Effects Of Raw Materials And Acceptor Doping On Preparation And Electrical Properties Of KNN-based Lead-free Piezoelectric Ceramics

(K,Na)NbO₃ lead-free piezoelectric ceramic materials are considered as the most potentially candidate for PZT lead-based ceramics.In recent years,KNN-based ceramics have attracted a great deal of attention.This paper focused on the influence of niobium oxide raw materials and acceptor doping on the sintering and electrical properties of KNN-based piezoelectric ceramics.The two-step sintering method is used to improve the performance of KNN and how to prepare KNN-based high entropy ceramics oxide is discussed.Firstly,KNN ceramics prepared from four kinds of different niobium oxide as raw materials were analyzed.The KNN ceramics prepared from four niobium oxide are obviously different in micro-structure and electrical properties.Under the existing experimental conditions,the d33 of KNN ceramics which used high purity niobium oxide as raw material can reach 129Cp/N,which is obviously superior to the KNN ceramics prepared from other niobium oxide as raw materiasl.The two-step sintering method can effectively eliminate the negative impact of KNN ceramics used the monoclinic niobium oxide as the raw materials and the d33 is effectively improved which similar to the d33 values that reported in the literature.The influence of Cu²⁺,Sc³⁺,Ge⁴⁺ acceptor doping on the sintering and piezoelectric ferroelectricity of KNN-based ceramics was also studied.Suitable Cu²⁺doping could significantly increase the Qm of KNN ceramics,while the doping of Sc⁵⁺and Ge⁴⁺have no obvious effect on the improvement of Qm.Different elements have different effective charges,which have different interaction force with the oxygen vacancies.When Cu²⁺replace the Nb⁵⁺result in defects and this defects will react with oxygen vacancy defects to form a defect dipole,which can limit the movement of the domain walls,thereby increasing the mechanical quality factor.In order to investigate how to prepare high-entropy ceramics by introducing elements such as Li⁺,Ag⁺,Ba²⁺,Mg²⁺,Bi³⁺,Ti⁴⁺,Zr⁴⁺,Sb⁵⁺and Ta⁵⁺ into KNN ceramics,the experimental results show that in the formula（1-x）（K0.48Na0.52）0.95Li0.05]（Nb0.85Ta0.15）O3-xBi（Mg0.5Ti0.5）O3)abbreviation（1-x）KNN-xBMT（x = 0,2,4,6,8,10,12,14,16mol%）can get high entropy oxide ceramics,the increase of entropy will lead to the transformation of the（1-x）KNN-xBMT from tetragonal phase to cubic phase.