Structural aspects of layered double hydroxides

Layered double hydroxides (LDHs) have been known for a considerable time and have been widely studied. The basic features of their structure, involving positively charged brucite-like layers together with charge-balancing anions and water in interlayer galleries are well understood, but some detailed aspects of their structure have been the subject of controversy in the literature. In this article we review the wide range of experimental and theoretical studies of the structure of LDHs, highlighting areas of consensus and currently unresolved issues. We focus on the range of composition for which LDHs may be formed, possible layer stacking polytypes, arrangement of guest species in the interlayer galleries and the extent of order-disorder phenomena, both long-range and short-range, in the layers and interlayer galleries.