High-Pressure Synthesis and Order-Disorder Transition of Layered Oxytelluride Ba 2 ZnO 2 Ag 2 Te 2 .

A layered oxytelluride, Ba 2 ZnO 2 Ag 2 Te 2 , which consists of alternating stacks of ZnO 2 and Ag 2 Te 2 layers with Ba ions in between, has been synthesized via high-pressure reaction. At ambient temperature, it contains discrete [ZnO 2 ] 2- linear units similar to Ba 2 ZnO 2 Ag 2 Se 2 ( Cmca ), meaning that the unusual linear coordination around zinc center is stable even when a greater tensile strain is applied by the sandwiched Ag 2 Te 2 layers in addition to barium ions. Upon heating, this compound undergoes an order-disorder phase transition from orthorhombic ( Cmca ) to tetragonal ( I 4/ mmm ) system at 350 K, transforming the ZnO 2 lattice in linear coordination into a lattice with disordered oxide ions, suggesting the presence of cis / trans coordination coexistence as well as correlated disorder.