Distortion-stabilized ordered structures in A2BB O7 mixed pyrochlores (A2BB O7 混合烧绿石中畸变稳定的有序结构)
Ghanshyam Pilania, Brian Puchala & Blas P. Uberuaga
npj Computational Materials 5:7 (2019)
doi:s41524-018-0144-1
Published online:14 January 2019
Abstract| Full Text | PDF OPEN
摘要:烧绿石氧化物（A2BBO7 ）在许多技术应用中都很有趣，包括耐辐射损伤和作为离子导体。混合烧绿石（包含两个A和/或两个B位阳离子）由于在该化学空间中可获得的化学和构型自由度不同，为定制性能提供了更大的灵活性。本研究以Zr/Ti的含量作为变量，考察一种双烧绿石Gd2(ZrxTi1x)2O7模型中不同阳离子排序的相对稳定性。我们的结果表明，在某些特定的局部阳离子排列下，由于氧弛豫位移大，该系统中的某些阳离子有序成分高度稳定，从而形成有序的“双”烧绿石结构。这些异常氧弛豫的起源可追溯到局部阳离子对称性和Zr原子对采用7配位环境的强化学偏好，而不是常规烧绿石结构中的6配位构型。随后，我们在131个其它烧绿石成分中考察了这类有序结构的稳定性。我们的研究意义与系统中所观察到的组成离子电导率有关，并与之前报道的实验结果有关。
Abstract:Pyrochlore oxides (A2B2O7) are interesting for a number of technological applications, including radiation damage tolerance and as ionic conductors. Mixed pyrochlores—containing two A and/or two B site cations—provide even more flexibility for tailoring properties owing to the diverse chemical and configurational degrees of freedom accessible within this chemical space. Here, we examine relative stability of different cation orderings in one model double pyrochlore Gd2(ZrxTi1x)2O7, as a function of Zr content x. Our results show that, in the presence of some very specific local cation arrangements, certain cation-ordered compositions in this system are highly stabilized as a result of large oxygen relaxation displacements, leading to the formation of an ordered ‘double’ pyrochlore structure. The origins of these anomalous oxygen relaxations are traced back to both the local cation symmetry and a strong chemical preference of Zr atoms towards adopting a 7-fold coordination environment, as opposed to a 6-fold coordination available in a regular pyrochlore structure. Subsequently, we examine the stability of this type of ordering in 131 other pyrochlore compositions. Implications of our findings are discussed in relation to the observed composition-dependent ionic conductivity in these systems and connections with previously reported experimental findings are made.
Editorial Summary
Mixed pyrochlore: an ordered structure with stable distortion（混合烧绿石：畸变稳定的有序结构）
该研究在混合Gd2Ti2O7–Gd2Zr2O7 烧绿石结构中发现了新型低能有序结构。来自美国洛斯阿拉莫斯国家实验室的Ghanshyam Pilania和Blas P. Uberuaga等，使用密度泛函理论（DFT），以Zr含量x的作为变量，研究了一种双烧绿石Gd2(ZrxTi1x)2O7中不同阳离子排序的相对稳定性。他们的结果表明，在某些特定的局部阳离子排列下，由于氧弛豫位移大，该系统中的某些阳离子有序成分高度稳定，从而形成有序的“双”烧绿石结构。这些异常氧弛豫的起源可追溯到局部阳离子对称性和Zr原子对采用7配位环境的强化学偏好，而不是常规烧绿石结构中的6配位构型。混合烧绿石中潜在的有序结构开辟了定制这些系统性质的新途径，扩展了这类化合物的功能空间。双烧绿石这一研究可能与其组成离子的电导率有关，并与之前报道的实验结果有关。
A novel low-energy ordered structure of mixed Gd2Ti2O7–Gd2Zr2O7 pyrochlore was reported. Ghanshyam Pilania and Blas P. Uberuaga from Los Alamos National Laboratory and Brian Puchala used density functional theory (DFT) to examine relative stability of different cation orderings in one model double pyrochlore Gd2(ZrxTi1x)2O7, as a function of Zr content x. Their results show that, in the presence of some very specific local cation arrangements, certain cation-ordered compositions in this system are highly stabilized as a result of large oxygen relaxation displacements, leading to the formation of an ordered ‘double’ pyrochlore structure. The lowest energy structures are stabilized by an oxygen relaxation that allows for 7-fold coordination of some of the Zr cations in these structures, rather than 6-fold in the conventional pyrochlore structure. The potentially ordered structure of mixed pyrochlore opens up new avenues for customizing the properties of these systems, extending the functional space of such compounds. The study of double pyrochlore may be related to the conductivity of its constituent ions and is related to the previously reported experimental results.
沪公网安备 31010502006565号
