Microstructural Evolution of Crystalline‐Oriented (K_0.5Na_0.5)NbO₃ Piezoelectric Ceramics with a Sintering Aid of CuO

Abstract

The microstructural development of crystalline-oriented (K 0.5 Na 0.5 )NbO 3 (KNN)-based piezoelectric ceramics during sintering was investigated. The addition of CuO as a sintering aid was found to be effective for fabricating highly oriented and dense KNN ceramics. KNN specimens containing 0.5-1.0 mol% CuO sintered at 11001C for 1 h were found to have relative densities and pseudo-cubic {100} orientation degrees of 95% or higher. In the early stages of sintering, KNN is formed in the reaction between complementary reactants NaNbO 3 and KNbO 3 , after which oriented grain growth proceeds at a relative density of more than 90%. In addition, the results of transmission electron microscopy observation showed that textured KNN ceramics have a unique pectinate-like domain structure with domain walls consisting of {101} planes. 1951J ournal

Structure and electrical properties of K0.5Na0.5NbO3–LiSbO3 lead-free piezoelectric ceramics

“…Therefore, there is a great need to develop lead-free piezoelectric ceramics with excellent piezoelectric properties for replacing the lead-containing ceramics in various applications. Several lead-free piezoelectric ceramics such as Bi 0.5 Na 0.5 TiO 3 -based materials, [1][2][3][4] Bi-layered structure materials, 5,6 tungsten bronze-type materials, 7 BaTiO 3 -based ceramics, 8 and alkaline niobatebased materials [9][10][11][12][13][14][15][16][17][18][19][20][21] have been extensively investigated. An important progress of grain-oriented alkaline niobate-based ceramics has been reported recently 22 and piezoelectric ceramics should be "lead-free at last."…”

Microstructure development and texture formation in lead-free piezoelectric ceramics prepared by templated grain growth process

“…71) Takao et al examined the microstructure development in a rather simple system, K 0.5 Na 0.5 NbO 3 with a sintering aid CuO. 16) Kikuchihara and Kimura examined the microstructure development in K 0.5 Na 0.5 NbO 3 with and without CuO. 35) Here, the microstructure development in K 0.5 Na 0.5 NbO 3 without CuO is shown in Fig.…”

“…Takao et al reported that the elimination of pores to less than 10 vol % is necessary for the growth of the template grains. 16) This means that the pores hinder the grain boundary migration. When the pore volume decreases to less than 10 vol %, the pinning and drag effects of pores diminish.…”

“…The grain size in the final product is determined by the sintering conditions, i.e., soaking temperature and period. 26) In K 0.5 Na 0.5 NbO 3 , the template grains with 0.5¯m thickness and 1015¯m side length grow to cuboidal grains of size 1020 m. 16) The growth perpendicular to the plate faces can consume a fairly large volume of the matrix grains and a template content of 5 vol % is normally used. 16),22),32),86), 87) When the growth of the template grains is stagnant or slow, the template grains consume a small volume of the matrix grains.…”

“…Thus, dense textured ceramics are obtained. At first, the presence of a liquid phase was thought to be preferable, 15), 16) but later it is found that the liquid phase is not necessarily required. 17), 18) Initially, the application of TGG was limited to materials with crystal structures having low crystallographic symmetry, because it was thought that no techniques are applicable for the preparation of anisometric grains for materials with high symmetry.…”