Barocaloric effect near the structural phase transition in the Rb2KTiOF5 oxyfluoride

Conventional and inverse barocaloric effects around triple points in ferroelastics (NH 4 ) 3 NbOF 6 and (NH 4 ) 3 TiOF 5

“…Both extensive and intensive BCE in oxyfluorides were determined by the previously used method [15] using the data on heat capacity, [11,12] the T − p phase diagrams and temperature and pressure dependences of the phase transition entropies obtained in the present paper. Taking into account the negligible effect of low pressure (p ≤ 0.5 GPa) on ∆S i (Fig.…”

Disorder and phase transitions in oxyfluoride (NH4)3Ta(O2)2F4

“…were determined on the ground of approach used by us in [4,11]. Total entropy S(T,p) of compounds undergoing phase transitions is the sum of the lattice S lat and anomalous DS contributions.…”

“…The composition of crystals was refined in accordance with the peroxo (O 2 ) 2À group content determined by the permanganatometry titrimetric method. The results revealed the 2 mass.% deficiency of (O 2 ) 2À groups relative to stoichiometric composition (NH 4 Structural characterization of (NH 4 ) 3 Ta(O 2 ) 2 F 4 was performed using X-ray powder diffractometry. The unit-cell constant has been refined at room temperature in the cubic space group: a 0 = 0.9435(5) nm, and found to be in rather good agreement with the parameters determined in previous structural investigations -0.9414(7) nm [12], 0.94512(4) nm [13].…”

Thermal, dielectric and barocaloric properties of NH4HSO4 crystallized from an aqueous solution and the melt

“…Of course the fall of δS 2 as well as δV 2 under pressure is not common peculiarity of phase transitions. For example, recent studies of the T -p phase diagrams in some perovskite-like ferroelastics have shown the constancy of the entropy jump at phase transition point at least in the range of p = 0 -0.5 GPa [25,26].…”

“…We were also not able to determine the ΔS 2 * (T, p) dependence for NH 4 HSO 4 . However, taking into account that the maximum value of the extensive BCE ΔS BCE max near T 2 is equal to the phase transition entropy ΔS 2 , one can perform raw estimation of the minimum pressure, p min , which produces the maximum values of ΔS BCE max as well as ΔT AD max [26] p dp…”