Structural studies of the P-T phase diagram of sodium niobate

Jabarov, S. G.; Kozlenko, D. P.; Kichanov, S. E.; Belushkin, A. V.; Mammadov, A. I.; Savenko, B. N.; Mekhtieva, R. Z.; Lathe, Christian

doi:10.1134/S1027451012060250

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Structural studies of the P-T phase diagram of sodium niobate

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Jabarov, S. G.
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Kozlenko, D. P.
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Kichanov, S. E.
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Belushkin, A. V.
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Mammadov, A. I.
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Savenko, B. N.
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Mekhtieva, R. Z.
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Lathe, Christian
CGS Centre for Geological Storage, Geoengineering Centres, GFZ Publication Database, Deutsches GeoForschungsZentrum;

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Jabarov, S. G., Kozlenko, D. P., Kichanov, S. E., Belushkin, A. V., Mammadov, A. I., Savenko, B. N., Mekhtieva, R. Z., Lathe, C. (2012): Structural studies of the P-T phase diagram of sodium niobate. - Journal of Surface Investigation: X-Ray Synchrotron and Neutron Techniques, 6, 3, 546-561.
https://doi.org/10.1134/S1027451012060250

https://gfzpublic.gfz-potsdam.de/pubman/item/item_245404

Abstract

The crystal structure of sodium niobate (NaNbO3) has been investigated by energy-dispersive X-ray diffraction at high pressures (up to 4.3 GPa) in the temperature range 300–1050 K. At normal conditions, NaNbO3 has an orthorhombic structure with Pbcm symmetry (antiferroelectric P phase). Upon heating, sodium niobate undergoes a series of consecutive transitions between structural modulated phases P-R-S-T(1)-T(2)-U; these transitions manifest themselves as anomalies in the temperature dependences of the positions and widths of diffraction peaks. Application of high pressure leads to a decrease in the temperatures of the structural transitions to the R, S, T(1), T(2), and U phases with different baric coefficients. A phase diagram for sodium niobate has been build in the pressure range 0–4.3 GPa and the temperature range 300–1050 K. The dependences of the unit-cell parameters and volume on pressure and temperature have been obtained. The bulk modulus and the volume coefficients of thermal expansion have been calculated for different structural modulated phases of sodium niobate. A phase transition (presumably, from the antiferroelectric orthorhombic P phase to the ferroelectric rhombohedral N phase) has been observed at high pressure (P = 1.6 GPa) and room temperature.