C_(60)分子在有序-无序和玻璃态相变间的取向概率与弛豫行为

ORIENTATIONAL POPULATION AND RELAXATION BEHAVIOR OF C_(60) MOLECULES BETWEEN ORDER-DISORDER PHASE TRANSITION AND GLASSY TRANSITION

用极限动力学模型研究了C60 分子在有序 无序相变和玻璃态相变温度区间取向角为 98°和 38°的取向概率与温度的关系 .计算结果在玻璃态相变点附近的 85K ,90K和有序 无序相变点的 2 6 0K分别与实验值相吻合 ,取向概率对实验值更精确的拟合及其对温度的二阶导数预言玻璃态相变点在 84K .导出了弛豫规律 ,其结果表明 :双能级的C60 分子从非平衡态到平衡态的弛豫行为与非指数因子 β有关 ,其总的弛豫时间决定于其中一个较短的弛豫时间 ,展宽指数形式保持不变 .讨论了KWW方程的非指数因子 β与分子间协同作用的关系 ,发现与双取向态间的能级差有关 ,计算值与实验结果相同 .

The site occupancies of orientational angle 98° and 38° of C 60 molecules versus temperature is investigated by extremal dynamic model in the temperature range between order\|disorder phase transition and glassy transition.The occupancy of orientational angle 38° calculated by the model are precisely coincident with reported experimental values at T=85 ?K,90?K and 260?K,respectively.The more precise agreement and second\|order differential to temperature of site occupancy predict that the glassy transition point is at 84?K.The relaxation process of two orientational states from non\|equilibrium deduced by the new model is related to the non\|exponent factor β in KWW equation,and overall relaxation of C 60 crystal is mainly attributed to the relaxation of the lowest energy level.Considering two energy levels and their energy difference,the calculated β value 0.9495 is near the experimental value 0.94±0.02.