半化学法制备Pb(Fe2/3W1/3)O3陶瓷粉体的反应机理

铅系弛豫铁电陶瓷钨铁酸铅Pb(Fe2/3W1/3)O3(PFW)是一种重要的介电材料,具有较大的介电常数(8000)和较低的烧结温度(小于900℃),适用于制备低烧高介的多层陶瓷电容器犤1～4犦。在传统氧化物法合成PFW的过程中,易生成恶化介电性能的钨酸铅(PbWO4或Pb2WO5)或焦绿石相(Pb2FeWO6)等其他相犤3,4犦。尽管通过加入过量5%的Fe2O3可以消除这些其他相,但因含较多的变价铁离子(Fe3+和Fe2+)而产生介电老化的缺点犤5犦。虽然二次合成法被广泛用于制备铅系弛豫铁电陶瓷犤6犦,但对制备PFW陶瓷的效果并不明显,仍有少量的钨酸铅PbWO4存在,并且预烧…

Reaction Mechanisms of Pb(Fe2/3W1/3)O3 Powders Prepared by Semichemical Method

The mechanisms of Pb(Fe_2/3W_1/3)O₃(PFW) powders with pure perovskite phase prepared by semichemical method was proposed. The precursors were prepared by adding an aqueous Fe(NO₃)₃ solution rather than Fe₂O₃ to the alcoholic slurry of PbO and WO₃. The TG-DTG-DTA and XRD analysis showed that the mechanism in this method was different from those of the known columbite precursor method or conventional mixed oxide method. Fe(NO₃)₃ reacted with PbO to form a intermediate of Pb₂(NO₃)₂(OH)₂ and Fe(OH)₃ and/or Fe₂O₃ at milling and calcinations process. The activated PbO and Pb₃O₄ by the intermediate reacted with WO₃ to form PbWO₄, which reacted directly with nascent-state Fe₂O₃ to transform into a pyrochlore structure of Pb₂FeWO_6.5 at low calcining temperature. And then the pyrochlore phase progressively reacted with Fe₂O₃ to form perovskite PFW phase. Ad-ditionally, the effects of excess Fe₂O₃ on the formation of the perovskite PFW phase have been discussed.