Broad X-ray diffraction peaks means that the atoms are not at a precise position (crystallographic site) but around this value. May be you need annealed your sample to obtain better thermal equilibria.

Best regards,

Pedro

The broaden of XRD peaks indicates that the particle size you are preparing are very small on the one hand, it is also due to the formation of the solid solutions in your case. You can calculate the particle size using Scherrer equation and compare it to direct measured value from TEM. 

For details, you can read:

HP Klug and LE Alexander, X-Ray Diffraction Procedures for Polycrystalline and Amorphous Materials, 2nd edition, John Wiley & Sons, 1974.

Chapter 9: Crystallite Size and Lattice Strains from Line Broadening