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

利用拨款，我们更新了大约二十年前安装在实验室的扫描绝热量热计的部分电子模块。我们用该量热计测量了大于液相温度的块状试样（~ 0.1 mol）的比热。为了补充上述测量，在熔化温度以下的过冷区域用调制方法测量了一个小样品（~ 0.005摩尔）密封在毛细管熔融石英池中。结合这两个数据，我们可以得到800℃范围内熔融金属和合金的比热。我们测量了富Te共晶成分（15 at）周围Ge-Te合金的比热。% Te)，在熔融合金中表现出最急剧的转变，并经历持续的结构变化。同时，用高能γ射线衰减法测定了声速，得到了声速密度。因此，我们可以确定所有的热力学响应函数，从而更好地表征Ge-Te体系的结构变化。主要结果有：1。在共晶组分Ge_<15>Te_<85> 2处，交叉温度T*（比热随温度变化的峰值）达到最大值。在相同的成分下，比热的宽度变得最窄。结果表明，共晶Ge-Te合金的组织变化不会引起浓度波动，属于同晶型。进一步提出了比热宽度可解释为交叉温度T*波动的新思路。(j . Non-Cryst。为了研究原子尺度上的结构演化，我与dr。C. Bergman （L2MP CNRS，马赛）和C. Bichara （CRM2C CNRS，马赛）。结果表明，液体的结构变化主要表现在锗原子的第一邻壳层发生了修饰，而peerls畸变机制在结构变化中起着重要作用。(理论物理。Rev. B. 67 (2003) 104202-104202-5

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