PLZT ceramics

The sintering atmosphere is demonstrated to be important in determining the final microstructure of the PLZT ceramic because of the volatility of lead oxide (PbO). A controlled oxygen partial pressure sintering method was established to obtain transparent (Pb, La)(Zr, Ti)03 ceramics [224]. PLZT(7/60/40) ceramics with large piezoelectric coefficients were prepared by using a two-step sintering process 

Pressure sintering techniques have also been used to fabricate transparent lanthanum-doped lead zirconate titanate (PLZT) ceramics in air and in oxygen-gas atmosphere [31]. The microstructure of the sintered body was not uniform it was completely dense near the surface, but it was porous at the center. The thickness of the dense layer increased with sintering time and oxygen-gas pressure in the sintering atmosphere. Vaporization of PbO from the specimen surface and resultant formation of lattice vacancies were attributed to this microstructural evolution. Diffusion of the gas trapped in the pores was also important in determining the thickness of the dense layer. When the PLZT specimen was sintered in air at 1200 °C for 8 h, the thickness of the dense layer was 0.25 mm. Therefore, if the specimen thickness was 0.5 mm, the whole specimen was dense and transparent. When the specimen was sintered in an oxygen-gas atmosphere under the same conditions, the specimen thickness increased markedly. 

A simple and feasible repeated annealing process was available to obtain transparent PLZT(9/65/35) ceramics [226]. The experiment was started from nanosized powder of PLZT, which was synthesized directly from commercially available constituent oxides by using a high-energy ball milling at near room temperature. Transparent PLZT ceramics were obtained by annealing the samples 

SPS has been confirmed to be a viable technique to synthesize PLZT transparent ceramics. An example is the preparation of PLZT(8/65/35) ceramics [227]. The PLZT powder was synthesized by using a wet-dry combination method. Due to the contamination of carbon from the graphite mold, the samples after the SPS sintering should be annealed in air or oxygen. Optical properties of the samples were affected by the SPS temperature, as well as the post-annealing temperature. It was found that 700 °C was the optimal sintering temperature when transmittance was considered. 

---

Figure 3. Various stages in the processing of PLZT ceramics...

Figure 4. A typical setup for hot pressing PLZT ceramics...

Figure 5. Examples of the optical transparency of quadratic PLZT ceramics...

Depending on composition PLZT ceramics display one of three major types of electro-optic characteristic, i.e. memory , linear or quadratic . These are shown in Fig. 8.11, together with the corresponding hysteresis loops, and are discussed briefly below. 

Convenient sol-gel processing, compaction, and firing allow the synthesis of optically clear ceramics. Two examples are presented in Figure 12.6, a ferroelectric PLZT 65/35 ceramic prepared by hybrid sol-gel route and a mulhte matrix prepared using aluminum-sihcon ester and silicon-methoxide. Note the opaque skin around the transparent PLZT ceramics is related to PbO loss. When a partial pressure higher than the equihbrium pressure required to avoid any PbO excess... 

PLZT ceramics display optically uniaxial properties on both a microscopic and a macroscopic scale once polarized. The optic axis coincides with the polarization. 

Depending on composition PLZT ceramics display one of the three major types of EO characteristics shown in Eigure 32.22. 

Here we will briefiy describe four applications for PLZT ceramics. 

Haertling, G.H. and Land, C.E. (1971) Hot-pressed (Pb,La)(Zr,Ti)03 ferroelectric ceramics for electrooptic applications, J. Am. Ceram. Soc. 54, 1. This is the original citation for transparent PLZT ceramics. Kaiser, P. (1973) Spectral losses of unclad fibers made from high-grade vitreous silica, Appl. Phys. Lett. 23, 45. Developed the MCVD process. 

PLZT ceramics belonging to either the tetragonal or rhombohedral crystal systems are classified as optically uniaxial. Which other crystal system or systems are also optically uniaxial ... 

Choi JJ, Ryu J, Kim HE (2001) Microstmctural evolution of transparent PLZT ceramics sintered in air and oxygen atmosphraes. J Am Ctaam Soc 84 1465—1469... 

The milled powder was then pressed uttiaxially into 10 mm diameter pellets. The green pellets of about 70 % of the theoretical density were sintered in air for 4 h at temperatures from 900 to 1000 °C, with both heating and cooling rate being 10 °C ntin. Transparent PLZT ceramics could be obtained by annealing the... 

Fig. 3.13 Cross-sectional SEM images of the PLZT ceramics derived from the milled oxide mixture sintered for 4 h at different temperatures a 900 °C, b 925 °C, c 950 °C and d 1000 °C. Reproduced with permission from [90], Copyright 2001, Elsevier...

Kong LB, Ma J, Zhu W, Tan OK (2001) Preparation and characterization of PLZT ceramics using high-energy ball milling. J Ahoy Compd 322 290-297... 

---