Study On The Regulation Of The Density And Properties Of BaTiO₃-based Ceramics For Laminated PTCR

In recent years, with the rapid development of microelectronics and the surface mounttechnique （SMT）, BaTiO₃–based PTCR （positive temperature coefficient resistance）devices also are moving in the direction of miniaturization, low resistance and laminated.Currently, BaTiO₃–based PTCR were fabricated via tape casting technique andreduction/reoxidation process. The appropriate density is very important for the PTCRdevices during the fabrication process. This thesis mainly focuses on the study of theregulation of the density of BaTiO₃–based ceramics and the molding technology for thepreparation of high performance multilayer PTCR components.There are a lot of factors that affect the density of the BaTiO₃ceramics. Firstly, thispaper investigate the influence of the amount of the binder on the BaTiO₃ceramics preparedby tape casting technique in the condition of other fabrication factors are optimized. In thecondition of good mechanical properties of green body, we can regulate the green density ofthe PTCR devices in the range of50-60%, and the sintered density of the PTCR devices inthe range of60-90%. The grain size of samples from different binder amount was scarcelychanged with different binder amount since the reduction-sintering temperature was thesame. The withstanding voltage value and the PTCR jump of BaTiO₃ceramicsmonotonically decreased as the binder amount increased, while the room temperatureresistivity had a different trend versus binder amount. We also studied the influence ofsintered process on the BaTiO₃ceramics within the same binder amount. We found that thesample with8.4wt%binder amount was good for tape casting and showed a roomtemperature resistivity of56·cm and PTCR jump of3.2orders of magnitude whenreduction-sintered at1150°C and reoxidized at800°C. In addition, we also explored thewater-based casting process. The green mechanical properties of the water-based castingsamples were worse than the solvent-based casting samples. And the range of the density ofwater-based casting BaTiO₃ceramics was narrow. We still successfully determined a more mature water-based casting formulation, the green density of the water-based castingsamples was40%, and the relative density of the BaTiO₃ceramics sintered in1150°C was78%. The water-based casting BaTiO₃ceramics showed a resistivity of14.6cm, a PTCRjump about3.6orders of magnitude and the Curie temperature is85.7°C.By changing the content of SiO₂in the BaTiO₃ceramics, we found that the sintereddensity of the samples was monotonically reduced as the SiO₂amount increased, and thePTCR jump gradually decreased with the increasing SiO₂amount, while the roomtemperature resistivity had a different trend versus SiO₂amount. The Curie temperature ofBaTiO₃ceramic samples was gradually moved to high temperature with the SiO₂amountincreased.