Abstract. Methods have been developed to facilitate the data analysis of multiple two-dimensional powder diffraction images. These include, among others, automatic detection and calibration of Debye–Scherrer ellipses using pattern recognition techniques, and signal filtering employing established statistical procedures like fractile statistics.

All algorithms are implemented in the freely available program package Powder3D developed for the evaluation and graphical presentation of large powder diffraction data sets.

As a case study, we report the pressure dependence of the crystal structure of iron antimony oxide FeSb₂O₄ (p≤21 GPa, T = 298 K) using high-resolution angle dispersive x-ray powder diffraction. FeSb₂O₄ shows two phase transitions in the measured pressure range. The crystal structures of all modifications consist of frameworks of Fe²⁺O₆ octahedra and irregular Sb³⁺O₄ polyhedra. At ambient conditions, FeSb₂O₄ crystallizes in space group P4₂/mbc (phase I). Between p = 3.2 GPa and 4.1 GPa it exhibits a displacive second order phase transition to a structure of space group P 2₁/c (phase II, a = 5.7792(4) Å, b = 8.3134(9) Å, c = 8.4545(11) Å, β = 91.879(10)°, at p = 4.2 GPa). A second phase transition occurs between p = 6.4 GPa and 7.4 GPa to a structure of space group P4₂/m (phase III, a = 7.8498(4) Å, c = 5.7452(5) Å, at p = 10.5 GPa). A nonlinear compression behaviour over the entire pressure range is observed, which can be described by three Vinet equations in the ranges from p = 0.52 GPa to p = 3.12 GPa, p = 4.2 GPa to p = 6.3 GPa and from p = 7.5 GPa to p = 19.8 GPa. The extrapolated bulk moduli of the high-pressure phases were determined to K₀ = 49(2) GPa for phase I, K₀ = 27(3) GPa for phase II and K₀ = 45(2) GPa for phase III. The crystal structures of all phases are refined against x-ray powder data measured at several pressures between p = 0.52 GPa, and 10.5 GPa.

Print publication: Issue 25 (28 June 2006)
Received 19 December 2005, in final form 9 February 2006
Published 8 June 2006