Phase transition of nano Bi_2O_3-based materials at high temperature

With A.R.Bi(NO_3)_3·5H_2O and Y(NO_3)_3·6H_2O as raw materials,nano Bi_2O_3 and Bi_2O_3-Y_2O_3 (75mol%Bi_2O_3+25mol%Y_2O_3) powders were prepared and the average grain sizes were less than 40 and 30nm, respectively.The study results of TG-DTA,high temperature XRD and high temperature Raman on phase tran- sition behave of these powders showed that metastable state nanometerβ-Bi_2O_3 transformed into stableα-Bi_2O_3 at low temperature (420℃) first,thenα-Bi_2O_3 transitioned intoδ-Bi_2O_3 at 720℃during the heated process; during the cooled process,phase transformation process wasδ→β→α,because nano-Bi_2O_3 has higher activity which lead to lower transition temperature than micron-Bi_2O_3.The solid solution reaction of Y_2O_3 andβ-Bi_2O_3 started at lower temperature (400℃) during the process of heated mixed nano Bi_2O_3-Y_2O_3 powder,b-Bi_2O_3 had almost completely transformed intoδ-Bi_2O_3 at 500℃and the solid solution reaction turned to end.Theβ→δphase transformation temperature was lowered obviously by doping of Y_2O_3.