L V Kirensky Institute of Physics, Siberian Division, Russian Academy of Sciences, Akademgorodok, Krasnoyarsk, 660036, Russia.
J Phys Condens Matter. 2010 May 12;22(18):185901. doi: 10.1088/0953-8984/22/18/185901. Epub 2010 Apr 15.
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.
对 (NH(4))(2)NbOF(5) 晶体沿 a、b 和 c 轴的热膨胀进行了测量，温度范围为 120 至 300 K。在 T(1) = 259.3 K 和 T(2) = 220.5 K 时，所有方向上都观察到了与先前报道的 Cmc2(1) --> C2 --> 1a 相转变相关的 α(T)异常。在 Pippard 关系框架内对热膨胀和热容的分析使我们能够确定转变温度 dT/dσ(i)的单轴压力导数。T-σ(i)相图表明，在 b 和 c 轴方向上高应力下中间相有消失的趋势。在结构相变附近发现了强的和广延的压热效应，其热参数可与某些铁电体、铁磁体和反铁磁体的热参数相媲美。
