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

我们建议利用最近落成的高能衍射光束线P21.1@PETRA III的新能力，从单晶衍射数据中确定TN = 30.8 K时Neel跃迁以下UO2的结构，测试碲中Bijvoet对强度的预测，并从两种化合物的热漫散射中获得热弹性刚度系数。能量（100 keV）的单晶衍射研究的UO2将允许我们提供准确的结构数据和测试假设的氧的位置在低温相。低温相的结构模型已经有40多年的历史了，它是由磁反射强度对散射角的依赖关系得出的。该模型从未针对高分辨率衍射数据进行过改进。与P21.1，我们将能够调查的结构变化发生在一级转变在30.8 K.With相同的实验设置，我们建议测试的Bijvoet对碲的相对强度的预测前所未有的精度。这将为确定单原子偏心晶体的绝对结构提供一种新的方法，通过热漫散射获得这两种化合物的热弹性系数，从而了解UO2在冷却过程中弹性刚度系数的软化以及碲在熔点之前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.