Lead titanate sintering

Electroceramics. Titanates like barium, strontium, calcium and lead titanate prepared from finely divided, high-purity TiOz hydrolysates are used in capacitors, PTC-resistors and piezoelectric materials. The specifications of the Ti02 starting materials with respect to purity, reactivity, and sintering properties are expected to become more stringent. The market is estimated to be several thousand of tonnes a year as TiOz. A strong annual growth is expected. 

Takeuchi, T., Tabuchi, M., Kondoh, I., Tamari, N., Kageyama, H., (2000), Synthesis of dense lead titanate ceramics with submicrometer grains by spark plasma sintering , J. Am. Ceram. Soc., 83, 541-544. 

Zhou LJ, Zhao Z, Zimmermann A, Aldinger F, Nygren M (2004) Preparation and properties of lead zirconate stannate titanate sintered by spark plasma sintering. J Am Ceram Soc 87 606-611... 

Powders from Alkoxides and Salts. Two solutions were prepared individually for the synthesis of lead titanate (PbTiOs) particles by Tartaj et al. (2001) (i) titanium tetra-butoxide in 2-propanol, and (ii) lead acetate in glacial acetic acid. The solutions were mixed under stirring, and a water-2-propanol mixture added to this for the initiation of hydrolysis. As in some other cases, crystalline seeds of the target compound, suspended in 2-propanol, were added (10 wt%) to the transparent sol already obtained. The gels obtained through this process were dried and ground to small particles and calcined at 400°C for 20 h for use in the preparation of sintered bodies. X-ray diffractometry of the calcined sample showed it to be fully crystallized to phase-pure PbTiOs, while an unseeded sample did not crystallize under the same conditions. 

Tartaj J., Moure C, Lascano L., Duran P. Sintering of dense ceramics bodies of pure lead titanate obtained by seeding-assisted chemical sol-gel. Mater. Res. Bnll. 2001 36 2301—2310 Traversa E., Di Vona M.L., Licoccia S., Sacerdoti M., Carotta M.C., Gallana M., Martinelli G. J. Sol-Gel Sci. Technol. 2000 19 193-196... 

SINTERING OF SOI GEL DERIVED PURE AND DOPED BINARY OXIDES Sintering of Lead Titanate... 

S. Venkataramani, Calcining and Its Effects on Sintering and Properties of Lead Zirconate Titanate Ceramics, Ph.D. thesis, Pennsylvania State University, 1981. 

Sintered ceramics made of lead-zirconium titanate (PZT Pb(Tii jZr,)03 x S 0.5) are usually used for phoioacoustic experiments [105, 106]. The unit cell of the lead-zirconium titanate has a perovskite structure. Below the Curie temperature (328 °C for the PZT-4 (Vemitron) used by us [24]), the cells are tetragonally deformed, i.e., positive and negative charges are shifted and electric dipole moments are produced. In analogy to ferromagnetism, domains with randomly distributed polarization direction are formed. By the application of an electric field, these can be orientated in a preferred direction, and the sintered polycrystalline ceramic is then remanently polarized. The properties of these anisotropic piezoelectric materials are described by various parameters which depend on the polarization and deformation direction. In the common terminology, the < ordinate system shown in Fig. 3 is obtained for the cylindrical piezoelectric crystals [24]. 

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. 

Abe Y, Kakegawa K (2002) Fabrication of optically transparent lead lanthanum zirconate titanate ((Pb, La)(Zr, Ti)03) ceramics by a three-stage-atmospheie-sintering technique. J Am Ceram Soc 85 473-475... 

In addition to the multilayered ceramic capacitors just described, many of the barium titanate-based compounds that exhibit high dielectric constants are used in single-layer tape-cast capacitor devices. Relaxor materials such as lead magnesium niobate (PMN), which are characterized by high dielectric constants, broad dielectric maxima, and low sintering temperatures, have been manufactured in thin sheets by tape casting. 

A special class of materials that is also ferroelectric are electrooptic ceramics. Materials such as lanthanum-modified lead zirconate titanate (PLZT) produce excellent electrooptic devices. These polycrystalline ceramics exhibit voltage-variable behavior—that is, they can be switched from optically transparent to opaque by the application of voltage. Most of these devices, which are used for shutters, modulators, and displays, are processed by hot pressing to full density. Experiments in many laboratories are being carried out to tape-cast these materials into thin sheets. The main problem encountered to date has been the ability to sinter to full density. The use of nanosized powders has helped in this regard. The ability to tape-cast large sheets could open a wide variety of applications for these materials. 

Lead is poisonous, so that in addition to controlling the lead loss, the evaporated lead must be contained. In practice, this is achieved by surrounding the sample with lead-based powder compositions (31), such as a mixture of PbO and PbZrOs for lead-lanthanum-zirconium titanate (PLZT), to provide a positive vapor pressure in a closed AI2O3 crucible (Fig. 12.22). With the controlled atmosphere apparatus, PLZT can be sintered to full density (Fig. 12.23), yielding materials with a high degree of transparency. 

K. G. Ewsuk. The Effects of Hot Isostatic Pressing on Microstructure and Properties of Sintered Lead Zirconate Titanate. M.S. dissertation, Pennsylvania State University, University Park, 1982. 

---