Effect of deuteration on the barocaloric properties of complex vanadates (NH4)3VO F6− (x: 1, 2)

We report on the analysis of intensive and extensive barocaloric properties and their sensitivity to deuteration of complex oxyfluorides (NH 4 ) 3 VO x F 6− x (x: 1, 2) undergoing a similar sequence of structural phase transitions. Due to the high sensitivity to hydrostatic pressure and the strong disordering of six-coordinated anionic fluoro-oxygen species, (NH 4 ) 3 VO 2 F 4 and (ND 4 ) 3 VO 2 F 4 crystals demonstrate the highest barocaloric efficiency at low pressure, p = 0.1 GPa, during the phase transition from the initial cubic phase: barocaloric coefficients reach large values |Δ S BCE |/ p ≈ 400 J/(kg K GPa) and Δ T AD / p ≈ 80 K/GPa. Anionic, [VOF 5 ] → [VO 2 F 4 ], and cationic, [ND 4 ] → [NH 4 ] substitutions are accompanied by a decrease in the disorder of structural units in the cubic phase, which leads to a decrease in changes in entropy and temperature under pressure. The contribution of thermal expansion of the crystal lattice to the total intensive and extensive barocaloric effects is large and amounts to about 30–40%. • Deuteration reduces structural disorder in (NH 4 ) 3 VO x F 6-x (x: 1,2) oxyfluorides. • Effect of chemical pressure on phase transitions due to substitution of V 4+ .→V 5+ • Highest barocaloric efficiency of (NH 4 ) 3 VO 2 F 4 at low pressure, p = 0.1 GPa. • Significant contribution of the crystal lattice to the total barocaloric effect.