A high-resolution synchrotron powder diffraction study of substituted gallium ferrites using flat-plate fixed angle of incidence geometry on beamline I11 at Diamond

摘要

Very high resolution powder diffraction structural studies of the potentially room temperature multiferroic Ga _(2-x) Fe _xO _3 solid solution series (x = 0.7-1.3, 0.1 steps) have been undertaken using a fixed angle of incidence geometry. The applied absorption correction was seen to improve the goodness of fit (χ ~2) of the Rietveld refinements from an average of 1.41 to 1.06. The correction also resulted in an increased mean isotropic displacement parameter from 0.5 to 0.65. The mean difference in the fractional coordinates of the atoms between the refined models from the corrected and uncorrected data was 0.0007 ?, compared with the mean fractional coordinate error of 0.0003 ?. It is concluded that the final crystal structures refined from the corrected and uncorrected data are not significantly different. The number of reflections in each data set was over 2700, and the average peak half-width was 0.018° with the data binned in 4 millidegree steps. The data quality allowed bond length and angle determinations of sufficiently high accuracy to measure significant metal site distortions to an average precision of 0.007 ?. A lattice parameter nonlinearity was observed on either side of the x = 1 composition; this was attributed to local distortions, primarily of the Fe1 and Ga2 sites.