Effect of transition-metal-ion doping on high temperature thermal expansion of 3:2 mullite -: An in situ, high temperature, synchrotron diffraction study

The effect of Ti4+, Cr3+ or Ga3+ doping on thermal expansion of 3:2 mullite was examined from 20 degrees C to 1400 degrees C by high temperature XRD using synchrotron radiation. The room temperature mullite lattice expanded with metal-ion incorporation and the change in the b-axis was larger than that along the a-axis (Delta b > Delta a) for all ion types. Upon beating, the largest elongation was along the b-axis (Delta b/b(RT)) and was similar to that in the pure mullite (similar to 0.5%). Least expansion was observed along the a-axis (0.28% <= Delta a/a(RT) <= 0.41%). The thermal expansion of mullite was not constant in the temperature range from 20 degrees C to 1400 degrees C, and had a linear dependence on temperature (alpha(T) =A(0) +A(1)Delta T). The alpha(mean) values increased with temperature (20 degrees C <= T <= 1000 degrees C), but were always within 3.0-6.7. Cr3+ and Ga3+ dopino decreased the anisotropy in mullite lattice expansion, however, Ti4+ doping showed a sharp increase. Trends associated with type and the quantity of dopant are discussed. (c) 2007 Elsevier Ltd. All rights reserved.