Thermal stability of the layered modification of Cu_0.5ZrTe₂ in the temperature range 25-900 °C

The thermal stability of the layered modification of the Cu_0.5ZrTe₂ polycrystalline intercalation compound, synthesized at room temperature, has been studied in the temperature range 25-900 °C. A change in the occupation of the octahedral and tetrahedral coordinated sites in the interlayer space of the zirconium ditelluride was observed using in-situ time-resolved synchrotron X-ray powder diffraction experiments. The formation of the rhombohedral CuZr₂Te₄ phase, which is stable in the temperature range 300-700 °C, has been observed. The copper intercalation at room temperature leads to the formation of a phase in which the Cu atoms occupy only octahedral sites in the interlayer space. At temperatures above the decay temperature of the rhombohedral CuZr₂Te₄, a layered phase with Cu atoms uniformly distributed between octahedral and tetrahedral sites in the interlayer space is stable. The changes in the crystal structure independent of temperature are in agreement with the previously proposed model, according to which the stability of the layered or the rhombohedral phase is determined by the entropy factor associated with the distribution of the intercalated atoms between the octahedral and tetrahedral sites in the interlayer space.