Search Results

You are looking at 1 - 5 of 5 items for

  • Author or Editor: D. Sedmidubský x
  • Refine by Access: All Content x
Clear All Modify Search

Abstract  

An effort for a better understanding of the phase formation and their stability in the ternary system Bi2O3−SrO−CuO led to investigations of the phase equilibria, particularly in the sub-solidus region. To extend this phase region about the respective solid-liquid equilibria the isothermal and pseudobinary cuts of the BiO1.5−SrO−CuO ternary system in the temperature range from 810 to 850°C were determined. A particular attention was also devoted to the thermodynamic stability of the Bi2+xSr2−yCuO6+δ phase.

Restricted access

Thermochemical and thermodynamical properties of HTSC phases are reviewed for the Y-Ba-Cu-O system and also presented for the newly calculated Bi-Sr-Cu-O system stressing out stoichiometric and phenomenological viewpoints. Simulated data are listed for (H 298 o-H o o, phase transformation temperatures, standard entropies, standard enthalpies of formation, heat capacities in crystalline phase, etc. Pseudobinary phase diagrams are treated showing the effect of oxygen partial pressure particularly illustrated on the (Sr, Bi, Ba)-Cu-O system.

Restricted access

Abstract  

Heat capacity and enthalpy increments of calcium niobates CaNb2O6 and Ca2Nb2O7 were measured by the relaxation time method (2–300 K), DSC (260–360 K) and drop calorimetry (669–1421 K). Temperature dependencies of the molar heat capacity in the form C pm=200.4+0.03432T−3.450·106/T 2 J K−1 mol−1 for CaNb2O6 and C pm=257.2+0.03621T−4.435·106/T 2 J K−1 mol−1 for Ca2Nb2O7 were derived by the least-squares method from the experimental data. The molar entropies at 298.15 K, S m 0(CaNb2O6, 298.15 K)=167.3±0.9 J K−1 mol−1 and S m 0(Ca2Nb2O7, 298.15 K)=212.4±1.2 J K−1 mol−1, were evaluated from the low temperature heat capacity measurements. Standard enthalpies of formation at 298.15 K were derived using published values of Gibbs energy of formation and presented heat capacity and entropy data: Δf H 0(CaNb2O6, 298.15 K)= −2664.52 kJ molt-1 and Δf H 0(Ca2Nb2O7, 298.15 K)= −3346.91 kJ mol−1.

Restricted access

Heat capacity and phonon spectra of A IIIN

Experiment and calculation

Journal of Thermal Analysis and Calorimetry
Authors:
D. Sedmidubský
,
J. Leitner
,
P. Svoboda
,
Z. Sofer
, and
J. Macháček

Abstract  

The low temperature heat capacities of three A IIInitrides, A III=Al, Ga and In, were measured by relaxation method in the temperature range 2–300 K and the corresponding entropies at the reference temperature 298.15 K were evaluated from the experimental data. The lattice heat capacity at constant volume was also assessed theoretically within harmonic crystal approximation by direct method using a combination of VASP software package to obtain the Hellmann-Feynman forces and the Phonon program to calculate the phonon spectra. The experimental data were analyzed by means of a Debye-Einstein model taking use of the calculated heat capacity and involving additionally an anharmonic contribution.

Restricted access
Journal of Thermal Analysis and Calorimetry
Authors:
J. Leitner
,
M. Hampl
,
K. Růžička
,
M. Straka
,
D. Sedmidubský
, and
P. Svoboda

Abstract  

The heat capacity and the enthalpy increments of strontium metaniobate SrNb2O6 were measured by the relaxation method (2-276 K), micro DSC calorimetry (260-320 K) and drop calorimetry (723-1472 K). Temperature dependence of the molar heat capacity in the form C pm=(200.47±5.51)+(0.02937±0.0760)T-(3.4728±0.3115)·106/T 2 J K−1 mol−1 (298-1500 K) was derived by the least-squares method from the experimental data. Furthermore, the standard molar entropy at 298.15 K S m 0 (298.15 K)=173.88±0.39 J K−1 mol−1 was evaluated from the low temperature heat capacity measurements. The standard enthalpy of formation Δf H 0 (298.15 K)=-2826.78 kJ mol−1 was derived from total energies obtained by full potential LAPW electronic structure calculations within density functional theory.

Restricted access