Critical slowing down of polar nano regions ensemble in Gd3+-substituted PbMg1/3Nb2/3O3 ceramics

Abstract

Investigations on Gd-substituted lead magnesium niobate (Pb1-xGdxMg(1+x)/3Nb(2-x)/3O3; varying x = 0.01–0.1) ceramics have revealed critical slowing down of the polar nano regions (PNRs) ensemble into a “super-dipolar glass state” for higher Gd-substitution x ≥ 0.05. Low temperature electric field induced polarization switching study (P-E) has revealed a sharp decrease in the remanent polarization up to x = 0.03, which strengthen the critical slowing down of polar nano-domains dynamics, suggesting a reduction in the correlation between or within polar nano regions (PNRs) leading to a reduction in its size. Bright field imaging by using transmission electron microscope has also confirmed the reduction of the size of polar nano regions with increasing “x.” Selected area electron diffraction pattern along ⟨110⟩ unit axis has revealed enhancement in intensity of the superlattice reflections spot at ½ ½ ½ along ⟨111⟩ unit axis with increasing “x,” which is associated with the enhancement of chemical ordered regions and correlate well to enhancement in the degree of diffuseness parameters “δA” determined from fitting of the temperature dependent dielectric constant ε(T) plot above the dielectric maximum peak (εmax). The enhanced “δA” for x ≥ 0.05 is due to additional disorder created by the Gd-ions substitution at the Mg-site, which is consistent with the phase and microstructural analysis. Fitting of frequency dependent Tm (temperature of εmax) to the power law of critical dynamic has revealed realistic pre-factor fitting parameters for x ≥ 0.05 suggesting critical slowing down of the polar nano-domains dynamics ensemble resulting in super-dipolar glass state.

Role of charge compensation mechanism on phase formation, dielectric and ferroelectric properties in aliovalent Gd3+ ion modified PbMg1/3Nb2/3O3 ceramics

“…The ε m ~ 21762 and T m ~265 K for PMN are in good agreement with earlier reports [2,6,26]. The 4 at% Gd-ion substitution in PMN has reduced the T m (~ 30 K) and ε m (~7600) and is consistent with increase in size of the CORs, decrease in number or/and sizes of the PNRs and presence of the secondary pyrochlore and GdNbO 4 phases leading to reduction in correlation among the PNRs [26,33], which is also in good agreement with earlier reports on A-site substitution by alio-valent ions [37]. The least value of the ε m ~ 4360 is observed for PGMN4-VA compared to ~ 7600 for PGMN4-VB/R, which is due to presence of ~ 48% pyrochlore phase.…”

“…The charge imbalance due to powders. Details about the ceramic fabrication are similar to the earlier report [26,31]. In all the sintered ceramics, a sintered density greater than 97% of the theoretical is achieved.…”

“…The CORs and PNRs of PMN are correlated and reported to be influenced by application of an external electric field and/or A/B-site chemical substitution by alio-valent ions [19][20][21][22][23][24][25][26]. Application of an external electric field has revealed a phase transition from glass phase to ferroelectric phase at a critical field of ~2 kV/cm in the temperature range of 160 K -200 K [19].…”

Harmonic magneto-dielectric study in doped-, double-, and layered-perovskites

“…We obtain T g =211K, approach frequency f 0 =54 THz, and exponent z = 16. Here, we emphasize that a Vogel-Fulcher force-fit yields unphysical approach frequency f 0 , as also previously reported [9]; hence the VFT-model does not describe the dynamics of the system realistically.…”

“…fig. 5(e), it is clearly observed that the M''(f)relaxation peaks above 28K follow Arrhenic behaviour (T 0 =0K); with fitting parameters: f 0 =2.310 9 Hz and E a =29.2meV. Below T g =28K, relaxation peaks depict glassy behaviour with f 0 (approach frequency of dipoles) =1.110 7 Hz, E a =12.3meV, and T 0 =8K.…”