MLnBO_4陶瓷中K_2NiF_4型层状钙钛矿结构的稳定性

通过固相反应法制备了MLnBO_4(M=Ba,Sr,Ca;Ln=La,Nd,Sm,Y;B=(Zn0.5Ti0.5),(Mg_(0.5)Ti_(0.5)))陶瓷粉末,使用X射线衍射仪(XRD)分析其相组成,并结合文献中B位为Ga和Al时的结果,探讨了MLnBO_4中K_2NiF_4型层状钙钛矿结构的稳定性。当M~(2+)和B~(3+)固定时,K_2NiF_4型结构的稳定性随钙钛矿层许容因子t偏离1程度的增加而降低;但当M~(2+)或B~(3+)改变时,两者之间并无直接联系。而考虑M~(2+)、Ln~(3+)、B~(3+)离子半径的对比时,则发现K_2NiF_4型结构均出现在以r(M~(2+))/r(Ln~(3+))=1.1、r(Ln~(3+))/r(B~(3+))=2为中心的一定范围内。因此,用M~(2+)、Ln~(3+)、B~(3+)离子半径的对比衡量MLnBO_4中K_2NiF_4型层状钙钛矿结构的稳定性远较用钙钛矿层的许容因子更可靠,这对于相关材料的设计和开发具有重要意义。

Stability of K2NiF4-Type Layered Perovskite Structure in MLnBO4 Ceramics

MLnBO4(M=Ba,Sr,Ca;Ln=La,Nd,Sm,Y;B=(Zn0.5Ti0.5),(Mg0.5Ti0.5)) ceramic powders were prepared by solid state reaction method,and the phase constitution of the products was analyzed by XRD (X-ray diffraction).Combining with the results for B=Ga and Al from the literatures,the stability of K2NiF4-type layered perovskite structure in MLnBO4 ceramics was discussed.For certain M2+ and B3+ ions,K2NiF4-type structure became unstable with the deviation of tolerance factor of perovskite layer (t) from 1.For some differentM2+ and B3+ ions,however,no direct relationship could be observed between them.On the other hand,when considering the ion radii differences of M2+ 、Ln3+ and B3+,it was observed that K2NiF4-type structure only existed in an area that was centered at r(M2+)/r(Ln3+) =1.1 and r(Ln3+)/r(B3+) =2.Therefore,it is much more reliable to estimate the stability of K2NiF4-type layered perovskite structure in MLnBO4 ceramics by comparing the ion radii of M2+,Ln3+ and B3+ rather than by the tolerance factor of perovskite layer.These findings are important for the design and development of relevant materials.