Authors:
J. Leitner Institute of Chemical Technology Prague Department of Solid State Engineering Technická 5 166 28 Prague 6 Czech Republic

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K. Růžička Institute of Chemical Technology Prague Department of Physical Chemistry Technická 5 166 28 Prague 6 Czech Republic

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D. Sedmidubský Institute of Chemical Technology Prague Department of Inorganic Chemistry Technická 5 166 28 Prague 6 Czech Republic

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P. Svoboda Charles University Department of Condensed Matter Physics, Faculty of Mathematics and Physics Ke Karlovu 5 120 00 Prague 2 Czech Republic

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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 Cpm=200.4+0.03432T−3.450·106/T2 J K−1 mol−1 for CaNb2O6 and Cpm=257.2+0.03621T−4.435·106/T2 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, Sm0(CaNb2O6, 298.15 K)=167.3±0.9 J K−1 mol−1 and Sm0(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: ΔfH0(CaNb2O6, 298.15 K)= −2664.52 kJ molt-1 and ΔfH0(Ca2Nb2O7, 298.15 K)= −3346.91 kJ mol−1.

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Journal of Thermal Analysis and Calorimetry
Language English
Size A4
Year of
Foundation
1969
Volumes
per Year
1
Issues
per Year
24
Founder Akadémiai Kiadó
Founder's
Address
H-1117 Budapest, Hungary 1516 Budapest, PO Box 245.
Publisher Akadémiai Kiadó
Springer Nature Switzerland AG
Publisher's
Address
H-1117 Budapest, Hungary 1516 Budapest, PO Box 245.
CH-6330 Cham, Switzerland Gewerbestrasse 11.
Responsible
Publisher
Chief Executive Officer, Akadémiai Kiadó
ISSN 1388-6150 (Print)
ISSN 1588-2926 (Online)

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