X-RAY RIETVELD ANALYSIS OF THE 6H SOLID SOLUTION BaTi_l-xFe_x0_3-z. R.S. Roth and T.A. Vanderah, NIST Ceramics Division, Gaithersburg, Maryland, and I.E. Grey and L. Cranswick, CSIRO Division of Minerals, PO Box 124, Port Melbourne, Australia

BaTiO₃ is stabilised in the 6-layer hexagonal structure by the addition of iron at x ~ 0.05 in BaTi_1-xFe_xO_3-z. This structure is stable to a composition with x ~ 0.85. Specimens equilibrated at 1250 - 1270deg.C followed by step cooling to 750deg.C show a maximum in the plot of the cell parameter c versus x (Vanderah, Loezos & Roth, 1996).

Rietveld analysis of x-ray powder patterns of nine compositions spanning this series revealed interesting details of the structure and chemistry of these specimens. The use of a variable counting time data collection strategy (Madsen and Hill, 1994) was found to give more consistent refined structural parameters, particularly thermal parameters and site occupancies.

With increasing iron content of the solid solution phases, progressively poorer fits to the powder patterns were obtained for the step-cooled samples. This led to studies on the effect of quenching and low temperature annealing on the bulk structure properties, the results of which will be reported.

T.A. Vanderah, J.M. Loezos and R.S. Roth, J. Solid State Chem. (1996)

(in press)

I.C. Madsen and R.J. Hill, J.Appl. Cryst. (1994). 27, 385-392