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(Zr_xTi_1−x)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.

烧绿石氧化物（A ₂ B ₂ O ₇）在许多技术应用中都很有趣，包括辐射损伤耐受性和作为离子导体。混合的烧绿石（包含两个A和/或两个B位阳离子）由于在该化学空间内可获得多种化学和构型自由度，因此为定制特性提供了更大的灵活性。在这里，我们研究了一个模型双烧绿石Gd ₂（Zr _x Ti _{1- x}）₂ O ₇中不同阳离子有序的相对稳定性，作为Zr含量x的函数。我们的结果表明，在存在一些非常特定的局部阳离子排列的情况下，由于大量的氧气弛豫位移，该系统中某些阳离子排序的组合物高度稳定，从而导致形成有序的“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倍配位环境的强烈化学偏好，而不是常规烧绿石结构中可用的6倍配位。随后，我们在131种其他烧绿石组合物中检查了这种排序的稳定性。