Infinitely Adaptive Transition-Metal Ordering in Ln2O2MSe2?Type Oxychalcogenides

A number of Ln2O2MSe2 (Ln = La and Ce; M = Fe, Zn, Mn,

and Cd) compounds, built from alternating layers of fluorite-like [Ln2O2]2+

sheets and antifluorite-like [MSe2]2? sheets, have recently been reported in the

literatures. The available MSe4/2 tetrahedral sites are half-occupied, and

different compositions display different ordering patterns: [MSe2]2? layers

contain MSe4/2 tetrahedra that are exclusively edge-sharing (stripe-like),

exclusively corner-sharing (checkerboard-like), or mixtures of both. This paper

reports 60 new compositions in this family. We reveal that the transition-metal

arrangement can be systematically controlled by either Ln or M doping, leading

to an “infinitely adaptive” structural family. We show how this is achieved in

La2O2Fe1 ? xZnxSe2, La2

O2Zn1 ? xMnxSe2, La2

O2Mn1 ? xCdxSe2 ,

Ce2O2Fe1 ?xZnxSe2, Ce2

O2Zn1?xMnxSe2, Ce2

O2Mn1 ?xCdxSe2 ,

La2?yCeyO2FeSe2, La2?yCeyO2ZnSe2, La2?yCeyO2MnSe2, and La2?yCeyO2CdSe2

solid solutions.