation moment of 0.11 μB/Os ion. This is the highest Curie temperature (TC) reported for any bulk perovskite containing only 5d ions at the B site.
Highlights
Perovskites represent one of the robust and perhaps the most structurally variable classes of oxides.[1,2] The basic structure type ABO3 allows for replacements at A and B sites in different ratios and for a wide variety of stacking sequences of the AO3 dense packed layers, which results in a vast combinatorial diversity of individual configurations
In our quest to explore materials with possible high magnetic transition temperatures, we have discovered an interesting eight-layered twinned hexagonal perovskite that contains only Os at the B
Black single crystals (Figure 1) with hexagonal habit were obtained in the course of a solid-state reaction of SrO, SrO2, and OsO2 in a vacuum at 1073−1273 K
Summary
Perovskites represent one of the robust and perhaps the most structurally variable classes of oxides.[1,2] The basic structure type ABO3 allows for replacements at A and B sites in different ratios and for a wide variety of stacking sequences of the AO3 dense packed layers, which results in a vast combinatorial diversity of individual configurations. We consider our structure model presented here as an averaged one but quite approximate to the real structure, as few preceding reports of compounds with very similar structural features lend strong support to the validity of our structure model.[19−21,26] The resulting average composition Sr8Os6.3O24 is compliant with the other reported B-site deficient hexagonal perovskites of similar structures (Ba8Ga2.4Ta4.96O24 and Sr4Ru3.05O12 = Sr8Ru6.1O24) and is in excellent agreement with the EDX results.[20,26] These vacancies at the FSO sites help to reduce the electrostatic repulsion between the short Os−Os contacts, stabilizing the eight-layer twinned structure. Sr8Os6.3O24 has the highest ordering temperature (430 K) among bulk perovskite compounds containing only 5d metal at B sites It is the first example of an eightlayered hexagonal structure in 5d oxides adopting a twin option
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