Thermal expansion, phase diagrams and barocaloric effects in (NH4)2NbOF5
- 15 April 2010
- journal article
- Published by IOP Publishing in Journal of Physics: Condensed Matter
- Vol. 22 (18), 185901
- https://doi.org/10.1088/0953-8984/22/18/185901
Abstract
The thermal expansion along the a, b and c axes of a (NH(4))(2)NbOF(5) crystal was measured from 120 to 300 K. Anomalies of α(T) associated with previously reported phase transitions Cmc2(1) --> C2 --> 1a were observed along all directions at T(1) = 259.3 K and T(2) = 220.5 K. The analysis of thermal expansion and heat capacity in the frame of the Pippard relations has permitted us to determine the uniaxial pressure derivatives of the transition temperatures dT/dσ(i). The T-σ(i) phase diagrams have shown a tendency for the intermediate phase to disappear at high stress along the b and c axes. Intensive and extensive barocaloric effects near the structural phase transitions were found to be comparable with the caloric parameters of some ferroelectrics, ferromagnets and antiferromagnets.Keywords
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