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Vapour pressure and mixing thermodynamic properties of the KNbO3–NaNbO3system

Popovič, A. and Bencze, L. and Koruza, Jurij and Malič, Barbara (2015):
Vapour pressure and mixing thermodynamic properties of the KNbO3–NaNbO3system.
5, In: RSC Adv., (93), pp. 76249-76256. ISSN 2046-2069,
[Article]

Abstract

Equilibrium vapour pressures of sodium and potassium over a KxNa1−xNbO3 solid solution within its whole compositional range at temperatures between 1173 K and 1303 K were determined by Knudsen Effusion Mass Spectrometry. It should be noted that the thermodynamic equilibrium between the condensed and the vapour phase could be established only after prolonged annealing (more than 10 h at 1263 K). The equilibrium vapour pressure of potassium over K0.5Na0.5NbO3 (KNN) is a few times larger than that of sodium, i.e., 8 × 10−3 Pa as compared to 3 × 10−3 Pa at 1263 K. From the obtained results, the excess thermodynamic functions for the pseudo-binary KNbO3–NaNbO3 system were evaluated. The excess Gibbs energy was found to be positive, the excess enthalpy is close to zero, while the negative excess entropy indicates a partial ordering of alkaline ions in the solid solution. The comparison of the obtained results to the well-established lead-based piezoelectric systems revealed, that the vapour pressure of alkalis over the respective niobates at 1200 K is almost three orders of magnitude lower as compared to the values reported for lead oxide over Pb(Zr,Ti)O3.

Item Type: Article
Erschienen: 2015
Creators: Popovič, A. and Bencze, L. and Koruza, Jurij and Malič, Barbara
Title: Vapour pressure and mixing thermodynamic properties of the KNbO3–NaNbO3system
Language: English
Abstract:

Equilibrium vapour pressures of sodium and potassium over a KxNa1−xNbO3 solid solution within its whole compositional range at temperatures between 1173 K and 1303 K were determined by Knudsen Effusion Mass Spectrometry. It should be noted that the thermodynamic equilibrium between the condensed and the vapour phase could be established only after prolonged annealing (more than 10 h at 1263 K). The equilibrium vapour pressure of potassium over K0.5Na0.5NbO3 (KNN) is a few times larger than that of sodium, i.e., 8 × 10−3 Pa as compared to 3 × 10−3 Pa at 1263 K. From the obtained results, the excess thermodynamic functions for the pseudo-binary KNbO3–NaNbO3 system were evaluated. The excess Gibbs energy was found to be positive, the excess enthalpy is close to zero, while the negative excess entropy indicates a partial ordering of alkaline ions in the solid solution. The comparison of the obtained results to the well-established lead-based piezoelectric systems revealed, that the vapour pressure of alkalis over the respective niobates at 1200 K is almost three orders of magnitude lower as compared to the values reported for lead oxide over Pb(Zr,Ti)O3.

Journal or Publication Title: RSC Adv.
Volume: 5
Number: 93
Divisions: 11 Department of Materials and Earth Sciences > Material Science > Nonmetallic-Inorganic Materials
11 Department of Materials and Earth Sciences > Material Science
11 Department of Materials and Earth Sciences
Date Deposited: 14 Sep 2015 12:59
Official URL: http://dx.doi.org/10.1039/c5ra11874c
Identification Number: doi:10.1039/c5ra11874c
Funders: This work was nancially supported by the Slovenian Research Agency (1000-08-310121; P2-0105; J2-1227)
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