Application of specific heat measurements to the study of structural changes and concentration fluctuations in the molten semiconductors

利用这笔赠款，我们更新了大约20年前安装在实验室的扫描绝热量热计的一些电子模块。我们用这种量热计测量了大质量样品（~ 0.1摩尔）在液相线温度以上的比热。为了补充上述测量，使用密封在毛细管熔融石英池中的小样品（~ 0.005摩尔），用调制方法测量低于熔融温度的过冷区域中的比热。结合这两个数据，我们可以得到熔融金属和合金在800℃以下的较宽温度范围内的比热。我们测量了富Te共晶组份（15 at.%）附近Ge-Te合金的比热Te），它显示了经历持续结构变化的熔融合金中最急剧的转变。同时，用高能γ射线衰减法测得了密度，并测量了声速。我们可以确定所有的热力学响应函数. ...更多信息 ns表征Ge-Te系统的结构变化，因此。主要结果如下：1.作为温度函数的比热峰值所表示的交叉温度T* 在低共熔成分Ge_Te_2处达到最大值<15><85>。从这些结果可以看出，共晶Ge-Te合金中的结构变化并不引起浓度波动，因此它是一种同构型。此外，我们提出了一个新的想法，比热的宽度可以解释为在交叉温度T* 的波动。(J.非晶体固体312-314（2002）212）为了研究原子尺度上的结构演化，我与C. Bergman（L2 MP CNRS，马赛）和C. Bichara（CRM 2C CNRS，马赛）。结果表明，Ge原子的第一近邻壳层结构发生了变化，Peierls形变机制在这种结构变化中起着重要作用。（物理修订版B。67（2003）104202-104202-5））减

Using the grant, we have renewed some of the electronic modules of the scanning adiabatic calorimeter installed in the laboratory about two decades ago. We use this calorimeter to measure the specific heat of massive specimen (~ 0.1 mole) above the liquidus temperature. To complement the above measurements, the specific heat in the super-cooled region below the melting temperature is measured with the modulation method using a small specimen (~ 0.005 mole) sealed in capillary molten quartz cell. By combining both data, we can obtain the specific heat of molten metals and alloys in the wide range of temperature up to 800℃.We measured the specific heat of Ge-Te alloys around the Te rich eutectic composition (15 at.% Te) that shows the most sharp transition among molten alloys undergoing continues structural change. In the meantime, we obtained the density by the high energy γ-ray attenuation method and measured the sound velocity. We could determine all the thermodynamic response functio … More ns characterizing the structural changes in the Ge-Te system, therefore. Main results are:1. the crossover temperature T* indicated by a peak in the specific heat as a function of temperature reached a maximum at the eutectic composition, Ge_<15>Te_<85>.2. the width of the specific heat becomes narrowest at the same composition.From these results we showed that the structural change in the eutectic Ge-Te alloy does not induce the concentration fluctuations and therefore it is a kind of isomorphic type. Further we proposed a new idea that the width of the specific heat can be interpreted as fluctuations in the crossover temperature T*. (J. Non-Cryst. Solids 312-314 (2002) 212)To investigate the structural evolution in the atomic scale, I analyzed the neutron diffraction data together with the above-mentioned thermodynamic data in collaboration with Drs. C. Bergman (L2MP CNRS, Marseille) and C. Bichara (CRM2C CNRS, Marseille). It is shown that the structural change undergone by the liquid mainly consists in a modification of the first-neighbor shell of the Ge atoms and the Peierls distortion mechanism plays an important role in the structural change. (Phys. Rev. B. 67 (2003) 104202-104202-5)) Less