Na2co3 and Er2o3 Modified Lead Free Knn Piezoelectric Ceramic Obtained by Hot Pressing

Abstract

Analysis of dense KNN ceramic obtained by hot pressing (HP) methodat 1100°C are presented in this paper. The synthesis of KNN-based piezoelectrics meets following challenges: low density of material, uncontrolled K/Na ratio, multiphase composition and formation of different KNN structures. Classical hot pressing approach results incontaminationby carbon originating from graphite moulds. The proposed h-BN protection layer between green sample and graphite mouldprevented carbon reaction with powder. Additionally, h-BN presence may decrease formation of oxygen vacancies which allows to maintain semiconductor features of KNN structure. Remaining issues were addressed with the addition of excess Na and Er2O3 doping. The results showed that excessNa addition allowed to compensate evaporation of sodium during the synthesis and sintering. Er2O3 was added as sintering aid to limit abnormal grain growth. The modification of amount of Na and Er2O3 addition resulted in high purity KNN samples with tetragonal structure andapparent density higher than 97%. Finally, piezoelectric features of prepared dense samples were measured and presented.