I have prepared Zn doped TiO2 by microwave assisted method and surprisingly we got XRD shift to higher angle. Further increase the concentration of Zn the intensity of the peak get decreased.
Zn doping has probably distorted the TiO2 lattice to make the crystal planes (I do not know which peak you are talking about so I am making a general observation) come closer. Higher doping is probably amorphizing the TiO2. However, please cross-check with HRTEM. Maybe interesting.
There hase been another thread recently on a similar question: https://www.researchgate.net/post/Is_a_difference_of_1_degree_on_XRD_results_between_sputtered_target_and_thin_film_significant