3.6 Thermodynamic stability
Thermodynamic description of various potentials defines the possible
stability of these materials against high temperature and pressure. The
use of quasi-harmonic Debye model (QHM) [54] formulates the various
thermodynamic properties like Specific heat at constant volume
(Cv), Grüneisen parameter (γ) and thermal expansion
coefficient (α) in the temperature/pressure range of (0-800) K/ (0-25)
GPa. However, remaining under (QHM) model we have potrayed the Specific
performance of a material at constant volume (CV) which
is one of the prime factor of the material relating dynamics of the
material. Here, the graphical variation in Fig. 8 (a, b) , shows
that the materials possess greater capability of heat transport upon
T3 relation upto room temperature. The high
temperature limit suggests that change is accordance with the
Delong-Petit law with a constant value followed at high temperatures
[55].
Fig. 8 (a, b) : Variation of specific heat (Cv)
of RE2SnFeO6 (RE=Ca,Ba) with pressure and temperature.
Next, from the knowledge of the Grüneisen parameter (γ) labels the
anharmonicity and detailed description about the phonon frequency modes.
Fig. 8 (c, d) shows a softly increasing exponential trend at
the lower temperatures but remains almost constant at higher
temperatures. However the impact of pressure on (γ) has negligible
effect on it. The recorded value of Grüneisen parameter at temperature
300K and pressure 0 GPa are 2.20 and 2.25 respectively.
Fig. 8 (c, d) :Variation of Grüneisen parameter (γ) of
RE2SnFeO6 (RE=Ca,Ba) with pressure and temperature.
Thermal expansion (α) so for as theoretical as well as experimental
point of view predicts the thermodynamic equation of state. The
graphical representation w.r.t temperature and pressure variation for
layered alloys is shown in Fig. (e, f) . The fast increasing
trend of (α) at lower temperatures, while high temperature variation
tends towards constant value.
Fig. 8 (e, f) : Variation of thermal expansion (α) of
RE2SnFeO6 (Re=Ca,Ba) with pressure and temperature.