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Temperature- and Pressure-Dependent Symmetry-Breaking Transitions in K2IrCl6
Caleb J Bennett1, Neha Bura2, Frederick P Marlton3
1School of Chemistry, The University of Sydney, Sydney, New South Wales 2006, Australia.
Inorganic Chemistry
|January 9, 2026
Summary
This study shows that K2IrCl6 exhibits local symmetry breaking at low temperatures, with distortions in its crystal structure. Pressure also induces transitions to lower-symmetry monoclinic phases, revealing complex structural behavior.
Area of Science:
- Materials Science
- Solid-State Chemistry
- Crystallography
Background:
- K2IrCl6 is a vacancy-ordered double perovskite with a cubic average crystal structure.
- Previous studies reported a stable cubic phase down to low temperatures.
- Understanding local structure and phase transitions is crucial for materials design.
Purpose of the Study:
- To investigate the local structure and symmetry of K2IrCl6 using variable temperature X-ray total scattering.
- To explore the structural response of K2IrCl6 to applied pressure using high-pressure synchrotron measurements.
- To elucidate the interplay between temperature, pressure, and structural phase transitions in K2IrCl6.
Main Methods:
- Variable temperature X-ray total scattering experiments.
- Pair distribution function (PDF) analysis.
- High-pressure synchrotron X-ray diffraction measurements.
Main Results:
- Evidence for local symmetry breaking in K2IrCl6, with anisotropic chloride displacements and octahedral distortions.
- Local structure is better described by a monoclinic P21/n model, indicating short-range distortions.
- Two reversible pressure-induced structural transitions observed: cubic to tetragonal at 12.0 GPa and tetragonal to monoclinic at 15.1 GPa.
- Significant increase in bulk modulus from 23 GPa to 121 GPa upon transition to the monoclinic phase.
Conclusions:
- Both temperature reduction and applied pressure drive K2IrCl6 towards lower-symmetry phases.
- This study provides direct local-structure evidence of symmetry breaking in K2IrCl6.
- Highlights the complex relationship between external stimuli and local structure in double perovskites.
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