Landau theory and giant room-temperature barocaloric effect
Corrales Salazar, A.
Brierley, Richard T.
Littlewood, Peter B.
Guzmán Verri, Gian Giacomo
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The structural phase transitions of MF3 (M = Al, Cr, V, Fe, Ti, Sc) metal trifluorides are studied within a simple Landau theory consisting of tilts of rigid MF6 octahedra associated with soft antiferrodistortive optic modes that are coupled to long-wavelength strain generating acoustic phonons. We calculate the temperature and pressure dependence of several quantities such as the spontaneous distortions, volume expansion, and shear strains as well as T−P phase diagrams. By contrasting our model to experiments we quantify the deviations from mean-field behavior and find that the tilt fluctuations of the MF6 octahedra increase with metal cation size. We apply our model to predict giant barocaloric effects in Sc-substituted TiF3 of up to about 15JK−1kg−1 for modest hydrostatic compressions of 0.2GPa. The effect extends over a wide temperature range of over 140K (including room temperature) due to a large predicted rate, dTc/dP=723KGPa−1, which exceeds those of typical barocaloric materials. Our results suggest that open lattice frameworks such as the trifluorides are an attractive platform to search for giant barocaloric effects.
External link to the item10.1103/PhysRevMaterials.1.053601
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