Study On Dielectric Properties Of Bi-based Pyrochlore Ceramics

In this paper, Bi-based pyrochlore ceramics were prepared by a solid phase reactionmethod. The effect of A-site and B-site substitution with different ions on structurecharacteristic and dielectric properties of ceramics was investigated and the factors whichcause the dielectric relaxation behavior of ceramics were discussed.1.The effect of Dy3+and Ta5+substitution on the dielectric properties and structurecharacteristics was investigated. When x≤0.15mol, The crystal structure of BDZN ceramicsis the cubic pyrochlore structure (α-BZN). But for BTZN ceramics, the second phase occurredwhen x=0.05, which may be due to the low structure tolerance for high charge ion inpyrochlore. The bond valance calculations show that the AV(O’) of BDZN ceramics increasewith Dy3+increasing, while the AV(O’) of BTZN ceramics decrease with the increase of Ta5+content. Typical dielectric relaxation can be observed at low temperature for BDZN andBTZN ceramics. The Tmshifts toward lower temperature direction with the amount ofsubstitution increasing. The Arrhenius fitting calculation show that Eain low temperaturedecreases with the amount of substitution increasing. The degree of dielectric relaxation isclosely related to the disorder in A-site. The more structure disorder, the stronger the structurerelaxation. The degree of dielectric relaxation increase with the structure disorder increasing.2. The effect of La3+，Ru4+，V5+，Ta5+，W6+and Mo6+substitution on the dielectricproperties and structure characteristics was investigated. The crystal structure of BZNNceramics is the cubic pyrochlore structure (α-BZN). The ζ of48f(O) increase with thesubstitution increasing. The Arrhenius fitting calculation show that Eain low temperature isclosely related to the shift of peak temperature. With La3+and W6+increasing, Eadecreasesand Tmshifts towards lower temperature direction. For Ru4+，V5+，Ta5+, and Mo6+, Eaincreases with the amount of substitution increasing and Tmshifts towards higher temperaturedirection. The degree of dielectric relaxation(△Tf) is associated with the change ofbond-valance sum, bond energy of RA-O’and the disorder in crystal.3. The effect of Sc3+and Ru4+co-substitution on the dielectric properties and structurecharacteristics was investigated. With Ru4+increasing, the averge bond length of RA-Odecreaseand RB-Oincrease. The bond valance calculation show the AV(O’)[A4] of BSZNR ceramicsincrease and AV(O)[A2B2] decrease with the amount of Ru4+increasing. The calculations ofArrhenius and Curie-Weiss fitting have the same characteristic. Ea increases and the peaktemperature of BSZNR ceramics shifts toward higher temperature direction with Ru4+increasing, while γ and△Tfof BSZNR ceramics decrease.