Anionic depolymerization transition in IrTe₂

Selenium substitution drastically increases the transition temperature of iridium ditelluride (IrTe₂) to a diamagnetic superstructure from 278 to 560 K. Transmission electron microscopy experiments revealed that this enhancement is accompanied by the evolution of nonsinusoidal structure modulations from q=1/5(101̄) to q=1/6(101̄) types. These comprehensive results are consistent with the concept of the destabilization of polymeric Te-Te bonds at the transition, the temperature of which is increased by chemical and hydrostatic pressure and by the substitution of Te with the more electronegative Se. This temperature-induced depolymerization transition in IrTe₂ is unique in crystalline inorganic solids.