Preparation, Structure And Properties Of Strontium Barium Niobate/Barium Strontium Titanate Multi-phased Ceramics

In this thesis, (1-x)BaO·xSrO·(1-y)TiO₂·yNb₂O₅ (SBN/SBT) with coexistence of Strontium barium niobate(Sr_xBa_1-xNb₂O₆,0.25≤x≤0.75, SBN) and barium strontium titanate (Sr_xBa_1-xTiO₃, SBT) were successfully prepared by a powder-sol method, and the formation mechanism of the composite ceramics was investigated in details. By X-ray diffraction (XRD), Scanning electron microscope (SEM), X-Ray Photoelectron Spectroscopy (XPS), LCR digital bridge and electrometer, the phase structure, dielectric properties and the pyroelectric properties of SBN/SBT composite ceramics were also studied. Following results can be obtained from this thesis:SBN/SBT composite ceramics have been prepared by powder-sol process. The powder-sol process parameters were: 800℃for presintering temperature, 1250℃for sintering temperature, 3h for sintering time. SBN/SBT composite ceramics with uniform SBT and SBN grains size and high density were obtained by powder-sol process parameters. The formation mechanism is put forward for the SBN/SBT composite ceramics by powder-sol process. The influence of Nb/Ti ratios, Sr/Ba ratios, La³⁺ doping on relative density, grain morphology and dielectric loss were studied.The new formulasΔ(O-Nb) = BE[O_1s(III)]-BE[Nb_3d5/2] andΔ(O-Ti) = BE[O_1s(IV)]-BE[Ti_2p3/2] are put forward. By the above formula, the influences ofΔ(O-Nb) andΔ(O-Ti) on dielectric loss was studied. The relationship betweenΔ(O-Nb),Δ(O-Ti) and dielectric loss was explained. ByΔ(O-Ba) = BE[O_1s(I)] - BE[Ba3d5/2] andΔ(O-Sr) = BE[O_1s(II)]-BE[Sr_2p3/2] being put forward, the influences ofΔ(O-Ba) andΔ(O-Sr) on dielectric constants was explained. With Nb/Ti ratios nearing 5:5, the reversion force of lattice vibration for O-Nb and O-Ti bond are increased gradually. This decreases tanδfor composite ceramics. It helps to increase the FOM (figure of merit, FD) of composite ceramics. TheΔ(O-Ba) andΔ(O-Sr) for O-Ba and O-Sr bond are increased gradually. This help to increase dielectric constants for SBN/SBT composite ceramics. The pyroelectric coefficient have more wide pyroelectric coefficient reponse than those of (Ba_0.7Sr_0.3)TiO₃ and (Ba_0.7Sr_0.3)Nb₂O₆ for SBN/SBT composite ceramics.The influence of La₂O₃ doping on structure and properties for the 0.7BaO·0.3SrO·0.5TiO₂·0.5Nb₂O₅ composite ceramics was studied. The relative density and dielectric loss were improved by La₂O₃ doping. This helps to improve the FOM for composite ceramics. The XPS for the (0.7-z)BaO·(0.3-z)SrO·zLa₂O₃·0.5TiO₂·0.5Nb₂O₅ were studied. It is shown that the binding energy of Nb3d5/2 was not influenced by La₂O₃ doping. The binding energies of Ti2p were strongly dependent on La₂O₃ doping. The influences of La₂O₃ doping on the O-Nb and O-Ti bond are put forward to byΔ(O-Nb)= BE(O_1s)-BE(Nb_3d5/2) andΔ(O-Ti) = BE(O_1s)-BE(Ti_2p3/2). The SBN/SBT with La³⁺ doping has higher FOM than those of (Ba_0.7Sr_0.3)TiO₃ 0.7BaO·0.3SrO·0.5TiO₂·0.5Nb₂O₅ and (Ba_0.7Sr_0.3)Nb₂O₆.