Suppression of antiferroelectric state in NaNbO3 at high pressure from in situ neutron diffraction

Abstract

We report direct experimental evidence of antiferroelectric to paraelectric phase transition under pressure in NaNbO 3 using neutron diffraction at room temperature. The paraelectric phase is found to stabilize above 8 GPa and its crystal structure has been determined in orthorhombic symmetry with space group Pbnm.The variation of the structural parameters of the both orthorhombic phases as a function of pressure was determined. We have not found evidence for structural phase transition around 2 GPa as previously suggested in the literature based on Raman scattering experiments, however, significant change in Nb-O-Nb bond angles are found around this pressure. The response of the lattice parameters to pressure is strongly anisotropic with a largest contraction along <100>. The structural phase transition around ~ 8 GPa is followed by an anomalous increase in the orthorhombic strain and tilt angle associated with the R point (q= ½ ½ ½). Ab-initio calculation of the enthalpy in the various phases of NaNbO 3 is able to predict the phase transition pressure well.

Probing of structural phase transitions in barium titanate modified sodium niobate using Raman scattering

“…On lowering the temperature, it undergoes transition to a series of antiferrodistortive phases in this order: tetragonal (T2) P4/mbm, orthorhombic (T1) Cmcm, orthorhombic (S) Pbnm, orthorhombic (R) Pbnm, orthorhombic (P) Pbcm phases, and a rhombohedral R3c phase . Pressure‐induced phase transition from room temperature antiferroelectric orthorhombic ( P bcm ) phase to paraelectric orthorhombic ( P bnm ) phase is also reported in literature . These structural phase transitions involve phonon mode instabilities linked with zone centre and zone boundary phonon modes with respect to the cubic phase .…”

Monoclinic ferroelectric NaNbO3 at room temperature: Crystal structure solved by using super high resolution neutron powder diffraction

“…In the present study the Na-deficiency is considered to play an important role in forming Table 1 Summary of the Rietveld refinement results for the TOF neutron data for the candidate models. Both the powder sample obtained by pulverizing the sintered pellet at 1573 K (upper part) (1) and the pellet sample (lower part) (2) were analyzed.…”

“…Pulverized pellet (1) Pcmb ( a R-factors with weighted profile pattern (R wp ), pattern (R p ), Bragg factor (R b ), structure factor (R f ), and goodness-of-fit (χ2¼ R wp /R e ) 2 (R e : expected-R). the two phases.…”

“…Although NaNbO 3 has been studied for several decades, both the crystal structure and electric properties are not completely understood [1][2][3]. This material has attracted considerable interest because it provides not only a matrix phase for various lead-free piezoelectric materials, such as (Ag, Na, K)NbO 3 [4] and (Li, Na)(Nb, Ta)O 3 [5], but also has potential applications in piezoelectric nanodevices [6].…”

Evidence of low‐temperature phase transition in BaTiO3‐modified NaNbO3: Raman spectroscopy study

“…It is found that the antiferroelectric phase transforms to the ferroelectric phase (space group: Pmc2 1 ) on small substation of Na + ion by Li + . These structural phase transitions involve cationic displacement and tilting of the oxygen octahedra and have been characterized by various techniques such as X‐ray and neutron diffraction and Raman spectroscopy …”