Study Of Doping And Dielectric Properties In Lead-Free BaTiO₃-based Ceramics

The effects of Sm₂O₃, Y₂O₃ and NiO on microstructure and dielectric properties in BaTiO₃-based ceramics are investigated, respectively. Based on the effects of Sm³⁺, Y³⁺, and Ni²⁺ on the microstructure and dielectric properties, the substitution mechanism of Sm³⁺, Y³⁺, and Ni²⁺ in BaTiO₃-based ceramics is also investigated and discussed, respectively. The research achievements are as follows:There is an alternation of substitution preference of Sm³⁺ and Y³⁺ for the host cations in perovskite lattice, that is, Sm³⁺ and Y³⁺ enter the A site in perovskite lattice at first, then they enter the B site when the additive amount of Sm³⁺ and Y³⁺ exceed some value. Owing to the substitution preference, the crystal cell a and dielectric constant rise at first, if the amount continues increasing, they will decrease. Both Sm³⁺ and Y³⁺ can improve the dissipation factor, especially, the optimized dissipation factor is 0.0015 for 1.0 mol%-Y³⁺-doped samples, making it a superior candidate material for applications. There is an obvious distinction for the effects on dielectric properties between Sm³⁺ and Y³⁺, that is, the Y³⁺, not Sm³⁺, makes the BST ceramics exhibit the diffuse phase transition.It is also found that Ni²⁺ can enter the B site in ABO₃ perovskite at first, making the crystal cell a rise, whereafter, Ni²⁺ ions most segregate on the grain boundaries to inhabit the grain growth, forming the BST/NiO composites. Due to the decrease of grain size and the impurity, the dielectric constants are decreased. It is concluded that the diffuse phase transition is linked to the adulteration of Ni²⁺, and the diffuse phase transition increases with the doping level increasing, leading to that the peaks of dielectric constants become slower and flatter.The results indicate that the crystal structures are perovskite phase for all of the examined samples in BTS10 and BZT20 ceramics, however, contrasting to the blank sample, the grain size of the sample with Sm₂O₃ addition is decreased. Owing to the substitution of Sm³⁺, the dielectric constant rises at first, if the amount continues increasing, it will decrease, in the mean time, the dissipation factor also comes to its maximum when the dielectric constant is the highest. The relation between Tm and the concentration of Sm₂O₃ has some similarity except that Tm does not move in BTS10 ceramics at first, resulting from a handful of Sm³⁺ entering into the B site. All of the samples exhibit the diffuse phase transition with Sm₂O₃ addition, however, there are two obvious distinction among BTS10 and BZT20 ceramics. First, the blank sample of BTS10 has no diffuse phase transition in nature, the samples of BTS10 can exhibit diffuse phase transition only when the Sm³⁺ ions are added, on the contrary, the blank sample of BZT20 possesses the diffuse phase transition in nature. Second, the diffuse phase transition congruously increases with the level of the Sm³⁺ doping increasing in BTS10 ceramics, however, the diffuse phase transition lowers in the beginning in BZT20 ceramics, if the amount continues increasing, it will increase, which demonstrated that a handful of Sm³⁺ ions have entered into the B site in BTS10 ceramics but not in BZT20 ceramics in the beginning, proved by the distinction of the relation between Tm and the concentration of Sm₂O₃ at first.