Structures, Physical Properties, and Chemistry of Layered Oxychalcogenides and Oxypnictides

Abstract

A series of layered oxychalcogenide and oxypnictide solids is described that contain oxide layers separated by distinct layers, which contain the softer chalcogenide (S, Se, Te) or pnictide (P, As, Sb, Bi) anions. The relationships between the crystal structures adopted by these compounds are described, and the physical and chemical properties of these materials are related to the structures and the properties of the elements. The properties exhibited by the oxychalcogenide materials include semiconductor properties, for example, in LaOCuCh (Ch = chalcogenide) and derivatives, unusual magnetic properties exhibited by the class Sr 2MO 2Cu 2-deltaS 2 (M = Mn, Co, Ni), and redox properties exhibited by the materials Sr 2MnO 2Cu 2 m-0.5 S m+1 ( m = 1-3) and Sr 4Mn 3O 7.5Cu 2Ch 2 (Ch = S, Se). Recent results in the oxychalcogenide area are reviewed, and some new results on the intriguing series of compounds Sr 2MO 2Cu 2-deltaS 2 (M = Mn, Co, Ni) are reported. Oxypnictides have received less recent attention, but this is changing: a new frenzy of research is underway following the discovery of high-temperature superconductivity (>40 K) in derivatives of the layered oxyarsenide LaOFeAs. The early results in this exciting new area will be reviewed.