Abstract: In this work we study the behaviour of the dielectric constant of BaTiO₃ single crystals doped with Cu and Fe for different ion percentages, particularly, the influence of these heterovalent substitutions on the ferroelectric-paraelectric phase transition whose temperature is found at T_c=120 °C for pure samples. The dielectric constant ε in terms of temperature shows that the Curie temperature decreases when the quantity of impurities increases and presents a broadening and flattering of the maximum of ε(T) within higher values, with the transition becoming more and more diffuse. It is interesting to have a material with very high permittivity (high-k) because of its capacity to store an important quantity of electric charges. The ε anisotropy and the Curie-Weiss law are also verified with a good ratio between the slopes of ε⁻¹(T) from both sides of the transition, leading to a Curie constant: C=13×10⁴ K for BaTiO₃:1.6%Fe in the polar phase. BaTiO₃ is a displacive ferroelectric going through a first-order phase transition. The substitutions have an effect on the dynamics of the perovskite lattice. They induce charges transfer to Ti and a diminution of elastic forces in BaTiO₃. Then we discuss the fact that the maximum of permittivity does not depend on the phase transition but on the nature of the material.

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