Study On Low Temperature Dielectric Relaxation Behavior Of Bi_1.5ZnNb_1.5O₇Ceramics

Bi₂O₃-ZnO-Nb₂O₅（BZN） pyrochlore ceramics has been considered one of the promisingcandidate dielectric materials because of the four essential properties:（1） reasonable dielectricconstant,（2） low dielectric loss,（3） controllable temperature coefficient of capacitance,（4） lowsintering temperature. Simultaneously the higher dielectric loss occurs at microwavefrequencies. It was considered that the dielectric relaxation could contribute to the dielectricloss of BZN based dielectrics in microwave devices at room temperature. So far, the physicalnature of the low temperature dielectric relaxation for BZN ceramics is not completely clear.In this paper, Ca²⁺, Yb³⁺, Ho³⁺and Ce⁴⁺substituting for A-site or B-site were doped inα-BZN ceramics respectively. The microstructure, the relationship between the microstructureand the dielectric relaxation, and the physical mechanism of the dielectric relaxation wereinvestigated, the main results are as follow:1. The experiment confirmed that there is a lower solid solubility in Nb⁵⁺site than Bi³⁺site,which is in accordance with the modeling result by GULP, the lower solid solubility in B-site ofpyrochlore ceramics is attributed to the smaller ionic radius of Nb⁵⁺. With the doping contentincreasing, for A-site or B-site doped α-BZN ceramics, the lattice constant a decreases, thebond valence sum （AVs） increases, the dielectric constant declines, the dielectric loss increases.In Bi_1.5ZnNb_1.5O₇ceramics, with the increase in doping content, the x values of48f O-siteincrease, a decrease in relaxation degree occurs.2. In microwave dielectric ceramics, apart from the polarizabilities of ions, the dielectricconstant also is affected by the AVs, In Bi_1.5ZnNb_1.5O₇ceramics, with increasing the dopingcontent, the dielectric constant is inversely proportional to the AVs of A₄O, the dielectric loss isclosely related to the extrinsic loss.3. The relaxation degree is inversely proportional to x value, the increasing x value impliesthat the cubes become more regular, so it is believed that the dielectric relaxation for theceramics with pyrochlore structure is closely related to the change from prefect octahedral toregular cube, the closer the prefect octahedral, the greater the relaxation degree, the closer theregular cube, the smaller the relaxation degree.4. The interaction between the two networks, representing2-3%of the total electrostaticenergy of the system, strengthen with increasing the value of x, which could be associated withthe declining relaxor behavior.5. The A-O′bond valence increases, so the bond energy of the A-O′bond strengthens,which retard the relaxor behavior.