The high-temperature phases of sodium niobate and the nature of transitions in pseudosymmetric structures

Abstract

The lattice parameters of NaNbO3 (which has a perovskite structure and is antiferroelectric at room temperature) have been measured by single-crystal X-ray methods from room temperature to 800°C. While the measurements are in substantial agreement with earlier work, the greater resolution shows up new details, and the interpretation of the earlier work has to be very seriously revised, particularly as concerns the symmetry of the high-temperature phases.Below the 360°C transition a second very similar phase Q can sometimes replace the normal roomtemperature phase P. Q is believed to be the 'forced ferroelectric' known to be produced from P by the action of an electric field; the field-free P-Q transitions are influenced by temperature but have not a reproducible transition temperature.Above 360°C there are a large number of transitions characterized by very different features. The facts from this and earlier work are critically reviewed. While the effects cannot yet be explained in detail, the general reasons for expecting such behaviour are discussed. No detailed structural work is reported, but there is evidence for the persistence of Nb displacements above 360 °C, which is therefore not the paraelectric transition.The transitions in a pseudosymmetric structure cannot be explained or predicted in terms of conventional or macroscopic theories which disregard structural details. A new empirical approach is needed, for which this system provides useful material.

Local structure of NaNbO3: A neutron scattering study

“…In particular Saito, et al 4 have designed a new lead-free ferroelectrics based on the MPB in the perovskite-rich region of (K,Na)NbO 3 , which shows excellent piezoelectric performance comparable to those of PZT. Interestingly their mother compound, sodium niobate, NaNbO 3 , is known for its complex phase behavior, and there are a number of conflicting reports on its structure [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22] . Thus there is a strong need for understanding the structure and phase transformation of sodium niobate.…”

Effects of doping and epitaxy on optical behavior of NaNbO3 films

“…[9][10][11] Bulk NNO possesses an orthorhombic crystal structure and exhibits an antiferroelectric behavior at room temperature. 12,13 When epitaxial NNO films are grown on top of cubic substrates, a monoclinic-type ferroelectric r-phase is expected to form in the films. 2 Here, such epitaxial Pr-doped and undoped NNO films are prepared.…”

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

“…Experimental studies of NaNbO 3 using a wide variety of techniques including x-ray and neutron diffraction [8][9][10][11][12][13][14][15] , Raman and infrared spectroscopy [16][17][18][19][20][21] , XAFS 22 , transmission electron microscopy (TEM) 23 , electron paramagnetic resonance (EPR) 24 , nuclear magnetic resonance (NMR) 25 , etc. have been reported and the crystal structure [8][9][10][11][12][13][14][15] , phonon spectrum [16][17][18][19][20][21]26 , dielectric and piezoelectric behavior 4,6,2 6-30 , temperature and pressure driven phase transitions and critical behavior of the order parameter 24,25 studied. First principles calculations of the structural and dynamical properties, epitaxial strain and anomalous LO-TO splittings of NaNbO 3 have also been reported.…”