A multi-Debye relaxation model for relaxor ferroelectrics showing diffuse phase transition (original) (raw)
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Relaxor ferroelectric properties of PZT-PZN-PMnN Ceramics
2013
xPb(Zr 0.47 Ti 0.53)O 3-(0.925-x)Pb(Zn 1/3 Nb 2/3)O 3-0.075Pb(Mn 1/3 Nb 2/3)O 3 +0.7%wt Li 2 CO 3 (PZT-PZN-PMnN) ceramics with x=0.65-0.9 have been prepared by two-stage calcination method. The effect of the PZT content on the relaxor behavior and ferroelectric properties of ceramics has been investigated. The degree of diffuseness (γ) from 1.72 to 1.85 indicates that all of compositions show a diffused phase transition with the strong frequency dispersion, which is characteristic of relaxor ferroelectric materials. The sharpness of the permittivity peak shows that the compositions are gradually approached normal ferroelectric behavior when the mol fraction of PZT increases. At x = 0.80, dielectric and ferroelectric properties of ceramics are optimal with the mass density (ρ) of 7.81 g/cm3, the dielectric constant (εr) of 1230, the dielectric loss (tanδ) of 0.005 and the remanent polarization (Pr) of 27 µC/cm2.
Dielectric response of PLZT ceramics x/57/43 across ferroelectric–paraelectric phase transition
Bulletin of Materials Science, 2011
The dielectric properties of lead lanthanum zirconate titanate (PLZT) ceramics [Pb(Zr 0•57 Ti 0•43)O 3 + x at% of La, x = 3, 5, 6, 10 and 12] have been measured in the frequency range 1 Hz-1 MHz using the vector impedance spectroscopy (VIS) at different temperatures. All the compositions show both non-dispersive and dispersive dielectric responses in different temperature regions. The non-dispersive region obeys the universal dielectric response. A low frequency (<1 kHz) relaxation phenomenon with a high value of distribution parameter 'h' (∼0•4 to 0•6) has been observed in all the compositions around the temperature corresponding to the maximum dielectric constant (T m). The activation energies as calculated from the relaxation and d.c. conduction processes are comparable. The ferroelectric phase transition is diffuse in nature and broadening of the peak increases with La content.
Phase transition study in PLZT ferroelectric ceramics by mechanical and dielectric spectroscopies
Materials Science and Engineering: A, 2009
Measurements of anelastic and dielectric spectroscopies have been conducted in (Pb/La)(Zr/Ti)O 3 (PLZT) ferroelectric ceramics, with Zr/Ti = 65/35 and with La = 5 at.% and 8 at.%. Both the anelastic and the dielectric results have shown the presence of ferroelectric-paraelectric phase transitions around 250 • C for PLZT 5/65/35 and around 150 • C for PLZT 8/65/35, where the shift of the maximum elastic (electric) susceptibility for low temperatures with increase of lanthanum amount can be observed. The behavior of the relative variation of the elastic moduli as a function of the temperature was compared to the Landau-Devonshire theory of phase transitions. These results revealed the change of the kind of coupling between strain and order parameter in the ferroelectric-paraelectric phase transition with the increase of lanthanum concentration.
Applied Physics Letters, 2009
Tetragonal tungsten bronze-structured materials based on lead metaniobate ͑PbNb 2 O 6 ͒ were studied in terms of thermal dynamics of dielectric properties, showing ferroelectric-to-paraelectric phase transition of diffuse and relaxor type in some specific cases. These features are normally ascribed to defects-induced structural disorder and compositional fluctuations associated with an arbitrary lattice site occupation between dopant and host ions. Nevertheless, for these lead metaniobate-based materials, the drastic change in the phase transition from normal to diffuse and relaxor is shown to take place when dopants are able to significantly shift the transition toward low temperatures, where these compounds are known to exhibit incommensurate superstructures that naturally present diffuse and relaxor dielectric characteristics.
A Transition From Relaxor To Normal Ferroelectric: An Overview
International journal of engineering research and technology, 2013
Relaxors like PMN and PMN based materials proved to be promising candidate for multilayer capacitors (MLCs) and electrostriction actuators , pyroelectric bolometers, piezoelectric sensors replacing normal ferroelectrics such as BaTiO 3 and PZT. The compositional heterogeneity resulting from scale of ordering at the B-site influences relaxor to normal ferroelectric behavior .The genesis and growth of PMR resulted in ferroelectric transition. The distribution of curie points in PMR leads to DPT behavior. The dielectric relaxation is attributed to the relaxation of domain walls. Strong charge effects developed as a result of 1:1 ordering at the B-site limits the ordering of domains hence the size growth. The difference between NFE and RFE along with mechanism influencing the transition from RFE to NFE have been discussed.
Relaxor ferroelectric behavior of La substituted BPZT ceramics
Ceramics International, 2010
Barium titanate (BT) based compounds have been of great importance in the fabrication of multilayer ceramic capacitors. Several substitutions are used to tailor its structural, electrical and ferroelectric properties. Substituent like zirconium (Zr) for titanium results in decrease in non-centrosymmetric tetragonal to centrosymmetric cubic phase transition temperature (Curie temperature). Whereas substituent like lead (Pb) for barium results in the increase in the Curie temperature. Here we are reporting effect of lanthanum (La) substitution on the properties of Zr and Pb co-substituted BT. The system Ba0.80−xLaxPb0.20Ti0.90Zr0.10O3 with x = 0 and 0.01 was selected for study of structural and dielectric properties. Samples were prepared using solid state ceramic route. X-ray diffraction studies (XRD) were used to confirm single phase structure. Dielectric properties were studied as a function of frequency and temperature. Composition with x = 0.01 was found to show relaxor behavior.
Journal of Materials Science, 2012
Dielectric and piezoelectric responses are investigated in relaxor-like lanthanum-modified lead zirconate titanate (PLZT) ceramics, for a La/Zr/Ti ratio of x/60/40 (x = 8 and 10 at.%), obtained by the conventional ceramic method. No significant differences were observed from the room temperature ferroelectric properties, for both PLZT compositions. On the other hand, from evaluation of the nonlinear dielectric response in terms of the Rayleigh's model, a typical 'soft' behaviour is achieved in both materials, although the increments of the dielectric losses are slightly higher than the predicted by this model. The piezoelectric coefficient shows a remarkable increment with the applied dynamics stress, nevertheless without noticeable differences as a function of the lanthanum concentration. However, a significant difference is displayed in the weak-field direct longitudinal piezoelectric response. The dielectric properties revealed a higher diffuseness degree of the phase transition for the highest lanthanum content composition (PLZT 10/60/40). Thus, the observed difference in the piezoelectric response is discussed based on the nature of the phase transition in the studied relaxor materials.
Dielectric dispersion of the relaxor PLZT ceramics in the frequency range 20 Hz100 THz
Journal of Physics-condensed Matter, 2000
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.