Refinement of the crystal structural parameters of the intermediate phase of h-BaTiO₃ using convergent-beam electron diffraction

Crystal structural parameters (21 positional parameters and nine isotropic Debye-Waller factors) of the intermediate phase of hexagonal barium titanate (h-BaTiO) have been refined by a structure analysis method using convergent-beam electron diffraction (CBED); this method was developed by Tsuda & Tanaka [Acta Cryst. (1999), A55, 939-954]. In order to perform the analysis, a parallel computation using a computer cluster composed of 16 connected Pentium 4 PCs was introduced. A function of parallel computation has been implemented in our analysis software, MBFIT, with the aid of the Message Passing Interface (MPI). Parallel computation enabled the present refinement to be conducted using a [001] CBED pattern and a [010] CBED pattern simultaneously. Reliable errors for the refined structural parameters have been obtained from the analyses of four independent experimental data sets instead of using the errors obtained by the error-propagation rule of least-squares fitting. The parameters obtained have been found to agree well with those determined by a neutron Rietveld analysis.