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Structural Phase Transitions and Magnetic Characterization of Ba2GdNbO6 for Low-Temperature Magnetocaloric
Fiamma Berardi1, Liam A V Nagle-Cocco1, James M A Steele2,1
1Cavendish Laboratory, University of Cambridge, JJ Thomson Avenue, Cambridge CB3 0US, U.K.
Chemistry of Materials : a Publication of the American Chemical Society
|November 17, 2025
Summary
This study reveals Ba2GdNbO6 exhibits tetragonal symmetry at room temperature, transitioning to monoclinic upon cooling and cubic upon heating. It shows promise for low-temperature magnetocaloric refrigeration due to its magnetic properties.
Area of Science:
- Materials Science
- Solid State Chemistry
- Crystallography
- Magnetism
Background:
- The crystal structure of Ba2GdNbO6 has been previously reported with varying symmetries (monoclinic, tetragonal, cubic) at room temperature.
- Understanding the precise structural phases and their transitions is crucial for exploring potential applications of double-perovskite materials.
Purpose of the Study:
- To precisely determine the room temperature crystal structure of Ba2GdNbO6.
- To investigate the temperature-dependent structural phase transitions of Ba2GdNbO6.
- To characterize the magnetic properties and magnetocaloric effect of Ba2GdNbO6 for potential applications.
Main Methods:
- High-resolution synchrotron X-ray diffraction.
- Neutron diffraction and neutron pair distribution function analysis.
- Magnetic susceptibility and heat capacity measurements.
Main Results:
- Ba2GdNbO6 adopts a tetragonal I4/m double-perovskite structure at room temperature with a subtle Jahn-Teller distortion.
- A phase transition to monoclinic P21/n symmetry occurs upon cooling to 2.4 K, and a reversible transition to cubic Fm-3m symmetry occurs upon heating to ~450 K.
- The compound exhibits paramagnetic behavior with weak ferromagnetic correlations and a maximum magnetic entropy change of -15.75 J K-1 mol-1 at 2 K and 9 T, indicating significant magnetocaloric potential.
Conclusions:
- Ba2GdNbO6 possesses distinct structural phases dependent on temperature, with a stable tetragonal phase at room temperature.
- The material demonstrates promising magnetocaloric properties, including a substantial magnetic entropy change and adiabatic temperature change.
- Ba2GdNbO6 is a strong candidate for low-temperature magnetocaloric refrigeration applications due to its effective cooling capability.
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