Microscopic Structure Studies to understand the Thermal Stability of Amorphous Copper-Telluride-Phases

两组不同的非晶态Ge-Cu-Telluride(GCT)目前被认为具有可能的技术应用的巨大潜力。虽然Cux+yGe20xTe80-y(0≤x≤20，0≤y≤10)化合物表现出优异的热电性能，但在GCT相图中位于(FeFe)-(CuT)准二元线上的混合物被鉴定为相变材料，是非易失性数字数据存储应用的候选对象。这两个物质群在GCT相图中位置相对较近，但随着铜离子浓度的不同，观察到了根本不同的热稳定性。当不断添加铜时，热电材料的结晶温度(TE)显著下降，而相变材料的结晶温度在相对较高的铜浓度下显著上升，最终开始下降，但始终保持在TE值以上。特别是对于TE体系，高的结晶温度意味着高的热稳定性，这将是它们在技术应用中的理想选择。这种不同行为的起源尚不清楚。更广泛地说，决定多组分玻璃析晶温度和相关热稳定性的原因总体上仍然是未知的，尽管这样的理解对于工业玻璃的热优化是非常必要的。对于每个系统，目前只有一种结构研究，两种系统都是在完全不同的铜浓度下用EXAFS进行的。只获得了关于化学短程有序性的信息，没有获得关于热稳定性或其他物理性质的显著认识。在所要求的项目中，我们希望系统地研究这两个体系随着铜含量的增加而微观结构的变化，以确定不同稳定性行为的结构根源。为此，我们将使用反常X射线散射(AXS)和反向蒙特卡罗模拟相结合，这允许获得化学短程有序的原子特定的结构信息，但也可以在更大的长度尺度上。这允许表征化学有序短程结构之间的结构相关性。将研究这种结构相关性，或者更具体地说，所产生的与相应晶相的相似性是否影响非晶相的稳定性。先前对非晶态Ge-Sb-Te组分的研究结果表明了这一点。如果这种关系能够得到证实，这将是朝着普遍理解非晶态多组分体系热稳定性迈出的重要的第一步，因此对于定向开发新的非晶态材料也是非常重要的。

Two different groups of amorphous Ge-Cu-Tellurides (GCT) are currently regarded to comprise great potential for possible technical applications. While compositions Cux+yGe20 xTe80-y (0≤x≤20, 0≤y≤10) show excellent thermoelectric properties, mixtures on the (FeTe) – (CuTe) quasi-binary line in the GCT-phase diagram, were identified as Phase-Change-Materials (PCM) and are candidates for non-volatile digital data storage-applications. These two material groups are located relatively close to each other in the GCT phase diagram yet, a fundamentally different thermal stability is observed with varying Cu-concentration. While the crystallization temperature of the thermoelectric materials (TE) drops strongly when Copper is constantly added, a significant rise is observed in the PCMs up to relative high Cu-concentrations, where it finally starts dropping however remaining always above the TE-values. Especially for the TE-systems a high crystallization temperature, implying high thermal stability, would be desirable for their use in technical applications. The origin for this different behavior is yet unidentified. More generally, the reasons determining crystallization temperature and related thermal stability in multi component glasses in general are still widely unknown although such an understanding is highly desired for the thermal optimization of technical glasses.Only one structural study yet exists for each of the systems, both carried out with EXAFS, at completely different Cu-concentrations. Only information about the chemical short range order was obtained and no notable cognition on the thermal stability or other physical properties was acquired. In the requested project we would like to systematically study the variation of the microscopic structure of both systems with rising Cu-content to identify the structural origin for the different stability behavior. For this we will us Anomalous X-ray scattering (AXS) combined with Reverse Monte Carlo simulations, which allows to gain atom-specific structural information on the chemical short range order but also on larger length scales. This allows characterizing structural correlations between chemically ordered short range structures. It will be investigated if such structural correlations, or even more specific the resulting similarities to the corresponding crystal phase, affects the stabilities of the amorphous phases. This is indicated by results obtained from a preceding study on amorphous Ge-Sb-Te-compositions. It would be an important first step towards a universal understanding of the thermal stability in amorphous multi component systems if such a relation could be verified and therefore also highly important for directed progress in the development of new amorphous materials.