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A fact from Samarium monochalcogenides appeared on Wikipedia's Main Page in the Did you know column on 6 December 2010 (check views). The text of the entry was as follows:
Did you know... that samarium monosulfide changes color from black to golden when scratched?
Truly fascinating! I would have expected defect structures, not a regular structure like NaCl. Two questions arise. Is the sub-oxide SmO known and if so, what is the structure? The +2 oxidation state is well-known for Eu. How does EuS compare with SmS? Petergans (talk) 11:02, 6 December 2010 (UTC)[reply]
There is one report of SmO0.656doi:10.1002/pssa.2210140124 (Pearson symbol hR159, space group R3m), but not for Eu. Non-stoichiometric crystalline structures SmaXb, with b/a from almost 0.5 to 3 are rather common for Sm compounds. Several were reported for Sm bromides and fluorides, but none for Sm chlorides - my wild guess is they all exist, but either not published or not in my database. Materialscientist (talk) 11:20, 6 December 2010 (UTC)[reply]
