The chemistry of your sample has changed. Have you analyzed the peak for its components ... Ti, TiO2, and TiOx? What happens to the relative amounts of those components? What happens to the ratio of Ti / O(TiO2 + TiOx) ? Your next line of investigation should be to answer these type of questions.
Otherwise, I am unclear about what you ask. Are you confused about the connection between peak position in XPS and the chemistry of the sample? If so, I would suggest that you need to read some background books about XPS. Alternatively, are you curious about the fundamental processes that might cause the chemistry to change? If so, I would suggest that you need to do some detailed literature search, for example on such combined keywords as XPS + TiO2 + calcination.