摘要
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_(x)Ti_(1−x))_(2)O_(7),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.
基金
The work was performed at the Los Alamos National Laboratory(LANL),an affirmative action equal opportunity employer,operated by Los Alamos National Security,LLC,for the National Nuclear Security Administration of the U.S.DOE under contract DE-AC52-06NA25396
Computational support for this work was provided by LANL’s high performance computing clusters.
