Thermal, structural, optical, dielectric and barocaloric properties at ferroelastic phase transition in trigonal (NH4)2SnF6: A new look at the old compound

Flerov, I. N.; Карташев, А. В.; Горев, М. В.; Bogdanov, E. V.; Melnikova, S. V.; Molokeev, Maxim S.; Pogorel’tsev, E. I.; Laptash, N. M.

doi:10.1016/j.jfluchem.2015.12.010

Cited by 31 publications

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“…Our largest reversible value of |Δ S | ≈ 30 J K −1 kg −1 arose at T ≈ 285 K using |Δ p | ≈ 1.7 kbar [Figure c], which compares favorably with other BC materials that are magnetic (Table S1, Supporting Information). Our volume‐normalized value of |Δ S | ≈ 0.25 J K −1 cm −3 also compares well with other BC solids (Table S1, Supporting Information) [we identify a density of 8000 kg m −3 from the measured lattice parameters in Figure b and Figure S1b, Supporting Information]. Importantly, the large pressure‐induced shift of transition temperatures [Figure b] permits large entropy changes to be driven over a wide range of temperatures.…”

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confidence: 81%

“…A similar shift of the anhysteretic transition temperature d T 0 /d p ≈ −10 K kbar −1 was obtained by applying the Clausius–Clapeyron equation d T 0 /d p = Δ V 0 /Δ S 0 in the limit of atmospheric pressure p atm ≈ 0 kbar, with a specific volume change of Δ V 0 ≈ −5 mm 3 g −1 [Figure b] and Δ S 0 ≈ 47 J K −1 kg −1 [Figure d]. These shifts are amongst the largest observed for any BC material, and would permit the full transition of width T h2 – T h1 ≈ 13 K to be fully driven in either direction using |Δ p | = | p − p atm | ≈ | p | ≈ 1.3 kbar. Integration of (d Q /|d T |)/ T at finite pressure reveals that |Δ S 0 | undergoes a significant decrease with increasing pressure (at roughly −6.5 J K −1 kg −1 kbar −1 ) [Figure c], implying via the Clausius–Clapeyron equation a pressure‐induced suppression of |Δ V 0 | [Figure d].…”

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confidence: 68%

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Giant and Reversible Inverse Barocaloric Effects near Room Temperature in Ferromagnetic MnCoGeB_0.03

et al. 2019

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phase transitions, [17][18][19][20][21][22][23] and it is straightforward to exploit a fragmented BC working body by encapsulating it together with the pressure-transmitting medium. Here we use variable-pressure calorimetry to investigate giant BC effects in the well-known [24,25] MC material MnCoGeB 0.03 near the ≈290 K paramagnetic/hexagonal to ferromagnetic/orthorhombic phase transition (PM/H to FM/O). This transition is associated with a giant change of volume (≈4%) that causes this brittle material to undergo a complete mechanical failure that would be problematic in MC cooling devices. [26] Moderate changes of pressure (|Δp| ≈ 1.7 kbar) drive giant and reversible MC effects of |ΔS| ≈ 30 J K −1 kg −1 and |ΔT| ≈ 10 K. These BC effects are similar to the MC effects that would require impractically large changes of magnetic field (µ 0 ΔH ≈ 10 T) in order to be reversible (µ 0 is the permeability of free space). Our study shows that hydrostatic pressure represents an inexpensive and practical method of driving caloric effects in brittle MC materials. More generally, our study incorporates MnCoGebased compounds into the growing family of multicaloric materials. [27] Above the magnetostructural transition temperature of T 0 ≈ 290 K, MnCoGeB 0.03 adopts the PM/H phase (P63/mmc or Ni 2 In-type space group). [24] On cooling the sample through Hydrostatic pressure represents an inexpensive and practical method of driving caloric effects in brittle magnetocaloric materials, which display first-order magnetostructural phase transitions whose large latent heats are traditionally accessed using applied magnetic fields. Here, moderate changes of hydrostatic pressure are used to drive giant and reversible inverse barocaloric effects near room temperature in the notoriously brittle magnetocaloric material MnCoGeB 0.03 . The barocaloric effects compare favorably with those observed in barocaloric materials that are magnetic. The inevitable fragmentation provides a large surface for heat exchange with pressure-transmitting media, permitting good access to barocaloric effects in cooling devices.

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confidence: 81%

supporting

confidence: 68%

Giant and Reversible Inverse Barocaloric Effects near Room Temperature in Ferromagnetic MnCoGeB_0.03

et al. 2019

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“…Recently, studies of differential thermal analysis under pressure for some complex fluorides and oxyfluorides revealed the absence of the pressure effect, at least to 0.6 GPa, on the phase transition entropy [14][15][16]. Taking into account these results, we assumed that in the case of K 2 TaF 7 pressure also does not affect ∆S.…”

Section: Barocaloric Effectmentioning

confidence: 93%

Heat capacity, thermal expansion and barocaloric effect in fluoride $$\hbox {K}_{2}\hbox {TaF}_{7}$$

et al. 2019

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Heat capacity and thermal dilatation of potassium heptafluorotantalate were studied. Room temperature phase P21/c is stable at least to 4 K. Strong first order phase transition P21/c ↔ Pnma at T0 = 486.2 K is accompanied by giant changes in the entropy, ΔS0 = 22.3 J/mol•K, and volume strain, δV0/V =-3.5%. A rather high sensitivity of K2TaF7 to pressure was found, dT0/dp =-220 K/GPa. Significant extensive and intensive barocaloric effects are found at low pressure. The possibility of improving the barocaloric properties is discussed.

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“…7 we compare our values for isothermal entropy change and adiabatic temperature change to those reported for state-of-the-art magnetic barocaloric has an excellent stability in their thermodynamic and structural properties 23 . In addition to magnetic alloys, giant barocaloric effects have also been reported in a broad variety of materials including ferroelectric [35][36][37] and ferrielectric 38 materials, fluorides 39,40 , hybrid perovskites 41 and superionic conductors 42 . Among all these materials only (NH 4 ) 2 NbOF 5 40 exhibits an isothermal entropy change (∆S = 100 J kg −1 K −1 ) larger than the value found for our Ni 50 Mn 31.5 Ti 18.5 shape memory Heusler alloy.…”

Section: Methodsmentioning

confidence: 99%

Giant barocaloric effect in all- d -metal Heusler shape memory alloys

Aznar

Gràcia-Condal

Planes

et al. 2019

Phys. Rev. Materials

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We have studied the barocaloric properties associated with the martensitic transition of a shape memory Heulser alloy Ni50Mn31.5Ti18.5 which is composed of all-d-metal elements. The composition of the sample has been tailored to avoid long range ferromagnetic order in both ausenite and martensite. The lack of ferromagnetism results in a weak magnetic contribution to the total entropy change thereby leading to a large transition entropy change. The combination of such a large entropy change and a relatively large volume change at the martensitic transition gives rise to giant barocaloric properties in this alloy. When compared to other shape memory Heusler alloys, our material exhibits values for adiabatic temperature and isothermal entropy changes significantly larger than values reported so far for this class of materials. Furthermore, our Ni50Mn31.5Ti18.5 also compares favourably to the best state-of-the-art magnetic barocaloric materials.

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Thermal, structural, optical, dielectric and barocaloric properties at ferroelastic phase transition in trigonal (NH4)2SnF6: A new look at the old compound

Cited by 31 publications

References 15 publications

Giant and Reversible Inverse Barocaloric Effects near Room Temperature in Ferromagnetic MnCoGeB_0.03

Giant and Reversible Inverse Barocaloric Effects near Room Temperature in Ferromagnetic MnCoGeB_0.03

Heat capacity, thermal expansion and barocaloric effect in fluoride $$\hbox {K}_{2}\hbox {TaF}_{7}$$

Giant barocaloric effect in all- d -metal Heusler shape memory alloys

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Thermal, structural, optical, dielectric and barocaloric properties at ferroelastic phase transition in trigonal (NH4)2SnF6: A new look at the old compound

Cited by 31 publications

References 15 publications

Giant and Reversible Inverse Barocaloric Effects near Room Temperature in Ferromagnetic MnCoGeB0.03

Giant and Reversible Inverse Barocaloric Effects near Room Temperature in Ferromagnetic MnCoGeB0.03

Heat capacity, thermal expansion and barocaloric effect in fluoride $$\hbox {K}_{2}\hbox {TaF}_{7}$$

Giant barocaloric effect in all- d -metal Heusler shape memory alloys

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Giant and Reversible Inverse Barocaloric Effects near Room Temperature in Ferromagnetic MnCoGeB_0.03

Giant and Reversible Inverse Barocaloric Effects near Room Temperature in Ferromagnetic MnCoGeB_0.03