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Neutron diffraction studies using powder samples have been used to understandthe complex sequence of low temperature phase transitions of NaNbO3 in thetemperature range from 12 K-350 K. Detailed Rietveld analysis of thediffraction data reveal that the antiferroelectric to ferroelectric phasetransition occurs on cooling around 73 K while the reverse ferroelectric toantiferroelectric transition occurs on heating at 245 K. However, the formertransformation is not complete till down to 12 K and there is unambiguousevidence for the presence of the ferroelectric R3c phase coexisting with anantiferroelectic phase (Pbcm) over a wide range of temperatures. The coexistingphases and reported anomalous smearing of the dielectric response akin todipole glasses and relaxors observed in the same temperature range areconsistent with competing ferroelectric and antiferroelectric interactions inNaNbO3. We have carried out theoretical lattice dynamical calculations whichreveal that the free energies of the antiferroelectric Pbcm and ferroelectricR3c phases are nearly identical over a wide range of temperature. The smallenergy difference between the two phases is of interest as it explains theobserved coexistence of these phases over a wide range of temperature. Thecomputed double well depths and energy barriers from paraelectric Pm m toantiferroelectric Pbcm and ferroelectric R3c phases in NaNbO3 are also quitesimilar, although the ferroelectric R3c phase has a slightly lower energy.Comment: 15 pages, 6 Figs., 1 Tabl

physical review. b, condensed matter and materials physics

Competing antiferroelectric and ferroelectric interactions in<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mi mathvariant="normal">Na</mml:mi><mml:mi mathvariant="normal">Nb</mml:mi><mml:msub><mml:mi mathvariant="normal">O</mml:mi><mml:mn>3</mml:mn></mml:msub></mml:mrow></mml:math>: Neutron diffraction and theoretical studies

Competing antiferroelectric and ferroelectric interactions inNaNbO3: Neutron diffraction and theoretical studies