MNb2O6-NaNbO3-SiO2(M=Pb,Ba,Sr)体系玻璃陶瓷纳米复合材料的结构和介电性能研究

应用铸造快冷及可控结晶技术制备3种玻璃陶瓷纳米复合介电材料——PbNb2O6 +NaNbO3 +SiO2 (PNS),BaNb2O6+ NaNbO3+ SiO2 (BNS)和SrNb2O6+ NaNbO3+ SiO2( SNS).研究了这3种复合材料的结晶性能,微观形貌和介电性能.X射线衍射(XRD)的分析结果显示:PNS及SNS的玻璃在750℃可控结晶时,均形成中间相A2Nb2O-7(A=Pb,Sr),且该中间相在850℃时消失,此时形成MNb2O6+NaNbO3(M=Pb,Sr)的高介电常数相,而BNS则未经过中间相,在750℃直接析出MNb2O6+NaNbO3(M=Ba)的高介电常数相.在所有的样品中,随着退火温度的升高,晶粒均有逐渐长大聚集的趋势.同时,SNS玻璃陶瓷在750℃及850℃结晶退火处理时,均析出枝状晶粒,异于PNS和BNS的球状晶粒.由可控结晶技术制备的玻璃陶瓷介电性能受热处理过程中所形成的介电相组成及其体积分数和晶粒尺寸的影响很大.分析测试了这3种体系玻璃陶瓷的介电常数与结晶化处理温度之间的关系及介电常数的电场稳定性.在900℃结晶退火时,PNS玻璃陶瓷具有最高的介电常数( ～501,1 kHz),而BNS的介电常数在0～15 kV ·mm-1的测试范围内具有最好的电场稳定性(＜15％).

Structure and Dielectric Properties of Glass-Ceramic Nanocomposites of MNb2O6-NaNbO3-SiO2( M =Pb, Ba, Sr)

The crystallization,microstructure and dielectric behaviors of glass-ceramic nanocomposites,PbNb2O6 +NaNbO3 +SiO2(PNS),BaNb2O6 +NaNbO3 +SiO2(BNS) and SrNb2O6 +NaNbO3 +SiO2(SNS),were investigated with samples prepared via cast-quenching followed by controlled crystallization.X-ray diffraction studies of glass-ceramics revealed that,in crystallization process,for PNS and SNS,the intermediate phase,A2Nb2O7(A=Pb,Sr),precipitated at about 750 ℃ and disappeared at 850 ℃,and high-er phases,MNb2O6(M=Pb,Sr) and NaNbO3,were formed at this higher temperature of 850 ℃.However,this chemical formula intermediate phase was not detected in BNS,while high-er MNb2O6(M=Pb,Sr) and NaNbO3 crystallized directly at 750 ℃.TEM bright field observation showed that the crystalline particles in all glass-ceramic samples tended to grow and coalesce with the heat-treated temperature increasing.Furthermore,spheric nanosized grains appeared in PNS and BNS samples,while for SNS,the typical dendritic microstructure was found in the glass matrix.The dielectric properties of the glass-ceramics formed through controlled crystallization had a strong dependence on the phase assemblage,volume fraction and grain size of the crystalline dielectric phases.The measurements of dielectric constants and er-V curves exhibited that at annealed temperature of 900 ℃,the highest dielectric constant(～501,1 kHz) was found in PNS samples,respectively,while in the measured electric-field range from 0 kV · mm-1 to 15 kV · mm-1,the BNS samples showed the best electric-field stability of permittivity(<15%).