Details

Autor(en) / Beteiligte

• Flerov, Igor N.
• Kartashev, Andrey V.
• Gorev, Mikhail V.
• Bogdanov, Evgeniy V.
• Mel’nikova, Svetlana V.
• Molokeev, Maxim S.
• Pogoreltsev, Evgeniy I.
• Laptash, Natalia M.

Titel

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

Ist Teil von

• Journal of fluorine chemistry, 2016-03, Vol.183, p.1-9

Ort / Verlag

Elsevier B.V

Erscheinungsjahr

2016

Link zum Volltext

Quelle

Alma/SFX Local Collection

Beschreibungen/Notizen

• Comprehensive study of (NH4)2SnF6 revealed nonferroelectric first order transformation P-3m1↔P-1. Large entropy (∼Rln9) and volume (∼1%) change resulted from the order-disorder process at phase transition. A model of disordered NH4 tetrahedra in P-3m1 phase gives the entropy change close to the experimental value. Extensive and intensive barocaloric effects reached in (NH4)2SnF6 at low pressure ∼0.1GPa are comparable with those typical for known solid state coolants. [Display omitted] •Nonferroelectric first order phase transition P-3m1↔P-1found in (NH4)2SnF6.•A trigonal P-3m1 phase consists of disordered NH4 tetrahedra and ordered SnF6 octahedra.•Total structural ordering in P-1 phase leads to large entropy Rln9 and volume 1% change.•(NH4)2SnF6 is characterised by gigantic susceptibility to hydrostatic pressure with baric coefficient dT0/dp=−157K/GPa,•Large extensive and (61J/kgK) intensive (12K) barocaloric effects are realized at low pressure ∼0.1GPa. Structural phase transition P-3m1↔P-1 of the first order and nonferroelectric nature was found in (NH4)2SnF6 at about 110K in the process of thermal, optical, dielectric and X-ray studies. Order-disorder transformation is accompanied by large changes of entropy (ΔS0=16.4J/molK) and volume (ΔV0/V≈1%). The structural model associated with three orientations of NH4 tetrahedra in P-3m1 phase and their complete ordering in P-1 phase was suggested with the entropy change (ΔS0=18.3J/molK) close to the experimental value. A good agreement between baric coefficients measured in a direct way (dT0/dp=−157K/GPa) and evaluated using entropy and volume changes at phase transition (−170K/GPa) was found. Barocaloric effects in (NH4)2SnF6 are comparable with those of known solid state refrigerants and are characterised by a low-pressure need for realising their maximum values.