Nd^(3+)掺杂钙钛锆石(Ca_(1-3x/2)Nd_(x)ZrTi_(2)O_(7))晶型转变行为的研究

Crystal Structure Evolution of Nd^(3+)-doped Zirconolite Ca_(1-3x/2)Nd_(x)ZrTi_(2)O_(7)Ceramics

采用高温固相反应法制备(Ca_(1-3x/2)Nd_(x)ZrTi_(2)O_(7))(0.0≤x≤0.5)系列钙钛锆石样品,借助X射线衍射(XRD)、拉曼光谱(Raman)、背散射电子像(BES)和能谱(EDS)分析,对其晶型转变行为进行了研究。结果表明:随着Nd^(3+)掺杂量的增加,钙钛锆石-2M(Zirconolite-2M)结构将向钙钛锆石-4M结构转变。x≤0.3时,随着Nd^(3+)掺杂量的增加,Ca_(1-3x/2)Nd_(x)ZrTi_(2)O_(7)样品主体仍为钙钛锆石-2M结构,但钙钛锆石-2M结构中Ca^(2+),Zr^(4+),Nd^(3+)的无序化程度增加;x=0.4时,部分钙钛锆石-2M结构发生重排(ZrO_(7)→ZrO_(8),TiO_(5)→TiO_(6))向→钙钛锆石-4M结构转变,伴随出现少量Zr-TiO_(4)相;Nd^(3+)取代Ca^(4+)量达到50%(x=0.5)时,钙钛锆石-2M结构彻底转变为→钙钛锆石-4M结构,且钙钛锆石-4M结构较-2M结构中Ti-O键长略微增加,Ca-O键长略微减小;同时出现一定量Zr_(1-x)Ti_(1+x)O_(4)固溶体相。样品晶粒的BES和EDS分析证实了这种晶型转变规律。

A series of compositions with general stoichiometry Ca_(1-3x/2)Nd_(x)ZrTi_(2)O_(7)(0.0≤x≤0.5)was prepared by high-temperature solid-state reaction of component oxides and characterized by powder XRD,Raman spectroscopy,backscattered electrons(BES)and EDS analyses.The crystal structure evolution of Nd^(3+)-doped Zirconolite Ca_(1-3x/2)Nd_(x)ZrTi_(2)O_(7)ceramics was elucidated with increasing concentration of Nd^(3+)(viz.x)in the compositions.Only major zirconolite-2M phase is observed when x≤0.3,while the disordering of the Ca^(2+),Zr^(4+)and Nd^(3+)cations in Zirconolite-2M lattice increases with increase in x.At higher substitution levels of Nd^(3+)ions(x=0.4),partly the zirconolite-2M structure rearrangement(ZrO_(7)→ZrO_(8),TiO_(5)→TiO_(6))occurs resulting in the formation of zirconolite-4M structure,in addition a small amount of zirconium titanate type phase(ZrTiO_(4))as a coexisting phase.All the zirconolite-2M structure converts into zirconolite-4M structure when x=0.5;moreover the Ti-O chemical bond is slightly elongated,on the contrary the Ca-O chemical bond is slightly shortened in zirconolite-4M structure;while a certain amount of zirconium titanate structure-type phase(Zr_(1-x)Ti_(1+x)O_(4))is found to coexist with zirconolite-4M phase.Further,the composition and microstructure of coexisting phases are verified by BES and EDS studies.