Preparation And Size Effect Of Niobate-based Lead-free Piezoelectric Material

Piezoelectric materials have wide application in our life,but the traditional PZT piezoelectric ceramics with high lead content is hard to meet the requirements of the ceramic material.With the development of social economy,more and more attention to people’s life environment,lead-free piezoelectric materials has become a focus in the study of piezoelectric ceramic materials.By the good piezoelectric performance,iron electric performance and the advantage of high Curie temperature,KNN ceramics has become one of the hot research materials.In this paper,from the perspective of environment protection,KNN powders were prepared by hydrothermal method,sol-gel method and molten salt method.Meanwhile,KNN ceramics was prepared by two step sintering,respectively.The phase structures,surface morphologies and size effect were studied in detail.The main research contents are as follow:1、The KNN powders with perovskite structure synthesized by hydrothermal method at 200 ℃,6 h.The reaction time,initial potassium sodium ratio and total alkali concentration determine the structure and morphology of the final KNN powders.The crystals have growth with the response time,while it will not affect the growth of crystals with longer reaction time.KNN powders with the two phase coexistence were prepared while initial potassium sodium ratio changed.The Rich microstructure of sodium KNN microstructure was nanorods while rich potassium of KNN was cube.With the increase of total alkali concentration,crystal of KNN changed from tetragonal phase to orthorhombic,and crystal crystallinity increased,gradually.2 、 Hydrogen niobium oxide was prepared using new method.The crystallization temperature,reaction time and heating rate determine the structure and morphology of KNN powders.Sol gel method significantly reduces the crystallization temperature of KNN powders.With increase of crystallization temperature,the KNN crystal is two phase coexistence,and the crystal growth was promoted.The extension of reaction time is also promoted the crystal growth.Crystal has the best heating rate,namely 4℃/min,which lead to the best crystals crystallinity.3、The experimental parameters in molten salt method influence on KNN powders were studied emphatically.The types and characteristics of initial powders in the molten salt method is the basis of the KNN powders crystal microstructure changed.On this basis,the molten salt content,the type of molten salt and crystallization temperature can change the crystal structure and microstructure of KNN powder,especially a wide range of size distribution of KNN powders was obtained as the crystallization temperature changed.Molten salt determines crystal temperature of KNN,at the same time it controls the crystal microstructure of KNN powders.With increasing of the molten salt content,the crystal crystallinity increased,which had nothing to do with the microstructure.4、KNN ceramics powder was obtained by two-step sintering process with distribution grain size.The smaller the initial powder grain size,the higher the density and the dielectric constant of the KNN ceramic samples,at the same time,the crystal phase of initial powder also determine the stability of ceramic performance.Sintering can driving force mainly comes from the crystal interface.The smaller the grain size,the higher the crystal interface can,so as to promote the sintering process,which makes the KNN ceramics block with high density and dielectric constant.The powders with two phase coexistence had stability density and performance of the ceramics with low temperature sensitivity.