Influence of the Synthesis Route in Obtaining the Cubic or Tetragonal Copper Ferrite Phases

In this work, magnetic copper ferrite nanoparticles are synthesized by polymer-assisted sol–gel and coprecipitation methods. The obtained purity and particle size reach values of 96% and 94 nm, respectively. Evident differences in the crystal structure have been found in the synthesized nanoparticles. A tetragonal structure is formed by the sol–gel method, while the cubic form is obtained when the coprecipitation approach is used. This work provides experimental evidence of the formation of both phases by using the same reactants and thermal conditions and only modifying the technical procedure. The formation and stability of each phase are analyzed by temperature-dependent measurements, and the observed crystal structure differences are used to propose a potential fundamental explanation to our observations based on differences in the cations’ distribution and Jahn–Teller distortion. Moreover, different copper ferrite purities and particle sizes are found when using each of the methods. The spherical shape of the particles and their tendency to sinter, forming micrometric clusters, are observed by electron microscopy. Finally, the divergence in magnetization between the samples prepared by each method supports our argument about the different cations’ distribution and opens the door to a wide range of different technological applications for these materials.