Landau theory and giant room-temperature barocaloric effect in MF${}_3$ metal trifluorides

Abstract

The structural phase transitions of MF${}_3$ (M=Al, Cr, V, Fe, Ti, Sc) metal trifluorides are studied within a simple Landau theory consisting of tilts of rigid MF${}_6$ octahedra associated with soft antiferrodistoritive 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 found that the tilt fluctuations of the MF${}_6$ octahedra increase with metal cation size. We apply our model to predict giant barocaloric effects in Sc substituted TiF${}_3$ of up to about $15$JK${}^{-1}$kg${}^{-1}$ for modest hydrostatic compressions of $0.2$GPa. The effect extends over a wide temperature range of over $140$K (including room temperature) due to a large predicted rate $d{T}_c/dP=723$K GPa${}^{-1}$, 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.

arXiv comment11 pages, 8 figures

References in corpus (7)

• Barocaloric and Magnetocaloric Effects in Fe49Rh51
• Anomalous thermal conductivity and suppression of negative thermal expansion in ScF3
• First-principles re-investigation of bulk WO3
• Large isotropic negative thermal expansion above a structural quantum phase transition
• The role of static disorder in negative thermal expansion in ReO3
• Density Functional Study of Cubic to Rhombohedral Transition in $\alpha$-AlF${}_3$
• Octahedral Tilt Instability of ReO_3-type Crystals

Cited by in corpus (3)

• Colossal pressure-induced softening in scandium fluoride
• Negative thermal expansion near the precipice of structural stability in open perovskites
• Landau Theory of Barocaloric Plastic Crystals