Representative diffraction patterns collected (a) 7 mm above the surface of the electrolyte, and (b) 3 mm below. The calculated diffraction pattern is shown in red, with the difference plot shown in grey. The absorption of lower-energy X-rays by the electrolyte is evident in (b). The data presented are from a stage in the reaction when the three phases Ti5O9, Ti6O11 and TiO2 were present at approximately 33 wt% each. Note that the two starred peaks in both (a) and (b) are due to lead K-fluorescence from the detector shielding and, as such, do not vary in intensity with time.