High-Temperature Evolution of the Incommensurate Composite Crystal Ca_0.83CuO₂

• Main Authors: Lara Righi, Marco Merlini, Mauro Gemmi
• Format: Article
• Language: English
• Published: MDPI AG 2020-07-01
• Series: Crystals
• Subjects: composite crystals; Ca-based cuprates; incommensurate modulation; powder synchrotron diffraction study.
• Online Access: https://www.mdpi.com/2073-4352/10/7/630
• ISSN: 2073-4352

The crystal structure of the composite crystal Ca_0.83CuO₂ was investigated by synchrotron powder diffraction at high temperature. The incommensurate modulated structure was firstly analyzed at room temperature (RT) and successfully solved by adopting the (3D + 1)-dimensional symmetry P2₁/m(α0γ)0s. The composite crystal is featured by a non-uniform distribution of Ca ions occupying octahedral sites formed by the spatial arrangement by the infinite 1D CuO₂ chains. By approaching 500 K, Ca_0.83CuO₂ undergoes a structural rearrangement ruled by the shrinking of the Ca interatomic distances. The high-temperature crystalline phase is characterized by a different incommensurate periodicity requiring the recombination of the Ca/CuO₂ balance featuring the composite intergrowth of the two almost independent sub-structures. We ascertain that the new crystalline form is stable up to 950 K near to the limit of the thermal decomposition.