Identification of Various Coexisting Phases in Superconducting and Non-superconducting Samples of Rb sub( x)Fe sub( 2-y)Se sub( 2)

...Rb NMR, muon spin relaxation (...SR), and neutron diffraction studies have been carried out to investigate how the superconducting (SC) fraction is determined in Rb...Fe...Se... samples. We observe several phases with different compositions, crystal structures, and magnetic properties of each sample. Samples containing a phase with superconductivity (SC phase) are separated into two phases, an antiferromagnetic (AFM) phase with the block-type antiferromagnetism (AFM1 phase; space group I4/m, Neel temperature T... ~ 550 K) and the SC phase (I4/mmm, SC transition temperature T... ~ 30 K). This SC phase has a very small amount of Fe vacancies, if any. In samples having no SC phase, besides the AFM1 phase, there are two other phases, an AFM phase (AFM2 phase; Pmna, T... ~ 150 K) and a phase with an appreciable amount of Fe vacancy (I4/mmm; non-SC phase). Thus, the presence of the coexisting phases is an origin of the complicated physical behavior dependent on the \((x,y)\) values observed in the Rb...Fe...Ses... samples. (ProQuest: ... denotes formulae/symbols omitted.)