Low Temperature Physics: 46, 177 (2020); https://doi.org/10.1063/10.0000537
Fizika Nizkikh Temperatur: Volume 46, Number 2 (February 2020), p. 219-223 ( to contents , go back )
The effect of pressure on the negative thermal expansion of solid methane
Yu.A. Freiman and V.V. Vengerovsky
B. Verkin Institute for Low Temperature Physics and Engineering of the National Academy of Sciences of Ukraine 47 Nauky Ave., Kharkiv 61103, Ukraine
Geophysical Laboratory, Carnegie Institution of Washington 5251 Broad Branch Road NW, Washington D.C. 20015, USA
Received November 8, 2019, published online December 27, 2019
The effect of pressure on thermal expansion of solid CH4 is calculated for the low-temperature region where the contributions from phonons and librons can be neglected and only the rotational tunnelling modes are essential. The effect of pressure is shown to increase the magnitude of the peaks of the negative thermal expansion and shifts the positions of the peaks to the low-temperature region, which goes asymptotically to zero temperature with increasing pressure. The Grüneisen thermodynamical parameter for the rotational tunnelling modes is calculated. It is large, negative, and increases in magnitude with rising pressure.
Key words: solid methane, negative thermal expansion, Grüneisen thermodynamical parameter.