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

两种不同的非晶锗碲化物（GCT）目前被认为具有巨大的技术应用潜力。虽然Cux+yGe20 xTe80-y（0≤x≤20,0≤y≤10）表现出优异的热电性能，但gct相图中(FeTe) - (CuTe)准二元线上的混合物被确定为相变材料（PCM），是非易失性数字数据存储应用的候选材料。这两个材料组在GCT相图中位置相对较近，但随着cu浓度的变化，观察到的热稳定性完全不同。当不断添加铜时，热电材料（TE）的结晶温度急剧下降，而在相对较高的cu浓度下，pcm的结晶温度显著上升，最终开始下降，但始终保持在TE值以上。特别是对于te系统，高结晶温度意味着高热稳定性，对于它们在技术应用中的使用是可取的。这种不同行为的起源尚不清楚。一般来说，决定多组分玻璃结晶温度和相关热稳定性的原因仍然广泛未知，尽管这种理解对于技术玻璃的热优化是非常需要的。在完全不同的cu浓度下，这两种系统只进行了一项结构研究，都是用EXAFS进行的。只获得了化学短程顺序的信息，对热稳定性和其他物理性质没有显著的认识。在项目要求中，我们希望系统地研究两种体系的微观结构随cu含量的增加而变化，以确定不同稳定性行为的结构来源。为此，我们将反常x射线散射（AXS）与反向蒙特卡罗模拟相结合，这允许在化学短程顺序上获得原子特定的结构信息，但也可以在更大的长度尺度上获得。这允许表征化学有序短程结构之间的结构相关性。我们将研究这种结构相关性，或者更具体地说，与相应晶体相的相似性是否会影响非晶相的稳定性。这是由先前的无定形锗锑碲组合物的研究结果表明。如果这种关系能够得到验证，这将是对非晶多组分体系热稳定性普遍理解的重要的第一步，因此对于开发新的非晶材料也具有重要的指导意义。

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.