GeO2 vs SiO2: Glass transitions and thermodynamic properties of polymorphs
GeO2 vs SiO2: Glass transitions and thermodynamic properties of polymorphs
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GeO2 与 SiO2：多晶型物的玻璃化转变和热力学性质
DOI：
10.1007/bf00209228
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发表时间：
1990
影响因子：
1.4
通讯作者：
P. Richet
中科院分区：
文献类型：
--
作者：
P. Richet
相对焓的测量已作出的六方晶系，四方晶系，玻璃和液相的GeO 2。的玻璃化转变是非常敏感的杂质含量，与Tg范围从980 K的纯产品的780 K的锂掺杂的样品与0.06摩尔%的锂。由于玻璃化转变温度较低，在约5%的Tg下的相对Cp变化随着杂质含量的增加而增加。高于298 K的推导出的热容量是类似的所有形式，与略高的值为非晶相和两个Cp交叉在400和1000 K之间的六方和tetraorthane修改。对于GeO 2和SiO2，配位状态显著影响Cp和低于300 K的熵，其中四方晶系的性质比六方晶系的性质低得多，即，对于GeO 2和SiO2，S298分别为39.7和55.3 J/mole K以及27.8和41.4 J/ mole K。柯石英和方石英的高温Cp可能类似于低压SiO2形式的Cp。最后，这些结果，低温Cp的数据和解决方案的测量已被用来获得一组一致的GeO 2修改的热力学性质。
Relative-enthalpy measurements have been made on the hexagonal, tetragonal, glass and liquid phases of GeO2. The glass transition is very sensitive to the impurity content, with a Tg ranging from 980 K for a pure product to 780 K for a Li-doped sample with 0.06 mol % Li. The relative Cp change at Tg of about 5% increases with the impurity content as a result of lower glass transition temperatures. Above 298 K the derived heat capacities are similar for all forms, with slightly higher values for the amorphous phases and two Cp cross-overs at 400 and 1000 K between the hexagonal and tetragonal modifications. For both GeO2 and SiO2 the coordination state markedly affects Cp and the entropy below 300 K, where the properties are much lower for the tetragonal than for the hexagonal modifications, i.e., S298 = 39.7 vs 55.3 J/mole K and 27.8 vs 41.4 J/ mole K for GeO2 and SiO2, respectively. The high-temperature Cp's of coesite and stishovite are likely similar to those of the low-pressure SiO2 forms. Finally, these results, low-temperature Cp data and enthalpy-of-solution measurements have been used to derive a consistent set of thermodynamic properties for the GeO2 modifications.