钒磷玻璃结构弛豫的DMA测量研究

The structural relaxation in vanadium phosphate glass studied by DMA

玻璃材料发生屈服和玻璃-液体转变(GLT)之前发生的缓慢结构演化和微观局域暗流的机理至今尚未完全清晰.本文采用动态热机械分析仪系统测量了钒磷二元体系玻璃(V_2O_5-P_2O_5)趋向于玻璃化转变点T_g的动态机械弛豫谱和应力松弛谱,在T_β~483 K和T_ρ~543 K p附近发现了类金属玻璃的α和β结构弛豫和应力松弛行为,结果表明,其与纳米局域钒磷暗流结构的缓慢流动有关.实验首次发现了V_2O_5-P_2O_5玻璃的β弛豫的峰高与驰豫速率符合一定的线性对数关系,即ln(Δ)∞μ-ln(v);基于Wang等人提出的唯像理论模型和稳态流体动力学理论给出了合理的物理图像解释;实验和理论良好符合,进一步证明了V_2O_5-P_2O_5玻璃体系中存在纳米局域钒磷暗流结构及其演化行为的结论.并采用KWW方程的非指数因子β_(KWW)把T_g附近结构演化划分为3个阶段:(1)β_(KWW)<0.1 ,纳米局域磷钒分子流体单元区;(2)0.1<β_(KWW)<0.5 ,纳米局域磷钒微晶暗流区;(3)β_(KWW)>0.5 ,宏观流动区.

The mechanism of structure evolution and microscopic hidden flow in glasses before yield and glass-to-liquid transition（GLT） remains unclear. In this work, the dynamic mechanical relaxation and stress relaxation spectra of vanadium-phosphate binary glass （V2O5-P2O5） when approaching the glass transition temperature Tg were investigated by using the dynamic mechanical analysis （DMA）. The β and α relaxation behaviors, occurring respectively at Tβ- 483 K and Tp-543 K and quite similar to those observed in the metal glass systems, were observed, which indicated the occurrence of the slowing-down microscopic localized flow in the investigated vanadium-phosphate glasses. This was further verified by the experimental observation and theoretical prediction of the linear logarithmic relation between the peak height of the β relaxation and the relaxation rate, i.e. ln（A）oc-ln（v）. Furthermore, three stages during the structural evolution of the β and α relaxation in vanadium-phosphate glasses were observed from the temperature dependent curve of the non-exponential factor of βKww obtained by the Kohlrausch-Williams-Watts （KWW） fitting： （I） βKww〈0.1, the region dominated by the localized flow units of the nano vanadium-phosphate molecular; （Ⅱ） 0.1 〈flKWW〈0.5, the region of localized hidden flow dominated by the nano vanadium-phosphate microcrystalline; （Ⅲ） βKww〉0.5, the region of macroscopic flow.