Anders G. Nord

The cation distribution between five- and six-coordinated sites in some (Mg,Me)3(PO4)2) solid solutions

Abstract Approximate homogeneity ranges at about 1073 K have been determined for some (Mg, Me )3(PO4)2 solid solutions. X-ray powder diffraction data are given and the observed changes in unit cell dimensions are discussed. The Mg3(PO4)2 structure, isotypic with γ-Zn3(PO4)2, contains five- and six-coordinated cation sites, M1 and M2 respectively. The M1 site preference order is Zn2+ > Co2+ > Fe2+ > Mg2+ > Mn2+.

Crystal chemistry of γ-(Zn, Me)3(PO4)2 solid solutions

Abstract A number of γ-(Zn, Me ) 3 (PO 4 ) 2 solid solutions with the “γ-Zn 3 (PO 4 ) 2 ” structure have been prepared and equilibrated at about 1070 K ( Me = Mg, Mn, Fe, Co, Ni, Cu, and Cd ). Approximate homogeneity ranges are given. The monoclinic unit cell dimensions have been accurately determined from Guinier-Hagg photographs. The structure contains five- and six-coordinated cations. Correlations between homogeneity ranges, unit cell dimensions, cation radii and cation distributions are pointed out, and the phases are also compared with isotypic (Mg, Me 3 (PO 4 ) 2 and (Co, Me ) 3 (PO 4 ) 2 solid solutions.

The crystal structure of iron(II) diphosphate, Fe2P2O7

The preparation of Fe2P207 is described, with a technique to produce single crystals. The triclinic ( P I ) unit cell has the dimensions a = 5.517(2), b = 5.255(2), c = 4.488(l)Ä, α = 98.73(2)°, 0 = 98.33(4)°, γ = 103.81(2)°, V= 122.6(2)Ä (Ζ = 1). The formula weight is 285.64atomic units, and the calculated density is 3.868 g · cm 3 . The crystal structure has been determined by direct methods and refined to RF = 0.049 on the basis of 722 independent X-ray single-crystal reflections (PW1100 diffractometer data). The building elements of the structure are two distinct FeOe octahedra in combination with diphosphate ions. Each FeO e octahedron shares three edges with octahedra of the other type. The FeO e octahedra are distorted, with F e Ο distances in the ranges 1.98 — 2.44A (mean: 2.16Ä) and 2.04 —2.63 A (mean: 2.21 A). The diphosphate anion h a s a P — Ο — Ρ angle of 153°. The P 0 4 tetrahedra are also distorted, with a Ρ—Ο grand mean distance of 1.536 A.

Crystal chemistry of α-(Zn,M)2V2O7 solid solutions correlation between preference for five-coordination and extension of solid solubility

Solid solutions of M2V2O7 in α-Zn2V2O7 have been prepared and equilibrated at 600°C (M = Mg, Ca, Mn, Co, Ni, Cu, Zn, and Cd). The crystal structure of α-Zn2V2O7 contains only one type of metal site, which is five-coordinated by a somewhat distorted trigonal bipyramid ZnO5 (Gopal & Calvo, 1973). The solubility range is largest for Cu2+ and Co2+ which can substitute for about 35% of the zinc atoms. The cations can be arranged in the following sequence with respect to their solubility in α-Zn2V2O7, which accords well with these ions preference for five-coordination: nZn2+>> (Cu2+,Co2+) > Mg2+ >(Ni2+, Mn2+) > Cd2+

Graftonite-type and graftonite-related (Mn1−zMez)3(PO4)2 solid solutions

Abstract A number of solid solutions of Me 3 (PO 4 ) 2 in Mn 3 (PO 4 ) 2 have been prepared and equilibrated at 1070 K. Most of the respective ( Mn 1− z Me z ) 3 ( PO 4 ) 2 phases crystallize with the graftonite structure ( Me = Mg, Fe, Co, Ni, Cu, Zn, or Ca ), but the (Mn, Cd) 3 (PO 4 ) 2 solid solutions are isomorphous with β′-Mn 3 (PO 4 ) 2 . Approximate homogeneity ranges are given. The monoclinic unit cell dimensions have been accurately determined from Guinier-Hagg photographs, and complete X-ray powder diffraction film-scanner data are given for β′-Mn 3 (PO 4 ) 2 . Correlations between homogeneity ranges, unit cell dimensions and cation radii are pointed out, and the manganese-containing graftonite phases are also compared with the isotypic ( Fe 1− z Me z ) 3 ( PO 4 ) 2 solid solutions.

Strong Zn2+/Mn2+ cation ordering among five- and six-coordinated sites in γ-(Zn0.75Mn0.25)3(PO4)2

Abstract The solid solution γ-(Zn0.75Mn0.25)3(PO4)2 has been studied utilizing neutron powder diffraction data. The monoclinic (P21/n) structure has been refined by means of the Rietveld full-profile technique (R1= 0.051, Rp, = 0.057). The results clearly show that the cations are strongly ordered; Zn2+ at the five-, and Mn2+ at the six-coordinated sites. The “ZnO5” polyhedra are somewhat distorted trigonal bipyramids, while the “MnO6” octahedra are fairly regular.

Crystallographic studies of olivine-related sarcopside-type solid solutions

Etude, par diffraction des neutrons et des rayons X, de la structure cristalline des solutions solides (Ni 1−z Me z ) 3 (PO 4 ) 2 de type sarcopside (P2 1 /a (Me=Mg, Mn, Co, Fe, Cu et Zn). Les volumes de maille de ces phases dependent de la taille et teneur de lion Me. Determination de la distribution des cations entre les 2 sites octaedriques M 1 et M 2 , distribution controlee par lenergie du champ cristallin (effet de taille mineur)

Neutron diffraction studies of NiCoP4O12 and NiZnP4O12

The title compounds belong to a group of isostructural M2P4O12 tetrametaphosphates with monoclinic (C2/c) symmetry. The two structures have been profile-refined by means of the Rietveld technique on the basis of neutron powder diffraction data. The three-dimensional framework is built up of tetrametaphosphate anions and two distinct metal-oxygen octahedra, (M1)O6 and (M2)O6. The latter octahedron is somewhat larger and more distorted than (M1)O6. The results show that in both solid solutions nickel preferentially enters the M1 sites, a tendency also observed in olivine and sarcopside, which contain MO6 octahedra similar in shape and symmetry to those in M2P4O12.

Crystallographic studies of some olivine-related (Ni, Mg)3(PO4)2 solid solutions

Olivine-related (Ni, Mg)3(PO4)2 solid solutions were prepared and equilibrated at 1070 K. Accurate monoclinic unit cell dimensions were determined from Guinier-Hägg photographic data. Structural refinements based on the X-ray profile-fitting technique after Rietveld were carried out for pure nickel (II) orthophosphate and for three Ni/Mg solid solutions. (Ni1-xMgx)3(PO4)2 phases with 0.40≦x≦0.60 are probably isostructural with Ni3(PO4)2 (P21/a) while phases with low magnesium contents (<27 atom % Mg) deviate structurally from Ni3(PO4)2. The results also show that Ni2+ is partially ordered at the octahedralM(1) sites, withKD(Ni, Mg)=4.0±0.2