Preparation Of The Rare-earth Doped Textured CaBi₄Ti₄O₁₅（CBT） Ceramics

As a typical bismuth layer-structure ferroelectrics, CaBi₄Ti₄O₁₅ceramics has a highcurie temperature, low dielectric constant and other properties in the field of hightemperature, the transducer has considerable prospects and value. However, theparticularity of the self bismuth layer-structure greatly limits its polarization, whichgreatly affecting the important electrical performance and piezoelectric activity ofceramic materials.Fortunately, as the large differences in three-dimensional axial growth rate, thegrains are easy to grow into plate-like powders which morphology can easily to begrain-oriented operation by some special process to make the dominant crystal facearrangement in the same direction. Thus, reinforcing the dominant crystal face avariety of electrical performance and getting the most out of the spontaneouspolarization to improve the using value in a characteristic direction of the CBTceramics.The Molten Salt Synthesis （MSS） method is used in this paper to accelerated, andpromoted the diffusion and crystal growth of the raw material powders in a liquidenvironment. The powders with great morphology which applied to tape-castingprocess needs of the textured ceramic were obtained through the MSS. Powders inorganic solvent were arranged in the same plane by Oriented Consolidation ofAnisometric Particles （OCAP） technology. After cooling, shaping and sintering,textured CaBi₄Ti₄O₁₅ceramics were obtained.It is found that the length of MSS holding time shows a obvious control effect onthe powders morphology in the for powders preparation process. While in theorientation and tape-casting operations,37wt%organic carrier of the flow castingslurry has the best casting nature. The movement behavior of plate-like powderparticles in tape-casting operation and the reason of particles arranging orientationwere discussed. After sintering, the measurement results of textured ceramics in different directions testified its anisotropic electrical performance, and theperformance on plane which perpendicular to the direction of orientation is far betterthan the direction of the parallel side. Simple texture modification can get more thantwice electrical performance increasing. On this basis, the rare earth ion-doped Bi-bittextured ceramics further enhancing the advantages of the dominant planeperformance, the biggest value up to3times more.In the analysis of the effect of selected doping ions and their molar concentration toceramic electrical properties, it was found that the doping ions which replacing Bi bitshow a distinct relationship with their radius size. Because the changing of ions radiusbroke the tolerance factor in bismuth layer-structure. A smaller ion replacing makesthe system structure unbalance.In the analysis of the degree of orientation of the textured ceramic, it was found thatsintering temperature show the leading role in the orientation effect. Doping type anddoping concentration show less impact on the orientation. Rare-earth doped texturedCaBi4Ti4O15ceramics obtained in this research owned the maximum dielectricconstant up to400, the maximum piezoelectric coefficient up32pC/N, the maximumremnant polarization about5.2μC/cm², the maximum value degree of orientation94%and the maximum relative density up to87%.