Crystal Growth of a New 8H Perovskite Sr₈Os_6.3O₂₄ Exhibiting High T_C Ferromagnetism

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.

Buckled Honeycomb Lattice Compound Sr3CaOs2O9 Exhibiting Antiferromagnetism above Room Temperature

“…This kind of corner shared-buckled honeycomb lattice has been observed before only in the isostructural compounds Sr 3 Ca­(Ru/Ir) 2 O 9 . , Moreover, a honeycomb pattern of Os is even rarer and in fact has only been reported previously in Li 2.15 Os 0.85 O 3 (although, edge-shared) . Bond distances between Os and O are in a range of 1.88–2.06 Å and agree well with those reported in the literature. ,− However, the Ca–O distances in Sr 3 CaOs 2 O 9 appear to be slightly shorter (2.19–2.24 Å) than expected, as far as their ionic radii are concerned . These short Ca–O distances comply with a small degree of an anti-site disorder at the Ca and Os positions.…”

“…In continuation to our expedition to find compounds containing osmium and featuring magnetic ordering transitions at high temperatures, − we report the new compound Sr 3 CaOs 2 O 9 crystallizing in a conventional monoclinic triple-perovskite structure. Sr 3 CaOs 2 O 9 orders antiferromagnetically below T N ≈ 385 K. The previously known isostructural compound Sr 3 CaRu 2 O 9 , whose magnetic properties were hitherto unreported, has also been studied using magnetization and electrical resistivity.…”

New Sr9Os5O23, Made Up of Quasi 1D and 2D Fragments of the Perovskite Structure

“…Figure shows the connectivity and bond distances within the Os octahedra. The spread of bond distances in the Os2 octahedra are fairly narrow and do not show much deviation (1.95 to 1.99 Å) and are consistent with the bond distances reported for Os 5+/6+ . ,− ,, However, the bond distances in Os1 and Os3 show much larger spread (1.85 to 2.1 Å), which can be attributed to the different crystal chemical functions of the respective oxygen atoms: The longer bonds in Os1 and Os3 octahedra are formed with oxygen atoms bridging the neighboring Os octahedra, while the shorter ones contain oxygen atoms bridging to the neighboring Sr atoms.…”

“…Heating stoichiometric mixtures of SrO 2 , SrO, and OsO 2 between 1073 and 1273 K resulted in a mixture of the Sr 9 Os 5 O 23 phase (∼30%) and the previously reported Sr 5 Os 3 O 13 (∼70%) . Crystal growth using the approach reported for synthesis of Sr 5 Os 3 O 13 and Sr 8 Os 6.3 O 13 also resulted in mixtures of several crystalline phases including the target compound, Sr 5 Os 3 O 13 (elongated plates), Sr 3 OsO 6 (powder), and hexagonal crystals of a yet unreported 10H perovskite-type phase, possibly Sr 7 Os 3 O 15 (under investigation). …”

“…Ternary and quaternary osmates continue to attract distinct attention for their pertinent physical properties by virtue of manifestations of spin–orbit coupling (SOC), Hund’s coupling, and Coulomb correlation operating on similar energy scales. Respective observations have revealed, e.g., reduced effective paramagnetic moments, − temperature dependent charge order, high magnetic ordering temperature, − or unusual S = 0 state of Os 6+ . , …”