Dielectric dispersion of the relaxor PLZT ceramics in the frequency range 20 Hz-100 THz

Abstract

The dielectric dispersion of the transparent relaxor ferroelectric ceramics PLZT 8/65/35 and 9.5/65/35 was determined in a wide frequency range including the microwave and infrared range. The number of observed polar phonons in infrared spectra gives evidence about the locally broken cubic symmetry and the presence of polar nanoclusters in the whole investigated temperature range up to 530 K. A single broad and symmetric dispersion that occurs below the polar phonon frequencies was fitted with the Cole-Cole formula and a uniform distribution of Debye relaxations. On decreasing temperature, the distribution of relaxation times becomes extremely broad which indicates increasing correlation among the clusters. The mean relaxation time diverges according to the Vogel-Fulcher law with the same freezing temperature 230±5 K for both ceramics, but different activation energies 1370 K and 1040 K for the 8/65/35 and 9.5/65/35 sample, respectively. The shortest relaxation time is about 10-12 s and remains almost temperature independent. Below room temperature, the loss spectra become essentially frequency independent and the permittivity increases linearly with decreasing logarithm of frequency. The slope of this dependence is proportional to T 4 in the investigated temperature range (above 210 K) which indicates appreciable anharmonicity of the potential for polarization fluctuations.

Structure and dielectric dispersion in cubic-like 0.5K 0.5 Na 0.5 NbO 3 -0.5Na 1/2 Bi 1/2 TiO 3 ceramic

“…A frequency-dependent broad maxima with frequency dispersion is discerned in both ε' and ε" for the KNN-50BNT ceramic. The profiles of the frequency dispersion are very similar to PLZT 8/65/35 relaxors that are of cubic symmetry at room temperature 21 , but different from 0.94BNT-0.06BaTiO3 ceramics in which strong frequency dispersion appears in the temperature range before the maximum of ε (T'm) 22 . The relaxation behavior is not caused by space charge polarization or ion hopping because the complex permittivity does not follow the Cole-Cole equation 23 , as shown in Fig.…”

Soft and central mode behaviour in PbMg1/3Nb2/3O3relaxor ferroelectric

“…It can be fitted by a uniform distribution of relaxation frequencies, much broader than the experimental frequency window. 37 We suggest that this is due to the influence of random fields on the distribution of activation energies for breathing of polar clusters. 5 We measured also the in-plane dielectric response of PMN thin film on sapphire between 10 kHz and 1 MHz.…”

Frequency and temperature dependent transport properties of NiCuZn ceramic oxide

“…It is also observed from the plots that the higher dielectric loss occurs at higher temperature and lower frequencies. This is understandable from the fact that at lower frequencies the trend is due to space charge polarization and at higher temperatures the trend may be due to macroscopic distortion of charges [30].…”