High-pressure synthesis, crystal structure, and magnetic properties of KSbO₃-type 5doxides K_0.84OsO₃and Bi_2.93Os₃O₁₁

5d Solid-state oxides K_0.84OsO₃ (Os^5.16+; 5d^2.84) and Bi_2.93Os₃O₁₁ (Os^4.40+; 5d^3.60) were synthesized under high-pressure and high-temperature conditions (6 GPa and 1500-1700 °C). Their crystal structures were determined by synchrotron x-ray diffraction and their 5d electronic properties and tunnel-like structure motifs were investigated. A KSbO₃-type structure with a space group of Im-3 and Pn-3 was determined for K_0.84OsO₃ and Bi_2.93Os₃O₁₁, respectively. The magnetic and electronic transport properties of the polycrystalline compounds were compared with those obtained theoretically. It was revealed that the 5d tunnel-like structures are paramagnetic with metallic charge conduction at temperatures above 2 K. This was similar to what was observed for structurally relevant 5d oxides, including Bi₃Re₃O₁₁ (Re^4.33+; 5d^2.66) and Ba₂Ir₃O₉ (Ir^4.66+; 5d^4.33). The absence of long-range magnetic order seems to be common among 5d KSbO₃-like oxides, regardless of the number of 5d electrons (between 2.6 and 4.3 per 5d atom).