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ABSTRACT
The crystal structure and vibration spectra of sodium niobate NaNbO3 have been studied by means of neutron diffraction, X-ray diffraction and Raman spectroscopy at high pressures. An isostructural phase transformation from the initial antiferroelectric phase to an intermediate antiferroelectric phase HP-I have been observed under 2 GPa. This transformation is caused by complex reorientations of NbO6 octahedra. Subsequent structural phase transition from the phase HP-I to an orthorhombic phase HP-III have been detected at pressures above 10 GPa. This transition leads to suppression of an antiferroelectric state of NaNbO3. The observed phase transitions are accompanied by anomalies in lattice parameters compression.
Funding
The work has been supported by the RFBR grant №14–02-00948-a and by the Vietnam National Foundation for Science and Technology Development (NAFEOSTED) under grant number 103.02–2014.11. Portions of this research were carried out at the light source PETRA-III at DESY, a member of the Helmholtz Association (HGF). Financial support from the BMBF, Germany (Projects No 05K10RFA and 05K13RF1) is gratefully acknowledged. I.P.R. acknowledges support from the Ministry of Education and Science of Russian Federation through research projects 2132 and 3.1649.2017.