Heat capacity and thermodynamic properties of LiGaO2 from 180 to 700 K

The heat capacity at constant pressure of LiGaO₂ is measured in the temperature range from 180 to 700 K. An analysis of the experimental data shows that the anharmonic contribution to the heat capacity can be described by a polynomial of fourth order in the temperature. The standard enthalpies and entropies relative to 298.15 K are calculated from the measured heat capacity. Estimates of the standard enthalpy and entropy at 298.15 K are given.     

Heat capacity and lattice anharmonicity in CdBIVC chalcopyrite compounds

The heat capacity at constant pressure of CdSiP₂, CdGeP₂, CdSnP₂ and CdGeAs₂ is measured in the temperature range from 300 to 500 K. The anharmonic contribution to the heat capacity is evaluated and it is shown that the degree of lattice anharmonicity decreases with increasing atomic weight of the constituent atoms of the compounds. Comparing the temperature variation of the heat capacity and of the thermal expansion coefficient some conclusions are made regarding the interatomic potential in the A^IIB^IVC compounds.     

Heat capacity of LiInS2, LiInSe2 and LiInTe2 between 200 and 550 K

The molar heat capacity at constant pressure of LiInS₂, LiInSe₂ and LiInTe₂ was measured in the temperature range from about 200 K to 550 K. An analysis of the experimental data showed that the anharmonic contribution to the heat capacity can be described by a polynomial of fourth order in the temperature. A comparison of the results for the LiInC₂^VI compounds with those for the AgB^IIIC₂^VI and A^IIB^IVC₂^V chalcopyrite compounds showed that the lattice anharmonicity effects are essentially influenced by the specific nature of the Li C^VI bond.     

Heat capacity of Ag6Ge10p12 from 180 to 550 K

The molar heat capacity at constant pressure of Ag₆Ge₁₀P₁₂ is measured in the temperature range from 180 to 550 K and the standard molar enthalpies and entropies relative to 298.15 K are calculated on the basis of these data. From a comparison of the temperature variation of the apparent Debye temperatures in CuGe₂P₃ and Ag₆Ge₁₀P₁₂ it is concluded that lattice anharmonicity is more pronounced in Ag₆Ge₁₀P₁₂ than in CuGe₂P₃.     

Experimental evidence against the existence of an ideal glass transition

The absolute liquid heat capacity of poly(α-methyl styrene) was determined at temperatures far below T_g and T_K in previous work by use of pentamer/polymer athermal mixtures. Here the data is compared to data compiled by Wunderlich and coworkers from 0 K to above T_g in order to obtain the absolute entropy for the polymer in its equilibrium state at temperatures as much as 180 K below the glass temperature or 130 K below the Kauzmann temperature. The results provide no evidence of a second-order transition or of a smeared transition in the entropy. In addition, we find no evidence that the entropy would become negative at a finite temperature.     

The specific heat capacities of V2O5/P2O5-based glasses

The specific heat capacities of a series of V₂O₅/P₂O₅-based glasses have been measured in the approximate temperature range 3–300 K. The proportions of the host constituents were varied and the effects produced by adding oxides of copper, titanium and sodium were examined. The measurements were extended to investigate the influence of fast neutron irradiation upon the specific heat capacity of pure, initially crystalline V₂O₅.The observations are consistent with a spectrum of background vibrations, the form of which is temperature dependent. At intermediate temperatures the vibrations were consistent with the glasses displaying predominantly chain-like characteristics. With reduction to lower temperatures the vibrational behaviour increasingly resembled that of solids displaying three-dimensional characteristics. The temperature dependence of the specific heat capacity at the lowest temperatures was consistent with the presence of a narrow band of low-frequency modes centred upon 1.67 × 10¹¹ s^?1, the density of which increased with phosphorus content. From observations of the density of these modes in the doped specimens, it was concluded that the role of copper wass largely that of a network former, whereas titanium and sodium were essentially network modifiers.     

The Heat Capacity of 1,2,4,5-Tetracyanobenzene and of its 1 : 1 Charge-Transfer Complex with Pyrene from 10 K to 300 K

Abstract

The heat capacity of 1,2,4,5-tetracyanobenzene and of its 1 : 1 complex with pyrene has been measured form ～ 10 K to ～ 300 K. There is a transition in the complex which appears as an approximately symmetrical anomaly in the heat capacity-temperature curve between ～ 220 K and 250 K, but the heat capacity is not reproducible in this region even if the sample is subjected to the same preliminary thermal treatment. Moreover, the room-temperature form can be undercooled at least down to 150 K. In the two runs in which the heat capacity anomaly was most prominent. C_p reached its maximum at 232 ± 1 K. The largest measured value of the entropy of transition was 9.2 JK^?1 mol^?1. This value is compatible with but does not prove, the exisstence of static disorder above the transition, with one of the components (pyrene, in the light of the structural information) having at least two distinguishable orientations. At all temperatures in the range covered (apart from the transition region), the heat capacity of the complex is less than the sum of that of the pure components, and possible reasons for this are brifly discussed.     

High-temperature specific heat of AgInS2 and AgGaSe2

The molar specific heat at constant pressure was measured for AgInS₂ and AgGaSe₂ in the temperature range from 300 to 500 K. An analysis of the experimental data showed that the contribution to the specific heat due to lattice anharmonicity can be described by a polynomial of third order in the temperature. This result is in agreement with the temperature dependence of the specific heat expected from thermal expansion data.     

Specific Heat and Lattice Anharmonicity in ZnSiP2 and ZnSiAs2

The molar specific heat at constant pressure was measured for ZnSiP₂ in the temperature range from 300 to 400 K and for ZnSiAs₂ from 300 to 500 K. An analysis of the experimental data showed that the contribution to the specific heat due to lattice anharmonicity can be described by a polynomial of third order in the temperature. Predictions are made regarding the expected temperature dependence of the thermal expansion coefficients and compared with existing experimental data.     

Sound velocity in alumino-silicate liquids determined up to 2550 K from Brillouin spectroscopy: glass transition and crossover temperatures

Hypersonic longitudinal sound velocities in five silicate and alumino-silicate liquids have been measured between 293 and 2550 K by Brillouin spectroscopy. Together with previous observations for four other glasses and liquids of the system SiO₂-Al₂O₃-CaO-MgO, these results are used to discuss changes in hypersonic velocities in three adjacent temperature domains, i.e., below, in, and above the glass transformation range. The temperature dependence of Brillouin velocities is consistent with the observed variations with temperature of viscosity, density, and mean heat capacity for the same three temperature domains. These variations of physical properties of alumino-silicate liquids are qualitatively in agreement with the Inherent Structure Theory for liquids.     

Non-Debye excess heat capacity and boson peak of binary lithium borate glasses

The non-Debye excess heat capacities of binary lithium borate glasses with different Li₂O compositions of x = 8, 14 and 22 (mol%) are investigated to understand origin of the boson peak. The low-temperature heat capacities are measured between 2 and 50 K by a relaxation calorimeter. The experimental non-Debye heat capacities with x = 14 is successfully reproduced using the excess vibrational density of states measured by inelastic neutron scattering. This finding indicates that the non-Debye heat capacities of lithium borate glasses originate from the excess vibrational density of states measureable by inelastic neutron scattering. Moreover, it is demonstrated that all of the excess heat capacity spectra lie on a single master curve by the scaling using boson peak temperature and intensity.     

Heat capacities and thermal behavior of alkali borate glasses

The heat capacities of selected glasses in the five alkali borate systems have been measured over a range of high temperatures which includes the respective glass transition regions. The heat capacities per gram atom at 350°K show little variation with composition while those at the low temperature ends of the glass transition, T_g-, show some systematic variations. When compared with the respective 3R values, the heat capacities at T_g- range from about 0.75 for B₂O₃ to values in excess of unity for various alkali borate compositions. The present data on heat capacity have been combined with previous data on the elastic moduli, densities and thermal expansion coefficients to evaluate the Grüneisen constant, γ, for each composition for temperatures around ambient. For B₂O₃, γ has a low value of about 0.25. It decreases with additions of Li₂O and increases with additions of the other alkali oxides.     

Heat Capacity and Thermodynamic Properties of p'-Substituted p-n-Hexyloxybenzylideneaniline. I. p-n-Hexyloxybenzylideneamno-p'-Benzonitrile (HBAB)

Abstract

The heat capacity of the nematogenic liquid crystal, HBAB, has been measured between 15 K and 385 K by using an adiabatic calorimeter. The crystal-crystal phase transition has been discovered at 27 K below the crystal-nematic phase transition temperature. The transition temperatures, the enthalpies and the entropies of the three phase transitions have been determined: T ₁ = 306.98 K, ΔH _t = 5.11 kJ mol^?1, ΔS _t = 16.7 JK^?l; T _m = 334.05 K, ΔH _m = 23.77 kJ mol^?1, ΔS_m = 71.2 J K^?l mol^?1; and T _c = 375.10 K, ΔH _c = 1.75 kJ mol^?1, ΔS _c = 3.2 J K^?1 mol^?1, respectively. The thermodynamic functions of HBAB from 0 K to 385 K have been determined from the heat capacity data and the enthalpies of the transitions. Two crystal modifications, one yellow and granular form and the other white and needle-like form, have been obtained during the course of the preparation of the sample. It turned out that the yellow form was the stable crystal and the white the metastable modification. The crystal-crystal phase transition has been discussed as an onset of partial melting from the entropy consideration. In this connection the total entropies of the transitions, 91.1 J K^?1 mol^?1 has been proposed to be an important measure of melting.     

Thermodynamics of formation of aluminum-iron-germanium amorphous alloys

Thermodynamic properties of ternary liquid Al-Fe-Ge alloys were studied by electromotive force method at 1050-1250 K and by high-temperature isobasic calorimetry at 1740 ± 5 K. The heat capacity change at ternary alloy formation (Δ_mixC_p) was estimated using the temperature dependence of integral enthalpy of mixing. Thermodynamics of the formation of Al-Fe-Ge amorphous alloys was evaluated by extrapolation of thermodynamic functions of mixing to the temperature of amorphization. The process of glass forming is preferable by both enthalpy and entropy for compositions of (0.1<x_Fe<0.6, x_Ge<0.5). The area with most negative integral Gibbs free energy and enthalpy of amorphous alloy formation corresponds well to the area of amorphization estimated by a glass-forming tendency (GFT) criterion.     

Thermal and EPR investigations of thallium gallium disulphide single crystal

In this research, the results of the differential scanning calorimetry (DSC) and electron paramagnetic resonance (EPR) investigations of TlGaS₂ single crystal are presented. Specific heat capacity (C_p) anomalies of layered TlGaS₂ have been obtained by using a new DSC technique for such crystals. Remarkable heat capacity anomalies have been revealed at the temperatures of 137.7 K, 174.5 K and 238.5 K. It is found that the anomalies appear at maximum with a small deviation (by 3‐4%) from the regular values, and C_p discontinuity amounted to approximately 5%. Additionally, EPR spectra of Fe doped TlGaS₂ single crystals have been recorded at various temperatures down to 6 K for different orientations of the applied magnetic field. Transformations of present EPR spectra are not sufficient for the confirmation of structural phase transitions, in contrast to the cases in iso structural TlInS₂ and TlGaSe₂ compounds. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Ultrasound propagation in glasses in the metastable immiscibility region of the sodium borosilicate system

Measurements of ultrasound wave velocity and attenuation have been made between 1.3 K and 400 K in a series of both quenched and heat-treated Na₂OB₂O₃SiO₂ glasses. As in many other inorganic glasses, the ultrasound attenuation of both longitudinal and shear waves below room temperature is dominated by a broad and intense loss peak; the height and temperature of the peak maximum are frequency sensitive. The loss peak characteristics are consistent with a structural relaxation mechanism with a distribution of activation energies and this model is used to analyse the data. The features of the acoustic loss peak and also the absolute value and temperature coefficient of ultrasound velocity are strongly dependent on the total Na₂O network modifier content of the glasses. The ultrasound wave propagation is also affected by phase-separation inducing heat treatment: a steady rise in the height of the acoustic loss peak and an upward shift in the peak temperature takes place with increasing time of heat treatment at 550°C, a finding which suggests that structural rearrangements are still occurring in the individual glassy phases even after long periods of heat treatment. It is proposed that heat treatment causes migration of Na⁺ ions away from BOB bonds in the B₂O₃ rich phase.     

Thermal properties of a Nd:LuVO4 crystal

A Nd‐doped lutetium orthovanadate Nd:LuVO₄ crystal has been grown using a modified Czochralski method. The thermal properties of this crystal have been studied by measuring the thermal expansion, specific heat and thermal diffusivity. The thermal expansion coefficients are α₁₁ = 1.7 × 10^‐6, α₂₂ = 1.5 × 10^‐6 and α₃₃ = 9.1 × 10^‐6/K in the temperature range of 298–573 K along the three respective crystallographic axes. The specific heat is almost linear and increases from 0.442 to 0.498 Jg^‐1K^‐1 in the measured temperature range. The thermal diffusivity is anisotropic and decreases with increasing temperature from 295 to 548 K. At room temperature the calculated thermal conductivities κ₁₁ and κ₃₃ are 7.96 and 9.77 Wm^‐1K^‐1, respectively. These thermal parameters of Nd:LuVO₄ crystal have indicated that it is an excellent candidate laser material. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Anomalous heat capacity of vitreous silica: Effect of interstitial 4He

⁴He (gas or liquid) sorbs into SiO₂ glass at liquid helium temperatures. The term in the heat capacity of vitreous silica which is linear in temperature is increased by the presence of interstitial ⁴He. (The linear term is believed to be generally characteristic of glasses). A number of experiments on SiO₂ glass are suggested using H₂, ³He, and ⁴He as probes of mass 2, 3, and 4 to explore the mechanism which is responsible for the anomalous heat capacity.     

A thermodynamic and kinetic investigation of amorphous (1−x)As2Se3 · xSb2Se3 alloys

The heats of formation of amorphous (1?x)As₂Se₃ · xSb₂Se₃ (x = 0 to 0.4) referred to crystalline As₂Se₃ and Sb₂Se₃ were measured by liquid metal solution calorimetry. The values of heats of formation of amorphous (1?x)As₂Se₃ · xSb₂Se₃ decreased from 1.39 ± 0.03 kcal · (g-at)^?1 at x = 0 to 1.27 ± 0.04 kcal · (g-at)^?1 at x = 0.4.The glass transition temperature and the temperatures of the maximum rates of crystallization and fusion were measured by differential scanning calorimetry. The glass transition temperature increased and the temperatures of the maximum rates of crystallization and fusion decreased with increasing Sb₂Se₃ content.The relaxation process in amorphous (1?x)As₂Se₃ · xSb₂Se (x = 0.3) was investigated by measuring changes in microhardness, small-angle X-ray scattering and heat capacity with time of annealing at several temperatures ranging from room temperature to 413 K. With increasing annealing time the microhardness, the height and the temperature of the glass transition peak increased whereas the intensity of small-angle X-ray scattering decreased. These changes reflect relaxation towards a more stable structure of smaller molecular mobility. The changes in the enthalpy with annealing time and the activation energy spectra for relaxation were derived from the heat capacity data. The effects of temperature and time of annealing on the various properties are explained in terms of structural changes and relaxation kinetics.