Spinel ferrites nanoparticles of the chemical formula CuAl_xFe_2-xO₄ (where x=0.0, 0.2, 0.4, and 0.6) have been synthesized using the citrate-nitrate auto-combustion technique. The crystal structure's properties of the synthesized nanoparticles have been determined through X-ray diffraction (XRD) and Fourier transform infrared (FTIR) analyses. The extracted XRD data has demonstrated that all samples have a single phase with no undesirable impurities or phases. The samples of (x=0.0 and x=0.2) have a tetragonal structure while the samples of (x=0.4, 0.6) have a cubic spinel structure. The average crystallite size of the nanoparticles is found to be in the accepted nano-size range. The lattice parameter behavior of the tetragonal and cubic samples correlates well with the Jahn-Teller effect and has a trend of increasing with the aluminum addition. Some parameters of crystal imperfections like dislocation density (δ) and strain (ε) have been found to increase with increasing the Al³⁺ concentration and to have an inverse behavior to that of the average crystallite size as expected. Also, the formation of CuAl ferrite samples has been further confirmed by the FTIR spectroscopy where the two prominent absorption bands of ferrites (υ₁ and υ₂) at approximately 592 cm^-1 and 410 cm^-1 have been clearly detected.