X7R type lead complex perovskite ferroelectric ceramics with high dielectric constant
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X7R type lead complex perovskite ferroelectric ceramics with high dielectric constant Lijian Ruan, Longtu Li, and Zhilun Gui Department of Materials Science and Engineering, Tsinghua University, Beijing 100084, The People’s Republic of China (Received 17 December 1996; accepted 5 May 1997)
A new X7R type dielectric ceramics for the PMN-BT-PT system with a high dielectric constant (4832) and a low firing temperature (1100–1130 ±C) was prepared by the mixed-sintering method. The results of XRD, SEM, EDAX, and dielectric measurements showed that the dielectric ceramics is a two-phase composite with the high dielectric constant originating from the ferroelectric relaxor, and the temperature stability of the dielectric properties from two-phase coexistence.
X7R type dielectric materials for multilayer ceramic capacitors (MLC’s) are a type of temperature-stable dielectrics that requires the capacitance values in the temperature range from 255 ±C to 125 ±C to be within 615% of the capacitance at 25 ±C. They have been extensively used in many areas including electronic equipment for data processing, military and automotive applications, and telecommunications. As known, conventional X7R dielectrics are mainly based on two kind of modified barium titanate, that is, high firing temperature and low firing temperature barium titanate based dielectrics.1,2 A higher dielectric constant of 4200 can be obtained within a higher firing temperature of 1350 ±C, resulting in the use of relatively expensive inner electrodes. Therefore, complex lead perovskite ceramics have attracted much attention in the last decade because of their potential use as MLC’s. Lead magnesium niobate Pb(Mg1/3 Nb2/3 )O3 (PMN), with high dielectric constant, broad maxima, and relatively low firing temperature, is a promising material for multilayer ceramic capacitors.3–5 The temperature stable high dielectric (1 2 x)PMN 2 xPT system has already been reported.6 The temperature characteristic did not, however, meet X7R specifications. A new PMN-PMW-PT system relaxor exhibiting more temperature-stable dielectric properties was developed, but only satisfying the X7T specifications.7 A material meeting the JIS YB specification and having high dielectric constant has been developed in PMN-PT-PMW ternary system.8 Recently X7R type lead-based complex perovskite dielectrics of PMW-PT-PNN and PMW-PZ-PT systems with dielectric constant 3000–3700 were also investigated.9,10 But so far no dielectric ceramics with higher dielectric constant (more than 4500) and lower firing temperature (less than 1150 ±C) have been reported. In this work, a new material meeting the X7R specification and having high dielectric constant (4832) has been developed from a J. Mater. Res., Vol. 13, No. 2, Feb 1998
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composition based on two kinds of lead perovskite relaxors using a mixed sintering technique at lower firing temperature (1100–1130 ±C). In this communication, the dielectric propertie
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