Heat Capacity Of Solid Solutions Research Articles

Phonon spectroscopy and features of low-temperature heat capacity of solid solutions of electrolytes

The kinetic characteristics of thermal frequency phonons in the region of helium temperatures in ceramic samples of the Ce1–xGdxO2–y electrolyte solid solution have been studied. To explain the temperature dependence of the phonon mean free path, we used the previously performed calculations of the energy of vacancy formation in the anion sublattice of a solid solution of zirconium dioxide stabilized by yttrium ZrO2:Y2O3 (YSZ) with a similar crystal structure. It is shown that in the Ce1–xGdxO2–y system under study, the formation of structural defects associated with the presence of vacancies in the anion sublattice with energy Δ = 8.53 K is possible. It has been established that analysis of the temperature dependences of the YSZ heat capacity allows one to trace the degree of disorder (amorphization) of the solid solution depending on its level of stabilization.

Oxidation and thermo physical studies of non-stoichiometric thorium uranium oxides prepared by gel combustion method

Thorium uranium oxide powder with uranium concentrations 10, 20, 30, 40, 50 and 70mol% was prepared by gel combustion method. The sintering behaviour of the powders studied by dilatometry indicated that samples containing uranium up to 30mol% had similar shrinkage behaviour with single step sintering. However, samples containing 40, 50 and 70% uranium followed two step sintering process. Though the air calcined powder shows two phase system beyond 30% uranium containing samples, sintering results into single phase system for samples containing up to 50% of uranium. The temperature programmed reduction-oxidation experiments showed that compositions containing up to 50-mol% of uranium show single reducible species throughout the temperature range. X-ray photoelectron spectroscopic studies of these sintered pellets showed presence of uranium in 6+ and 4+ oxidation states in these oxides. The experimentally determined heat capacities of solid solutions were found to have higher values than that of computed using Neumann–Kopp’s molar additivity rule.

リラクサー‐強誘電体固溶体PMN-PTおよびPZN-PTの熱容量と相転移挙動

リラクサー‐強誘電体固溶体PMN-PTおよびPZN-PTの熱容量と相転移挙動

Changes in the heat capacity of Al2O3-Cr2O3 solid solutions near the point of antiferromagnetic phase transition in Cr2O3

Al2O3-Cr2O3 solid solutions with 0, 4, 7, 10 and 20 mol% of corundum were synthesized using a high-pressure/high-temperature apparatus and characterized by X-ray powder diffraction. Calorimetric measurements were carried out using DSC-111 (Setaram). Heat capacity was measured by the enthalpy method in a temperature range of 260–340 K, near magnetic phase transition in pure Cr2O3 (305 K). Magnetic contribution into the heat capacity was derived and found to change irregularly with the composition. Heat capacity of solid solutions remains constant in a relatively wide range of composition, while the C p values of the end members differ significantly. This phenomenon is very important for the modeling of the thermodynamic functions of intermediate solid solutions.

Heat capacity of dilute solid solutions of diatomic molecules in the matrix of inert gases

A consistent theory is developed to describe temperature and concentration dependences of the excess impurity heat capacity of solid solutions of $^{14}\mathrm{N}_{2}$, $^{15}\mathrm{N}_{2}$, and ${\mathrm{O}}_{2}$ molecules in the matrix of inert gases Ar and Kr. It is shown that internal strain fields together with rotational degrees of freedom of the dissolving molecule contribute significantly to the thermodynamics of solutions already at concentrations about 0.1%. A comparison between obtained results and experimental data showed that the proposed theory is in good agreement with experiment up to the impurity concentrations of 1%.

Heat capacity of dilute solid solutions of diatomic molecules in the matrix of inert gases

A consistent theory is developed to describe temperature and concentration dependences of the excess impurity heat capacity of solid solutions of14N2,15N2, and O2 molecules in the matrix of inert gases Ar and Kr.

Heat capacity of solid solution of helium isotopes

The additional low-temeperature heat capacity of helium isotope solid solutions with a concentrationx3 of a few percent3He is calculated theoretically. The impurity contribution to the thermodynamics of the solution is assumed to be result of phase separation of the solid solution and the formation of quasi-one-dimensional structures of the second phase of3He atoms by their setting on lines of lattice dislocations or by the buildup of fractal structures. The excess heat capacity in the temperature interval 50–200 mK, is in the form of a peak, whose position essentially depends only on the depth of the potential well e0≃−1K created by a dislocation for an impurity atom. The height of the peak is determined primarily by the parameter ξ≏10−6−10−3, which represents the fraction of matrix lattice sites that can be occupied by the one-dimensional phase. The energy of interaction between impurities,U≏0.1K is found to have an insignificant influence on the shape and position of the peak. The theoretical results exhibit good agreement with published experimental data for a solution withx3=0.9%3He for one and only one choice of fitting parameters: ξ=0.0058;U=0.13K; e=−0.92K.

Impurity anomaly of heat capacity in solid parahydrogen and orthodeuterium

The heat capacity of solid solutions of neon in hydrogens with central intermolecular interaction (p-H2 and o-D2) is studied in the 0.8–8K temperature range. Temperature dependence of the neon impurities contribution (at concentrationsx≤0.25 mol. %) to heat capacity of such solutions passes its maximum at T=5.8 K. The magnitude of the effect does not depend on concentration of J=1 modifications of hydrogens (o-H2 and p-D2) and thus is determined by central intermolecular interaction only. In the case of solutions of Ne in p-H2, the impurity contribution per neon atom exceeds 9kB. An assumption is discussed that the very large impurity effects are due to the change of the location of hydrogen and deuterium molecules near heavy neon atoms at the temperature change.