Brincat Nicholas A, Parker Stephen C, Molinari Marco, Allen Geoffrey C, Storr Mark T
Department of Chemistry, University of Bath , Claverton Down, Bath, Avon, BA2 7AY, United Kingdom.
Inorg Chem. 2014 Dec 1;53(23):12253-64. doi: 10.1021/ic500791m. Epub 2014 Nov 18.
Uranium trioxide (UO3) is known to adopt a variety of crystalline and amorphous phases. Here we applied the Perdew-Burke-Ernzerhof functional + U formalism to predict structural, electronic, and elastic properties of five experimentally determined UO3 polymorphs, in addition to their relative stability. The simulations reveal that the methodology is well-suited to describe the different polymorphs. We found better agreement with experiment for simpler phases where all bonds are similar (α- and δ-), while some differences are seen for those with more complex bonding (β-, γ-, and η-), which we address in terms of the disorder and defective nature of the experimental samples. Our calculations also predict the presence of uranyl bonds to affect the elastic and electronic properties. Phases containing uranyl bonds tend to have smaller band gaps and bulk moduli under 100 GPa contrary to those without uranyl bonds, which have larger band gaps and bulk moduli greater than 150 GPa. In line with experimental observations, we predict the most thermodynamically stable polymorph as γ-UO3, the least stable as α-UO3, and the most stable at high pressure as η-UO3.
已知三氧化铀（UO₃）会呈现多种晶相和非晶相。在此，我们应用Perdew - Burke - Ernzerhof泛函 + U形式体系来预测五种通过实验确定的UO₃多晶型物的结构、电子和弹性性质，以及它们的相对稳定性。模拟结果表明，该方法非常适合描述不同的多晶型物。我们发现，对于所有键都相似的较简单相（α - 和δ - ），与实验结果的吻合度更好，而对于那些键合更复杂的相（β - 、γ - 和η - ），则存在一些差异，我们从实验样品的无序和缺陷性质方面对此进行了解释。我们的计算还预测了铀酰键的存在会影响弹性和电子性质。与不含铀酰键的相相比，含铀酰键的相往往具有更小的带隙和低于100 GPa的体模量，而不含铀酰键的相具有更大的带隙和大于150 GPa的体模量。与实验观察结果一致，我们预测热力学上最稳定的多晶型物为γ - UO₃，最不稳定的为α - UO₃，在高压下最稳定的为η - UO₃。
