K2NaOsO5.5 and K3NaOs2O9: The first osmium perovskites containing alkali cations at the “A” site

High-Temperature Ferrimagnetism with Large Coercivity and Exchange Bias in the Partially Ordered 3d/5d Hexagonal Perovskite Ba2Fe1.12Os0.88O6

“…As the Mössbauer spectra show only Fe 3+ signals (see below), it is expected that the non-stoichiometry leads to a minority Os 6+ component in addition to the majority Os 5+ component. Os2O9 dimeric units such as K3NaOs2O9 and Ba3NaOs2O9 41,42 and were attributed to displacement of the high-valent osmium ions from the center positions. The mean value of the bond distances of Fe4/Os4−O1 and Fe4/Os4−O2 is 1.987 Å, which is close to the values obtained for the other three metal sites.…”

Structure and Magnetic Properties of Sr2NaOsO6

“…The Os–O bond lengths lie in the range 1.79 to 1.83 Å which is the expected distance for heptavalent Os in VI coordination with oxygen. [ 15,16,18–20 ] Till date, there are but very few well characterized Os(VII) oxides known, Na 3 OsO 5 , [ 18 ] AOsO 4 (A = Na, K, Rb), [ 19 ] K 3 NaOs 2 O 9 , [ 20 ] and only a few of them belong to the perovskite family [A 2 (Li,Na)OsO 6 (A = Ba, Sr) [ 13,21 ] ]. Bond valence sum (BVS) [ 22 ] calculated for the three cations Sr +2 , Na +1 and Os +7 is 1.87, 1.38 and 7.98, respectively.…”

“…We presume this suppression of moment is due to the larger strong spin‐orbit coupling and greater crystal field effects as also seen in most of the osmium containing perovskites. [ 13,20,21 ] A negative value of the Weiss constant indicates predominant antiferromagnetic interactions among the Os ions. We assign the steep increase in χ below ca.…”

“…a strongly reduced paramagnetic moment and AFM exchange coupling, appear to be common features of osmium(VII) oxides, in particular for ternary phases adopting the double perovskite‐type of structure. [ 13,20,21 ] While relativistic spin‐orbit coupling appears to be accountable for the reduced (local) paramagnetic moment, the different individual manifestations of AFM exchange coupling may be related to geometric frustration inherent to the basically fcc arrangement of Os in B‐site ordered double perovskites.…”

Crystal structures of the triple perovskites Ba2K2Te2O9 and Ba2KNaTe2O9, and redetermination of the double perovskite Ba2CaTeO6

“…Such a compression has also been reported for other 6H-BaTiO 3 -type structures containing sodium. For example, the Na-O distance in K 3 NaOs 2 O 9 has nearly the same value [2.313 (6) Å ; Mogare et al, 2012] but is reported to be significantly shorter in Ba 3 NaRuIrO 9 [2.058 (9) Å ; Lufaso & zur Loye, 2005b].…”