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Influence of Sintering Temperature on Grain Growth and Phase Structure of Compositionally Optimized High‐Performance Li/Ta‐Modified (Na,K)NbO 3 Ceramics

2009; Wiley; Volume: 92; Issue: 8 Linguagem: Inglês

10.1111/j.1551-2916.2009.03128.x

1551-2916

Zong‐Yang Shen, Yuhua Zhen, Ke Wang, Jing‐Feng Li,

Microwave Dielectric Ceramics Synthesis

Microstructure characteristics, phase transition, and electrical properties of (Na 0.535 K 0.485 ) 0.926 Li 0.074 (Nb 0.942 Ta 0.058 )O 3 (NKN‐LT) lead‐free piezoelectric ceramics prepared by normal sintering are investigated with an emphasis on the influence of sintering temperature. Some abnormal coarse grains of 20–30 μm in diameter are formed in a matrix consisting of about 2 μm fine grains when the sintering temperature was relatively low (980°C). However, only normally grown grains were observed when the sintering temperature was increased to 1020°C. On the other hand, orthorhombic and tetragonal phases coexisted in the ceramics sintered at 980°–1000°C, whereas the tetragonal phase becomes dominant when sintered above 1020°C. For the ceramics sintered at 1000°C, the piezoelectric constant d 33 is enhanced to 276 pC/N, which is a high value for the Li‐ and Ta‐modified (Na,K)NbO 3 ceramics system. The other piezoelectric and ferroelectric properties are as follows: planar electromechanical coupling factor k p =46.2%, thickness electromechanical coupling factor k t =36%, mechanical quality factor Q m =18, remnant polarization P r =21.1 μC/cm 2 , and coercive field E c =1.85 kV/mm.