Effect of Deuteration on the Thermodynamic Properties of Dioxotetrafluoromolybdate(VI), (NH 4 ) 2 MoO 2 F 4

Thermal and dielectric studies of (ND ) MoO F crystals undergoing successive phase transitions at T = 272 K and T = 181 K showed that deuteration is accompanied by an increase in the chemical pressure in the crystal lattice (Δp ≈ 0.02 GPa), which shifts the Cmcm ↔ Pnma transformation for the first o...

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Bibliographic Details
Published in:Inorganic chemistry 2017-06, Vol.56 (11), p.6706-6711
Main Authors: Bogdanov, Evgeniy V, Pogoreltsev, Evgeniy I, Gorev, Mikhail V, Flerov, Igor N
Format: Article
Language:English
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Summary:Thermal and dielectric studies of (ND ) MoO F crystals undergoing successive phase transitions at T = 272 K and T = 181 K showed that deuteration is accompanied by an increase in the chemical pressure in the crystal lattice (Δp ≈ 0.02 GPa), which shifts the Cmcm ↔ Pnma transformation for the first order to the tricritical point. The direct participation of ammonium groups in the mechanism of structural distortions is demonstrated by a decrease in the entropy of the high-temperature phase transition (ΔS = R ln 6.0). An external hydrostatic pressure leads to an expansion of the temperature interval of the intermediate antiferroelectric Pnma phase. The triple point on the T-p phase diagram, where the Cmcm, Pnma, amd Pnma* phases coexist, can be realized at a negative pressure of p ≈ -0.8 GPa.
ISSN:0020-1669
1520-510X
DOI:10.1021/acs.inorgchem.7b00811