Low‐temperature Raman spectroscopic studies in NaNbO₃

Abstract

Raman spectroscopic measurements were carried out in the temperature range 10-300 K to understand the low-temperature antiferroelectric (AFE)-ferroelectric (FE) phase transition in NaNbO 3 . Several modes in the low wavenumber range were found to disappear, while some new modes appeared across the transition. The temperature dependence of mode wavenumbers suggests that, during cooling, the AFE-FE phase transition begins to occur at 180 K, while the reverse transition starts at 260 K during heating. During cooling, the two phases were found to coexist in the temperature range of 220-160 K. Upon heating, the FE phase is retained up to 240 K and both FE and AFE phases coexist in the temperature range 240-300 K. In contrast to the earlier reports, the present results suggest a different coexistence region and the reverse transition temperature. The reported relaxor-type FE behaviour over a broad temperature is consistent with the observed coexistence of phases during cooling and heating cycles.

Dielectric and polarized Raman spectroscopic studies on 0.85Pb(Zn1/3Nb2/3)O3-0.15PbTiO3 single crystal

“…6(b)) geometries show a discontinuous change at $473 K. It may be mentioned that the mode disappearance, mode broadening, and discontinuous change in mode frequencies are typical for Perovskite ferroelectrics undergoing a phase transition. 18,25 Therefore, the present observations suggests that the system undergoes a tetragonal to cubic phase transition at $473 K, which is close to the transition temperature reported from XRD measurement 16 as well as the dielectric results discussed earlier. Figures 4(b) and 5(b) show the Raman spectra in high temperature cubic phase.…”

“…10,[17][18][19] Phonon anomalies induced by temperature changes are associated with phase transitions. [17][18][19][20][21] Furthermore, it has the advantage that light couples directly with the ferroelectric order parameter (polarization) and is therefore useful in study of PNRs dynamics also.…”

“…10,[17][18][19] Phonon anomalies induced by temperature changes are associated with phase transitions. [17][18][19][20][21] Furthermore, it has the advantage that light couples directly with the ferroelectric order parameter (polarization) and is therefore useful in study of PNRs dynamics also. 11,12,[22][23][24] Raman spectroscopic studies have been reported for x ¼ 4.5%, 9 which is on the rhombohedral side of the phase diagram and also for x ¼ 8%, 25 the tetragonal side of phase diagram has not been reported across tetragonal-cubic phase transition.…”

High pressure Raman spectroscopic studies of the relaxor ferroelectric 0.85Pb(Zn1/3Nb2/3)O3-0.15PbTiO3

“…It can be mentioned that mode disappearance, discontinuous change in mode frequencies and appearance of new modes are typical signatures of a phase transition in a perovskite ferroelectric. 16,20,12,40 Thus the present system shows pressure induced instabilities around 2.2, 6.3 and 14.6 GPa, and these pressures are close to the transition pressures reported for PZN-PT with x = 0, 12 0.04, 39 and 0.1. 25 As mentioned in introduction, upon cooling below T B , the correlation among the PNRs increases; the PNRs coalesce to form large PNRs and subsequently develop into a long-range order normal ferroelectric at or above room temperature.…”

“…Many investigations such as neutron scattering, dielectric spectroscopy, Raman, Brillouin and infrared spectroscopy have been employed to understand the dynamical aspects of PNRs and their influence on macroscopic properties such as ferroelectric phase transition. 10,11,[14][15][16][17][18][19] Upon cooling, the dynamics of PNRs are described by three characteristic temperatures. At Burns temperature T B , the nucleation of PNRs begins, which is far above the temperature of dielectric permittivity maximum T m .…”