Study On Preparation And Size Effect Of Fine Grain High Temperature BiScO₃-PbTiO₃ Ceramic

Nanopowder of (1-x)BiScO3-xPbTiO3 (BSPT) ceramic was successfully synthesized using citric acid chemical mehod. Subsequently, the techniques of preparing high-performance fine-grain ceramics via two-step sintering method were investigated and optimum parameters obtained. Kinetic window for reaching full density without grain growth was defined. Experimental evidences show the Morphotropic phase boundary (MPB) location around x=0.635 for BSPT ceramics. Consequently, BSPT ceramics with a piezoelectric coefficient as high as 700pC/N, as well as an average grain size of 1.47μm were successfully prepared, and their ferroelectric properties were investigated. Finally, the grain size effects on ferroelectric properties including piezoelectric properties and Curie temperature were studied as well. Besides, the technique of preparing BSPT ceramics through Spark Plasma Sintering (SPS) was also investigated.The average grain size of nanopowders prepared by citric chemical method was around 10nm, as measured by both the peak broadening of X-ray diffraction and Transmission Electron Microscope (TEM). Experiments reveal that T1=1000℃, T2=800℃is an optimum combination to ensure a high density as well as the finest grain grain size.Experimental evidence indicates the existence of MPB at the composition x=0.635, which exhibits a piezoelectric coefficient d33 of 700pC/N and an electromechanical coupling factor kp of 0.632 at room temperature, significantly higher than the reported values to date. The local effective piezoelectric coefficient d33* was estimated to be 795pC/N at 2.29V, measured by scanning probe microscopy. Further observation revealed the existence of 90°domains of about 60~70 nm in width, confirming the previous results that small domain structure enhances the piezoelectric properties.Consequently, the grain size effects on piezoelectric properties & Curie temperature were studied as well. The d33 increases with decreasing average grain size when the grain size is below 800nm, while it shows a peak in 1.47μm when above 800nm. The Curie temperature versus grain size does not show a clear trend, however, a relatively high value was observed around 600nm, which was explained by the existence of multi-domain structure confirmed by subsequent TEM observation.