Temperature-dependent high-energy diffraction and thermal diffuse scattering from UO2 and tellurium single crystals

我们建议利用最近建立的高能衍射线P21.1@Petra III的新能力，从单晶衍射数据确定在Tn=30.8K的Neel转变以下的UO2的结构，检验关于碲中Bijvoet对强度的预测，并从这两种化合物的热扩散散射中获得热弹性刚度系数。对UO2的低温高能(100keV)单晶衍射研究将使我们能够提供准确的结构数据，并验证关于低温相氧位置的假设。低温相的结构模型已经有40多年的历史了，它是根据磁反射强度与散射角的关系推导出来的。这一模型从未针对高分辨率的衍射数据进行过修正。在P21.1中，我们将能够以前所未有的精度研究在30.8K时发生的一级跃迁的结构变化。在相同的实验装置下，我们建议测试对碲中Bijvoet对的相对强度的预测。这将为确定单原子偏心晶体的绝对结构提供另一种方法。对于这两种化合物，热扩散散射将获得热弹性系数，使我们能够了解在UO2中冷却时弹性刚性系数的软化，以及直到熔点Te的链间和链内相互作用的变化。

We propose to exploit the new capabilities of the recently inaugurated high-energy diffraction beam line P21.1@PETRA III to determine from single crystal diffraction data the structure of UO2 below the Neel transition at TN = 30.8 K, to test a prediction concerning the intensities of Bijvoet pairs in tellurium and to obtain thermoelastic stiffness coefficients from thermal diffuse scattering from both compounds.Low temperature high-energy (100 keV) single crystal diffraction studies of UO2 will allowus to provide accurate structural data and test hypotheses on the oxygen position in the low temperature phase. The structural model for the low temperature phase is more than 40 year old and was derived from the dependence of the intensities of magnetic reflections on the scattering angle. This model has never been refined against high resolution diffraction data. With P21.1 we will be able to investigate the structural changes occurring at the first order transition at 30.8 K with unprecedented accuracy.With the same experimental set-up, we propose to test a prediction on relative intensities of Bijvoet pairs in tellurium. This would provide an alternative approach to determine the absolute structure of monatomic acentric crystals.For both compounds, thermoelastic coefficients will be obtained from thermal diffuse scattering, allowing us to understand the softening of elastic stiffness coefficients during cooling in UO2 and changes in the inter- and intrachain interactions in tellurium up to the melting point.