Although I haven’t found any phase diagrams yet, I’ve been able to verify that OsS
2, OsSe
2, OsSb
2, and OsTe
2 have in fact been grown and are thought to be “line compounds,” i.e., they have compositions that are thought to be invariable. Unfortunately, Sb and Te cause interference problems near the Os Mα peak position, so OsS
2 and OsSe
2 are the only really viable choices among these. Also, OsP
4 is thought to be a line compound, though it must be grown in a sealed capsule/ampoule. Os borides and silicides have been grown as well, but their compositions have not been investigated thoroughly.
It’s possible that I could grow OsSe
2 using the technique described below, though I don’t know if I’d have to worry about generation of OsO
4 gas (starting with Os shot/lump, not powder/sponge). When growing selenides by this technique, it’s important to be mindful of the fact that Se boils at 685°C. Because Se is relatively volatile, I’ve simply saturated the system in the past (as this can be used ensure production of the desired line compound).
https://probesoftware.com/smf/index.php?topic=1310.0P.S. Nominal OsAs
2 has been grown, but it is known to have variable composition that ranges roughly between OsAs
1.8 and OsAs
2.2.
P.P.S. Stoichiometric OsSe
2 contains 54.64 wt% Os and 45.36 wt% Se.
P.P.P.S. In my personal experience, I've most commonly encountered wt% (or greater) Os in laurite, nominally RuS
2 and the only(?) commonly occurring Ru-rich PGM. It forms a solid solution with erlichmanite (OsS
2). For these reasons alone, a good synthetic erlichmanite standard would be good to have (along with a synthetic laurite standard). But OsSe
2 might be good enough.
P.P.P.P.S. I'm not tremendously worried about generation of OsO
4 gas when using the above technique because 1) the amount of Os is very small and its surface area relative to volume will be small (shot/lump, not powder/sponge), 2) the Os will be fully immersed in Se liquid at 221°C, and 3) all reactants will be encapsulated by B
2O
3 liquid at about 450°C. Thus, significant interaction with the atmosphere will end within a few hours of turning on the furnace; the reactants will probably need to sit in the furnace for at least a week at ~600°C to ensure complete reaction of the metal. Also, OsO
4 is supposed to have a distinctive garlic-like odor. I'm happy for input from anyone on the safety issues regarding working with osmium.