Characteristic behavior of the specific heat of exsolving 3He-4He solid solutions

Thermodynamics of dilute 3He–4He solid solutions with hcp structure

“…He and 4 He (others molecular impurities would be inevitable either separated or frozen during preparation of the solid helium samples). The thermodynamics of the helium mixed crystals with an arbitrary isotopic composition was studied experimentally [57][58][59] and interpreted theoretically [60][61][62] as the density-fluctuations phenomena over a self-consistent regular solid solution [63][64][65] under isotopic phase separation. In this connection the most pro- It should be noted that the closed system built of N atoms possesses exactly 3N translational degrees of freedom, and in a real crystal all the degrees are re-distributed among all excitations (phonons, impuritons, dislocations, etc.)…”

“…V C T in the 3 He- 4 He solid solutions is typical due to phase separation, and this phenomenon is studied in both experimental [57,59] and theoretical [61,62] aspects. The thermodynamic functions of the 3 He- 4 He mixed crystals demonstrate an anomalous behavior due to increasing in fluctuations near the equilibrium phase separation temperature, and this effect of density fluctuations in the impurity subsystem can be detected not only in the heat capacity [57,61,62] but also in the temperature-dependent phonon pressure within the preseparation region [71,72]. Moreover, as it follows from our previous results [53,61,62,71,72], the impurity contribution to the thermodynamic functions ( ) He appears over the lowtemperature anomalous peak which does not change neither its position nor magnitude with variation of 0 n in wide range of concentrations.…”

“…The thermodynamic functions of the 3 He- 4 He mixed crystals demonstrate an anomalous behavior due to increasing in fluctuations near the equilibrium phase separation temperature, and this effect of density fluctuations in the impurity subsystem can be detected not only in the heat capacity [57,61,62] but also in the temperature-dependent phonon pressure within the preseparation region [71,72]. Moreover, as it follows from our previous results [53,61,62,71,72], the impurity contribution to the thermodynamic functions ( ) He appears over the lowtemperature anomalous peak which does not change neither its position nor magnitude with variation of 0 n in wide range of concentrations. Nevertheless, this fact does not provide a way to conclude that the anomalous peak is absolutely independent on the presence of 3 He atoms in the 4 He matrix, because the impurities have a principal effect on the structural peculiarities and, hence, phonon spectrum of the hcp matrix, and give an effect to the phonon heat capacity within the whole temperature range (see Sec.…”