Synthesis and study of high-temperature heat capacity of erbium orthovanadate

Orthovanadate ErVO₄ has been prepared by solid-phase synthesis from a stoichiometric mixture of high pure V₂O₅ and chemically pure Er₂O₃ by multistage calcination in air in the temperature range 873–1273 K. The effect of temperature (380–1000 K) on the heat capacity of orthovanadate ErVO₄ was studied by hightemperature calorimetry. Thermodynamic properties of erbium orthovanadate (enthalpy change H°(T)–H°(380 K), entropy change S°(T)–S°(380 K), and reduced Gibbs energy Φ°(T)) have been calculated from the experimental C_p = f(T) data. It has been shown that the specific heat varies in a row of oxides and orthovanadates of Gd-Lu naturally depending on the radius of the R³⁺ ion within the third and fourth tetrads.     

Low temperature heat capacity of Nd2Zr2O7 pyrochlore

Heat capacity of neodymium zirconate (Nd₂Zr₂O₇) with pyrochlore structure was measured by adiabatic calorimetry and the hybrid adiabatic relaxation method in the temperature range (0.45 to 400) K. Its excess component was obtained by comparison with the heat capacity of the lanthanum zirconate. A thermal anomaly was observed below T=7.2 K. From the heat capacity measurements, the thermodynamic functions of Nd₂Zr₂O₇ were determined.     

High-temperature heat capacity of YbAl3(BO3)4

The isobaric heat capacity C _p (T) of YbAl₃(BO₃)₄ grown by spontaneous crystallization from solution (100 ? n) wt % (Bi₂Mo₃O₁₂ + 2.5% B₂O₃ + 0.75% Li₂MoO₄) + n wt % YbAl₃(BO₃)₄ is studied experimentally in the region of 344–1016 K. It is established that there are no extrema on the C _p (T) dependence, and the obtained data can be described using the Berman-Brown polynomial. The temperature variations of enthalpy and entropy are calculated from the C _p (T) dependence.     

High-temperature heat capacity of zirconolite (CaZrTi2O7)

Enthalpy increment measurements in the range of (520 to 1570) K were carried out utilizing drop calorimetry on zirconolite (CaZrTi₂O₇). The high-temperature dependence of the heat capacity of zirconolite has been determined from the simultaneous analysis of our enthalpy increment measurements and published low-temperature heat capacity data.     

Structural and spectroscopic study of a novel erbium titanate pink pigment prepared by sol-gel methodology

Pyrochlore oxides show a large variety of physical and chemical properties depending on the ordering/disordering of the cations and oxygen vacancies. Taking account of these structural features and the luminescent properties of lanthanides, a new family of colored materials is investigated. This paper studies the structural evolution of the erbium titanate system with temperature to establish its influence on the color properties. The success on the development of color is completely related to the sol-gel preparation method, underlining its higher reactivity compared to classical solid-state synthesis. After firing at 700 degrees C, the sol-gel material develops an intense pink coloration whose intensity significantly diminishes at 800 degrees C. X-ray diffraction and Rietveld refinements indicated the presence of nanocrystals with a fluorite-like structure at 700 degrees C, responsible for the intense coloration, which suffers a gradual atomic rearrangement toward an "ideal" pyrochlore phase. These results were corroborated by infrared and Raman measurements. UV-vis spectroscopy showed the influence of the Er(3+)-O bond covalence on the spectral properties. This study opens new perspectives to the development of more ecological colored sol-gel materials based on rare earth elements. Furthermore, the combination of the optical aspects with the classical pyrochlore properties (magnetization, heat capacity, conductivity, etc.) would provide new multifunctional materials for advanced applications.     

Synthesis and properties of chromium-containing bismuth titanates with the pyrochlore structure

Chromium-containing bismuth titanates with the pyrochlore-type structure Bi_1.6Cr _x Ti₂O_6.4+1.5x were synthesized by the ceramic method. The region of formation of solid solutions of pyrochlores (chromium-doped bismuth titanates) was determined. The picnometric and X-ray densities were compared, and the electrophysical and magnetic characteristics were studied.     

Fitting of heat capacity peaks of PCMs with a theoretical formula

Journal of Thermal Analysis and Calorimetry - We introduce an explicit theoretical formula for the heat capacity peaks that occur in materials during phase changes. Such materials are of importance...     

Cluster structure of water in accordance with the data on dielectric permittivity and heat capacity

In the work the character of water clusterization in the whole existence domain of its liquid state is discussed: from supercooled states to the critical point. Conclusions about the cluster composition of liquid water are drawn based on the analysis: 1) of the features of dielectric relaxation; 2) character of the temperature dependence of its static dielectric permittivity, and 3) the value and temperature dependence of different contributions to the heat capacity of the system. It is shown that near the water crystallization point tetramers prevail in its structure, with an increase in the temperature trimers start to play the main role, and near the critical point of water dimers become the major associates. At temperatures near the water crystallization point the obtained results well agree with the data on emission and absorption X-ray spectroscopy.     

Synthesis and properties of Sc- and Mg-doped bismuth titanates with the pyrochlore structure

Scandium(Magnesium)-containing bismuth titanates with the pyrochlore structure have been synthesized for the first time. Their homogeneity range has been determined by means of X-ray diffraction analysis and scanning electronic microscopy. Scandium and magnesium distribution over the cationic positions has been studied. Electrophysical properties of single-phase compounds have been studied. The total conductivity of the compounds is a function of magnesium (scandium) and bismuth concentrations.     

Hydrogen titanate nanofibers covered with anatase nanocrystals: a delicate structure achieved by the wet chemistry reaction of the titanate nanofibers

Hydrogen titanate nanofibers synthesized by a hydrothermal reaction, are chemically reactive, readily reacting with dilute acid. This reaction is a topochemical process in which in situ phase transition from H-titanate to anatase takes place and the product retains the fibril morphology. The extent of this reaction can be precisely controlled, allowing us to achieve a delicate composite structure at nanoscale: long titanate fibers of 40-100 nm thick and up to 30 mum long covered with anatase nanocrystals of 10-30 nm. The structure has desired photocatalytic properties and can be separated readily after use. This study demonstrates new opportunities to create delicate inorganic nanostructures with advanced functions by wet chemical reactions.     

Synthesis of novel cation-ordered compounds with fluorite-related structure prepared by oxidation of Sn-Ta-O pyrochlore

Pyrochlore-type oxide, Sn^II_1.64(Ta_1.88Sn^IV_0.12)O_6.58 was oxidized for exploring novel metastable phases. Two novel Sn^IV_0.82(Ta_0.94Sn^IV_0.06)O_4.11 phases with a fluorite-related structure, which was obtained as a pure phase, and with a rutile-related structure appearing as an impurity for the fluorite-related phase were successfully obtained similar to the previous Sn-Nb-O system. The ordered arrangement of respective cations of Sn and (0.94Ta+0.06Sn) in the precursor Sn^II_1.64(Ta_1.88Sn^IV_0.12)O_6.58 was left in the both oxidized Sn^IV_0.82(Ta_0.94Sn^IV_0.06)O_4.11 phases. In contrast to the previous Sn-Nb-O system, the cation-ordered α-PbO₂-related Sn^IV_0.82(Ta_0.94Sn^IV_0.06)O_4.11 could not be obtained in the present conditions. Such a difference between the Sn-Ta-O and Sn-Nb-O systems was interpreted by larger energy barrier of the transformation from the fluorite-related phase to α-PbO₂-related phase in Sn-Ta-O system than in Sn-Nb-O system.     

On the defect structure of calcium titanate with nonideal cationic ratio

The defect structure of polycrystalline calcium titanate with Ca/Ti = 0.998, 0.995, and 0.992 was investigated by measuring the equilibrium electrical conductivity as a function of oxygen partial pressure (P_O2 = 10⁰–10^?20 atm) at 950–1050°C. These data were similar to that obtained in the sample with ideal cationic ratio. The deviation from ideal Ca-to-Ti ratio is found to be accommodated by the formation of neutral vacancy pairs, (V″_CaV^··₀). The results indicate that the single-phase field of calcium titanate extends beyond 50.201 mole% TiO₂.     

Study of temperature profile and specific heat capacity in temperature modulated DSC with a low sample heat diffusivity

One important application of temperature modulated DSC (TMDSC) is the measurement of specific heat of materials. When the sample has very good thermal conductivity as in the case of metals, the temperature gradient is not normally an important factor and can be ignored most of the time. However, in the case of materials with poor heat transfer properties, for example, polymers, the thermal conductivity is only in the order of 1/1000 or so of that of metals. This could have a major effect on the test results. In this paper, a round analytical solution is given and a numerical model is used to analyze the effects of thermal diffusivity on temperature distribution inside the test sample and specific heat measurement by TMDSC, PET sample test results are presented to demonstrate the effects of material thermal diffusivity.     

The heat capacity of polymers

The long path to an understanding of heat capacity is traced from isothermal and adiabatic calorimetries to the most recent three methods of isoperibol, scanning, and temperature-modulated calorimetry (TMDSC). These latter three methods are: the traditional method of scanning thermal analysis; the quasi-isothermal method of finding the maximum amplitude of the periodic heat flow in response to a temperature modulation at a constant base temperature; and the pseudo-isothermal analysis of a temperature-modulated scanning experiment by subtracting the effect due to the underlying constant heating rate. In parallel, the development of the knowledge about phases and molecules is traced from its beginning to present-day nanophases and macromolecules.     

Low-temperature heat capacity of diglycylglycine

Heat capacity of tripeptide diglycylglycine was measured in a temperature range from 6.5 to 304 K. The results were compared with those for glycine and glycylglycine. Peptide bonding was found not to change C _P(T) virtually above 70 K, where heat capacity does not obey the Debye model. Comparison with literature data allows one to expect a significant difference in the heat capacity for enantiomorph and racemic species of valine and leucine, like it was found recently for D-and DL-serine.     

The structure of diluted binary solutions of amides according to the heat capacity data

The specific heat capacities of hexamethylphosphoric triamide, diethylpropionamide, their aqueous solutions, and mixtures of hexamethylphosphoric triamide with formamide were measured in the temperature range from 288.15 to 318.15 K. The dependences of the partial molar heat capacity of aqueous solutions of amides on the composition of the mixture have maxima in the region of 0.02–0.04 molar fractions of amide. The maximum on a similar dependence for solutions of hexamethylphosphoric triamide corresponds to the concentration of 0.01 molar fractions. The conclusion on the formation of solvates (hydrates) in the systems studied was made. The heat capacity coefficients of pair and triple interactions were calculated in terms of the McMillan-Mayer theory. A change in the heat capacity characteristics with the temperature change was analyzed. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2479–2483, December, 1998.