**6. Conclusion**

In this chapter, synthesis methods of cobalt phosphates and metallo-cobalt phosphates in the crystalline form have been described: single crystals and/or polycrystalline powders. The structural studies of the studied compounds show structural diversity with open anionic frameworks showing tunnels (3D) and inter-sheet space (2D). However, it shows that the electrical property is related to the structural characteristics of the material. In order to correlate structure and physical properties especially electrical properties of metallo-cobalt phosphates, structural factors influencing the ionic conductivity have been treated. Based on the structural characteristics, the electrical properties of the crystalline materials can be modeled theoretically, especially in the case of purely ionic conductors. In fact, it is possible to determine the value of the activation energy which corresponds to the minimum energy that must be supplied to an ion to move from one site to another site in the

### *Cobalt Compounds and Applications*

crystal lattice. In addition, these modelizations are based on the structural data of the crystal. Since the measurements are often performed on ceramics, it is also necessary to take into account the effect of the relative density of the ceramic: effect of the microstructure.
