Heat Capacity Changes at the Glass Transition in Mixed‐Alkali Tellurite Glasses
Heat Capacity Changes at the Glass Transition in Mixed‐Alkali Tellurite Glasses
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DOI：
10.1111/j.1151-2916.1997.tb02988.x
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发表时间：
2005-01
影响因子：
3.9
通讯作者：
T. Komatsu;T. Noguchi;R. Sato
中科院分区：
文献类型：
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作者：
T. Komatsu;T. Noguchi;R. Sato
测量了 (20-x)Li2O-xNa2O-80TeO2 的混合碱亚碲酸盐玻璃在玻璃化转变时的热容变化 (ΔCp)，该玻璃表现出不同的脆性，具体取决于 Na2O/Li2O 的比例，已测量以获得有关亚碲酸盐玻璃或具有脆性特性的过冷液体的结构的更详细信息。在所有样品的玻璃化转变过程中都可以清楚地观察到 Cp 的大幅增加。无论 Na2O/(Na2O+Li2O) 比率如何，玻璃和过冷液体在玻璃化转变温度 Tg 下的热容值（分别为 Cpg 和 Cpe）和 ΔCp（等于 Cpe-Cpg）几乎相同，表明在 Tg 下 Cp 不存在明显的混合碱效应。 200℃时的Cpg、300℃时的Cpe、Tg时的ΔCp的值分别为}75、120、45J·(mol·K)-1。玻璃态热容与过冷液态热容之比，即Cpe/Cpg为1.6；这个大的值表明(20-x)Li2OxNa2O80TeO2系统应属于易碎液体类别。有人认为，TeO4三方双锥体和TeO3三方锥体的结构单元之间的连接较弱，因此中间结构随着温度的升高而变化很大，从而导致脆性。不同种碱离子混合引起的脆性变化不能通过ΔCp检测出来（即混合碱对热力学脆性没有影响）；然而，这是从 } }Tg 下的粘度行为观察到的（即存在混合碱对动力学脆性的影响）。
The heat capacity changes (ΔCp) at the glass transition in mixed-alkali tellurite glasses of (20-x)Li2O-xNa2O-80TeO2 that show different fragilities, depending on the Na2O/Li2O ratio, have been measured to obtain more-detailed information on the structure of tellurite glasses or supercooled liquids with a fragile character. A large increase in Cp is clearly observed at the glass transition in all the samples. The values of the heat capacity of glasses and supercooled liquids (Cpg and Cpe, respectively) and ΔCp (equal to Cpe-Cpg) at the glass transition temperature, Tg, are almost the same, irrespective of the Na2O/(Na2O+Li2O) ratio, indicating the absence of a clear, mixed-alkali effect on Cp at Tg. The values of Cpg at 200°C, Cpe at 300°C, and ΔCp at Tg are } 75, 120, and 45 J·(mol·K)−1, respectively. The ratio of the heat capacity of the glassy state to the heat capacity of the supercooled liquid state, i.e., Cpe/Cpg, is 1.6; this large value indicates that the (20-x)Li2OxNa2O80TeO2 system should be included in the category of fragile liquids. It has been suggested that the structural units of TeO4 trigonal bipyramid and TeO3 trigonal pyramid are weakly connected to each other and, thus, the intermediate structure varies largely as the temperature increases, which leads to a fragile character. The change in the fragility that is caused by the mixing of dissimilar alkali ions is not detected through ΔCp (i.e., there is no mixed-alkali effect on thermodynamic fragility); however, it is observed from the viscosity behavior at } }Tg (i.e., the presence of the mixed-alkali effect on kinetic fragility).