Cation distributions in (Fe_{1 -z}Me_z)₃(PO₄)₂ graftonite-type solid solutions determined by Mössbauer spectroscopy

Abstract

Solid solutions of Me 3 (P0 4 ) 2 in Fe 3 (P0 4 ) 2 , with the graftonitetype structure, have been prepared and equilibrated at 1070 Κ (Me = Mg, Ca, Co, Ni, Zn, or Cd). The (Fe! _ 2 Afe z ) 3 (P0 4 ) 2 phases are isomorphous with Fe 3 (P0 4 ) 2 as well as with the mineral graftonite. Accurate unit cell dimensions (P2 1 /c) have been obtained from Guinier-Hägg photographic data. The unit cell volume is strongly correlated with the amount and size of the incorporated Me 2 + cation. Mössbauer spectroscopy ( 57 Fe) has been used to determine the cation distribution of Fe 2 + and Me 2 + between the three distinct cationic environments in the structure : one octahedron and two fivecoordinated polyhedra, all distorted. The order of preference for five-over six-coordination may be given as Zn 2+ > Fe 2 + , Mg 2+ , Co 2+ , Ni 2+ > Ca 2+ > Mn 2+ > Cd 2 + .

Crystallographic studies of olivine-related sarcopside-type solid solutions

“…Within each Ni ¡Me series, the smallest variation is noted for the monoclinic b axis. This is noteworthy, because in practically all {MEy _ z A/e z ) 3 (P0 4 ) 2 farringtonite and graftonite series, with the same space group symmetry as sarcopside, the largest change with composition was observed for the b axis (Nord and Stefanidis, 1981 ;Nord and Ericsson, 1982). {ME and Me are divalent metals).…”

“…Nord and Ericsson, 1982). Accurate X-ray powder difraction data of each sample were obtained at 295 Κ with an XDC-700 type focusing camera (monochromatized CrKal radiation, A = 2.28975 Â; KCl internal standard).…”

Classification of the minerals of the graftonite group

“…Steele et al (1991) and Wise et al (1990) refined the structures of Ca-free and Ca-rich beusite, respectively. Nord (1982) and Nord and Ericsson (1982 a ) looked at solid solution and Fe–Mn order in synthetic phases along the join graftonite–beusite, and Nord and Ericsson (1982 b ) looked at Fe 2+ –(Ca 2+ , Mg 2+ , Co 2+ , Ni 2+ , Zn 2+ , Cd 2+ ) order in synthetic graftonite-structure phases by Mössbauer spectroscopy.…”

Cation distribution studies of three (Ni, Mg) orthovanadates

“…Nord and Ericsson, 1982;Nord, 1983Nord, , 1984. In some cases it has been possible to establish simple empirical rules for cation distributions, for instance as regards five-and six-coordinated metal sites (Nord and Ericsson, 1985).…”