Synthesis Of A₂B₂O₇ Rare-earth Complex Oxide And Pyrochlore Structure

A₂B₂O₇ rare-earth complex oxide comprises of a number of different types; because of its qualified characteristics,it has drawn attention from many scholars both home and abroad in recent years.But there is still no detailed and systematic research on the structure determination and evolution relationship of this set of oxides;as its stability and characteristics are different when structure differs,research on its structure and evolution will help to understand and study the characteristics and structure stability of mineral admixtures and the stability of structure is very important to utilization value in industry.The paper will study the A₂B₂O₇(A=REE rare earth element,B= Ti,Zr) rare-earth complex oxid.By adopting high- temperature solid phase method,we first obtain precursors after keeping heat for 2h at 1000,then synthesize target product after calcinations at 1280 for 2h.Meanwhile,by improving a new soft chemistry method, we obtain precursors after keeping heat for 2h at 600,then synthesize target product after calcinations at 1200 for 2h.Soft- chemistry method is chosen for follow- up experiments.Two types of raw materials,REE₂O₃ and REE(NO₃)₃.6H₂O,are selected in this article to conduct experiments respectively.Analyzing the particle micro topography through SEM,the resultant grain synthesized from REE₂O₃ is around 1-2um in size and shows clear grain boundary;while the resultant grain from REE(NO₃)₃.6H₂O is＜1μm in size,the grain boundary is no longer obvious,the grains have sufficient contacts and better melting effect,and it is easy to obtain single crystal through high temperature melting method.Through research on a number of single crystal cultivation methods,high temperature melting process is finally adopted,after choosing appropriate parameters to cultivate Sm₂Ti₂O₇ and Gd₂Ti₂O₇ single crystal for structure determination.Through characterization methods like XRD powder diffraction,SEM,single crystal structure analysis,electron probe and fluorescence emission spectrum etc,it shows that,A₂B₂O₇(A =REE,B= Ti,Zr) Ti(VIZ A₂Ti₂O₇) rare earth composite oxides can be obtained as La₂Ti₂O₇ & Nd₂Ti₂O₇ which are monoclinic system,and belong to space group P2₁;while other Ti(VIZ A= Sm- Lu) products are all pyrochlore structure,cubic crystal system and belong to space group Fd-3m;in Zr products(VIZ A₂Zr₂O₇),when A= La,Nd,Sm,Eu & Gd,it forms pyrochlore structure,cubic crystal system and belongs to space group Fm-3m;while when A=Tb-Lu,it forms fluorite structure,cubic crystal system and belong to space group Fm-3m;and as atomic number increases and atomic radius decreases,cell parameters also decreases.And the fluorite structure of Lu₂Zr₂O₇ has never seen before.