PMN-PT ceramics

Fig. 7.9 shows the temperature dependence of the dielectric constant and dielectric loss at 1 kHz for the PMN-PT ceramics obtained by sintering the calcined powders from a soft-mechanochemical route at 1200°C for 2 h. A diffuse phase transition, being typical for a relaxor, is observed for each ceramics. As x increases from 0 to 0.2, the maximum dielectric constant, K, , increases from 13000 to 27000. The temperature correspondent to K ,... 

Kong LB, Ma J, Zhu W, Tan OK (2002) Translucent PMN and PMN-PT ceramics from high-energy ball milling derived powders. Mater Res Bull 37 23-32... 

Figure 10.13 shows experimental setup for the optical characteristic measurement of PMNT ceramics [133]. The size of PMN-PT ceramic sample was 5 mm X 2 mm x 1 mm for length x width x thickness. Ti/Pt/Au layers were sputtered on both surfaces of the ceramics as electrodes. Two collimators were used to collimate the incident beam and receive the transmission beam. The output beam was detected by using an optical spectrometer and phase demodulation. Because the PMN-PT electro-optic ceramics have a large refractive index, i.e., n = 2.465, the ceramic samples could be considered as a Fabry-Perot (FP) resonator, which can be used to measure the electric hysteresis and thermo-optic coefficient. The applied voltage generated a transverse electro-optic effect for the transmission light beam. 

Figure 10.14 shows the variation of phase shift of incident beam of the PMN-PT ceramic samples, as a function of the applied voltage [133]. A quadratic curve... 

There is also growing iaterest ia thin-film dielectric capacitors. For example, through the use of processiag techniques such as sol—gel solution deposition, thin (--- 0.25 fim) ceramic layers having dielectric constants ranging from 500 to 2000 ia the PZT, Pb(Zr,Ti)03, and PMN—PT, Pb(Mn2 3Nb2 3)03-PbTi03, compositional families respectively, have been prepared (3). 

Pyro- and Piezoelectric Properties The electric field application on a ferroelectric nanoceramic/polymer composite creates a macroscopic polarization in the sample, responsible for the piezo- and pyroelectricity of the composite. It is possible to induce ferroelectric behavior in an inert matrix [Huang et al., 2004] or to improve the piezo-and pyroelectricity of polymers. Lam and Chan [2005] studied the influence of lead magnesium niobate-lead titanate (PMN-PT) particles on the ferroelectric properties of a PVDF-TrFE matrix. The piezoelectric and pyroelectric coefficients were measured in the electrical field direction. The Curie point of PVDF-TrFE and PMN-PT is around 105 and 120°C, respectively. Different polarization procedures are possible. As the signs of piezoelectric coefficients of ceramic and copolymer are opposite, the poling conditions modify the piezoelectric properties of the sample. In all cases, the increase in the longitudinal piezoelectric strain coefficient, 33, with ceramic phase poled) at < / = 0.4, the piezoelectric coefficient increases up to 15 pC/N. The decrease in da for parallel polarization is due primarily to the increase in piezoelectric activity of the ceramic phase with the volume fraction of PMN-PT. The maximum piezoelectric coefficient was obtained for antiparallel polarization, and at < / = 0.4 of PMN-PT, it reached 30pC/N. 

Lam et al. [2005] also reported the evolution of the pyroelectric coefficient (pe) with the volume fraction of PMN-PT. The pyroelectric coefficients of ceramic and copolymer have the same sign, but not their 33 coefficients. The maximum increase was obtained for a parallel polarization procedure. In both cases, the increase was quasilinear as a function of filler content from 5 to 40% of PMN-PT to 40%, the pyroelectric coefficient, pe, increased by a factor of 3. A linear increase in the piezoelectric coefficients of composites has also been shown in a PA-11/BT system [Capsal et al., 2007]. It was found that BT particles increase the piezoelectricity of the composite up to 6pC/N for piezoelectric activity with decreasing filler size, due to the decrease in tetragonality (ferroelectric phase). 

Ceramic PLZT has a number of structures, depending upon composition, and can show both the Pockels (linear) electro-optic effect in the ferroelectric rhombohedral and tetragonal phases and the Kerr (quadratic) effect in the cubic paraelectric state. Because of the ceramic nature of the material, the non-cubic phases show no birefringence in the as-prepared state and must be poled to become useful electro-optically (Section 6.4.1). PMN-PT and PZN-PT are relaxor ferroelectrics. These have an isotropic structure in the absence of an electric field, but this is easily altered in an applied electric field to give a birefringent electro-optic material. All of these phases, with optimised compositions, have much higher electro-optic coefficients than LiNb03 and are actively studied for device application. 

The typical representatives of this family include Pbi La (ZryTii y)i /403 (PLZT), Pb(Mgi/3Nb2/3)03-PbTi03 (PMN-PT), and Pb(Zny3Nb2/3)03-PbTi03 (PZN-PT). The PLZT formula assumes that La substitutes for Pb " in the A-site and the B-site vacancies are created for electrical balance. To achieve highest transparency and electro-optic coefficient, some elements, such as Ba and/or La, are usually introduced into the solid solutions of PMN-PT and PZN-PT. Material synthesis and properties of transparent electro-optic ceramics, including PLZT and PMN-PT, have well been summarized and documented [223]. 

Detailed investigation on the optical characteristics, including the electro-optic phase modulation, electric hysteresis property, and thermo-optic coefficient, of transparent PMN-PT electro-optic ceramics have been conducted [229]. A polarization independent PMNT electro-optic switch by using s -shifted fiber Sagnac interferometer stmcture was constracted and analyzed experimentally. Some switch performances, including thermal characteristic and different switching frequency response, were also realized. 

Preparation and characterization of transparent ceramics of La-doped PMN-0.25PT by a two-stage sintering method from conventional raw materials were reported in Ref. [236]. Optical characteristics of Er -doped PMN-PT transparent... 

Fig. 7.13 Transmission curves of the PMN-PT 3/75/25 ceramics with a thickness of 0.5 mm (a) and SEM images of the samples sintered with different schedules b sample A, c sample B, and d sample C. Reproduced with permission from [59]. Copyright 2010, John Wiley Sons...

Landolt-Bomstein Tables, Neue Serie Vol. lll/30b. Springer Verlag. Gurzadyan GG, Charra F (2000) High Fiequeney Properties of Dielectrie Crystals. Nonlinear Dieleetric Susceptibilities. Lee S-H, Roh Y (2007) Characterization of all the elastic, piezoelectric, and dielectric constants of tetragonal PMN-PT single crystals, Jpn J Appl Phys 46, 7B 4462 465 Levinson LM (1988) Electronic ceramics - Properties, Devices and Applications. Marcel Dekker, New York, NY... 

The development of characterization and fabrication methods approaching the unit-cell size of known piezoelectric materials has reenergized the area of piezoelectric materials research in the past few years. By tailoring the structure of piezoelectric materials to maximize the polarizability, strength, and maximum strain, major advances are just beginning to appear. Work on applying the replete knowledge of bulk piezoelectric materials to thin-film materials research remains incomplete, from fabrication of PMN-PT to lead-free ceramics at small scales. 

It should be mentioned that the otherwise transversely isotropic properties of the typical piezoelectric materials, given by Table A.3 in the Appendix, show deviations of a different degree from the last relation of Eqs. (4.3) expressing the dependence of C. While these deviations are relatively small in the case of the PZT ceramics, the properties of PMN-PT single crj tals do not comply with this condition at all. 

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