Modeling of X-ray Diffraction Line Broadening with the Voigt Function: Applications to High-(T sub c) Superconductors.

摘要

A method to analyze powder-diffraction line broadening is proposed and applied to some novel high-T(c) superconductors. Assuming that both size-broadened and strain-broadened profiles of the pure-specimen profile are described with a Voigt function, it is shown that the analysis of Fourier coefficients leads to the Warren-Averbach method of separation of size and strain contributions. The method was applied to two cubic structures with average volume-weighted domain sizes up to 3600 A, as well as to tetragonal and orthorhombic (La-Sr)2CuOr, which exhibit weak line broadenings and highly overlapping reflections. Comparison with the integral-breadth methods is given. Reliability of the method is discussed in the case of a cluster of the overlapping peaks. The analysis of La2CuO4 and La(1.85)M(0.15)CuO4 (M = Ca, Ba, Sr) high-T(c) superconductors showed that microstrains and incoherently diffracting domain sizes are highly anisotropic. In the superconductors, stacking-fault probability increases with increasing T(c); microstrain decreases. In La2CuO4, different broadening of (h00) and (0k0) reflections is not caused by stacking faults; it might arise from lower crystallographic symmetry.