Abstract
The ratios between the number of total metal atoms and oxygen atoms were found to be close to 1:2 for the several synthetic samarskites having various relative amounts of metal atoms. Samarskite was also synthesized using starting materials in the ternary Y–Fe–Nb–O system. Analysis of this material gave a formula: YFe2Nb5O16, which was the same bulk composition as that of the starting reagents. The synthesized and recrystallized natural samarskites changed into mixtures of mostly three to four compounds when heated in air. They changed into the high temperature structural form of samarskite when heated at 950–1200°C in a reducing atmosphere. Refinement of cell parameters for the high temperature form of a samarskite from Kawabe, Japan yielded: a = 5.642(7)Å, b = 9.914(8)Å, c = 5.229(3)Å, and β = 93.8(7)°.
On the basis of the experimental results obtained in the present and previous studies, samarskite is proposed to be a mineral with α-PbO2 structure, covering a wide range of chemical compositions and occurring as either partially disordered A3B5O16 or completely disordered M8O16. A diagram showing the structural relation to related minerals columbite, ixiolite, wolframite, and others is presented.