**3. Morphology of ZnCu ferrites**

The spinel structure [61]. of ZnCu ferrite consists one major unit cell composed of 8 sub-unit cells having face-centered cubic (FCC) structure with two types of sites in each unit cell i.e. tetrahedral (A) site and octahedral (B) site. There are 64 tetrahedral interstitial sites and 32 octahedral interstitial sites. Spinel structure has closed packed oxygen atoms arrangement in which 32 oxygen atoms form a unit cell. Tetrahedral (A) sites are surrounded by four nearest oxygen atoms and octahedral (B) sites have six neighboring oxygen atoms. In ZnCu spinel ferrite lattice, Zn ions are on the tetrahedral sites while Fe and Cu ions occupy both tetrahedral and octahedral sites. Due to this spinel structure, different metallic ions can be added which brings out a change in the electric and magnetic properties of ferrites. The metal ions introduced may enter the spinel crystal lattice by replacingFe3+ ions and leading to aggregation of these ions on the grain boundary. These morphological features of ZnCu ferrite nanoparticles can be tuned to a larger extent to fulfill the application and to select the appropriate synthesis and characterization techniques. To learn the merits of ZnCu ferrites for various applications, the knowledge of different synthesis and characterization techniques is a must.

#### **3.1 Synthesis methods to prepare ZnCu ferrites**

There are two approaches to synthesize nanoparticles: top-down and bottom-up. In top-down, the bulk materials are broken down to get nanosized particles. This

#### *The Presented Study of Zn-Cu Ferrites for Their Application in "Photocatalytic Activities" DOI: http://dx.doi.org/10.5772/intechopen.99535*

method has many shortcomings which include the presence of impurities, crystal defects, usage of metal oxides, the requirement of high temperature, products are inhomogeneous, broad size distribution, and flaws in surface structure. In the bottom-up approach, small atomic building blocks fuse to produce nanoparticles. This is the most conducive method for synthesis as the products are homogeneous, highly pure, and reveals narrow size distribution.

Various synthesis techniques are used to prepare ZnCu ferrite nanoparticles such as the sol–gel method [62], spray pyrolysis process [63], co-precipitation method [64], citrate precursor method [65]. By doping other elements or oxides the structural, electrical, and magnetic properties of ZnCu ferrite can be improved, leading to an increase in saturation magnetization and a decrease in coercivity in the soft ferrites.
