Lead-free piezoelectric materials with low sintering temperature
Date of Issue2016-12-12
School of Mechanical and Aerospace Engineering
A*STAR Institute of Materials Research and Engineering
This report aims to study strategies of lowering sintering temperature of lead free(KNN) based piezoelectric ceramics and investigate their microstructure, electrical and electromechanical properties. Lowering the sintering temperature has been an issue with KNN ceramics as they do not densify well at low sintering temperatures and this causes their electrical and electromechanical properties to decline. Some processes and methods from prior works done in this field of KNN ceramics have been adopted by the author in this experiments. There were two experiments, Experiment A and B, conducted using two lead free KNN based piezoelectric ceramic, (KNN-BZN) and (KNN-5LT).The sintering temperature was lowered by controlling the concentration of alkali ions. Firstly in Experiment A, lead free (KNN-BZN) based ceramic samples were fabricated by conventional ceramic processing and sintering. Excess lithium carbonate and excess sodium carbonate were introduced as sintering aids to lower sintering temperature of the ceramics. These sintering aids were chosen based on their low melting point so that they can promote a slight liquid phase during low temperature sintering to promote better electrical and electromechanical properties while lowering the sintering temperature. This liquid phase diffuses into the KNN perovskite structure after the completion of sintering, forming single phase perovskite structures thereby improving properties. Potassium carbonate and sodium carbonate were also added in excess to control volatilization of alkali ions during high temperature calcination and sintering process. The properties such as density, dielectric property, ferroelectric property, piezoelectric property, microstructure and phase boundary of ceramic pellets were measured to see the effects of lowering the sintering temperature on the properties. The highest d33 obtained were 280.42 pC/N and 270.92 pC/N for samples sintered at 1200°C for 4 hours with no addition of sintering aids which include sodium carbonate and lithium carbonate. This samples also had a good relative density of 95.08% and 93.2%. Secondly in Experiment B, lead free (KNN-5LT) based ceramic samples were fabricated using conventional ceramic processing and sintering. Effect of addition of excess lithium carbonate as sintering aid on lowering the sintering temperature was studied. Lithium carbonate was chosen based on its low melting point so that it can promote a slight liquid phase during low temperature sintering to promote better electrical and electromechanical properties while lowering the sintering temperature. Then properties such as density, dielectric property, ferroelectric property, piezoelectric property, microstructure and phase boundary were studied to see the effects of lowering sintering temperature. The highest d33 achieved in this experiment was the sample which was sintered at 1100°C for 4 hours and with 1 mol% of excess lithium. The highest d33 achieved was 124.62 pC/N and the relative density was close to 88.3%.
Final Year Project (FYP)
Nanyang Technological University