以氢氧化钾(KOH)和五氧化二铌(Nb2O5)为原料,通过微波水热法在200℃下合成出具有不同晶相、形貌的铌酸钾粉体(KNbO3).当KOH浓度在10～14mol/L时,可以制备出纯相的KNbO3粉体.X射线衍射(XRD)、场发射扫描电镜(FESEM)和透射电镜(TEM)分析可知,KOH浓度由10mol/L增大到15mol/L时,KNbO3粉体由斜方六面体变为正交相,再转变为四方相,对应的形貌也由金字塔状变为棒状,再转变为立方状.当KOH浓度增大到15mol/L时,出现了Nb2O5杂相.常压烧结制备了KNbO3陶瓷,其介电常数达到302,介电损耗为0.023,压电常数达到80 pC/N,平面机电耦合系数为0.17,机械品质因数为70,居里温度为420℃,正交-四方相变温度为223℃.
KNbO3 powders with different phases and morphologies were successfully synthesized through the reaction between KOH and Nb2O5 by microwave-assisted hydrothermal method at 200℃.Pure KNbO3 crystals were obtained when the concentration of KOH was maintained from 10mol/L to 14mol/L.According to the XRD,FESEM and TEM characterizations,it could be observed that as increasing the concentration of KOH from 10mol/L to 15mol/L,the KNbO3 phases changed from rhombohedral to orthorhombic then to tetragonal,and the corresponding morphology of the KNbO3 powders changed from pyramid-like to rod-like then to cubic-like.Some Nb2O5 phases were found when the concentration of KOH increased to 15mol/L.KNbO3 ceramics were sintered from the KNbO3 powders by conventional processing.The piezoeletric properties such as the piezoeletric constant d33,the relative permittivity ε33/ε0,the dielectric loss tanδ,the electromechanical coupling factors kp and the mechanical quality factor Qm of the sintered KNbO3 ceramics were 80 p℃/N,302,0.023,0.17,70,respectively.The tetragonal to orthorhombic and cubic to tetragonal phase transitions temperatures were 223℃ and 420℃,respectively.
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