The microstructural evolution and piezoelectric properties of lead-free ceramics (0.98-x)(Na0.5Bi0.5)TiO3–x(Na0.5K0.5)NbO3–0.02BaTiO3 (0 ⩽ x ⩽ 0.98, abbreviated as (0.98-x)NBT–xNKN–0.02BT) were investigated. The effects of the amount of NKN on the crystal structure, microstructural evolution, and piezoelectric properties were examined. The 0.93NBT–0.05NKN–0.02BT ceramics having a lower NKN content gave good performances with piezoelectric properties of d33 = 140 pC/N and kp = 21%, because of the soft additive Nb5+ ions at the B sites. However, a paraelectric cubic phase was observed in the wide range of compositions between x = 0.1 and x = 0.9. At a higher NKN content of x > 0.9, a morphotropic phase boundary (MPB) between the tetragonal and orthorhombic phases was found in the 0.015NBT–0.965NKN–0.02BT ceramics, and the piezoelectric properties were enhanced (d33 = 135 pC/N, kp = 29%). The piezoelectric properties of this system were closely related to its crystal structure.

Highly dense and crack-free Pb(Zr,Ti)O3 (PZT) thick films with a controlled microstructure and orientation were deposited on a platinized silicon substrate by the radio frequency magnetron sputtering method using a single oxide target. The microstructure and orientation of the films were adjusted by applying a thin (100) PZT seed layer by the sol-gel method and subsequent repeated sputtering. When a thin layer was deposited on the seed layer, the film had small grains with a columnar structure. However, as the film became thicker, it developed a large and non-columnar grain structure. Therefore, reducing the thickness of the film per deposition allowed the columnar microstructure to be maintained. The (100) orientation of the film was able to be maintained by depositing it on a (100) oriented seed layer. PZT thick films with controlled orientations and microstructures were successfully deposited up to a thickness of about 5 μm, and their ferroelectric and piezoelectric properties were characterized.

Thick and crack-free Pb(Zr,Ti)O3 [PZT] films were fabricated on platinized silicon substrates by a multisputtering technique. The PZT films were deposited on the Si substrate by the radio frequency magnetron sputtering method using a single oxide target. As the film became thicker, its grain size increased. Therefore, the microstructure of the film was able to be controlled by repeatedly depositing thin layers. In addition, by using a seed layer with the same composition but a much smaller grain size, it was possible to further reduce the grain size of the film. When the film had a small in-plane grain size and a fibrous columnar structure, it was highly resistant to cracking, presumably because of its enhanced strength and structural stability. By exploiting these phenomena, highly dense, crack-free, and thick PZT films were successfully deposited up to a thickness of about 5 μm. The evolution of the crystallographic orientation of the film as a function of its thickness was also observed and correlated with the total strain energy of the system.

Highly (100)- and (111)-oriented lead magnesium niobate–lead zirconate titanate (PMN-PZT) films were deposited on Pt(111)/Ti/SiO2/Si substrates using a sol containing polyvinylpyrrolidone (PVP). The molar ratio of Zr/Ti in the PZT was fixed at 60/40, and the PMN content was changed in the range of 0–30 mol%. The films had a dense and columnar microstructure with a thickness of about 1 μm as a result of being spun four times. The crystallographic orientation of the films was controlled by adjusting the pyrolysis temperature; a (100) orientation was obtained by pyrolyzing at 300 °C and a (111) orientation by pyrolyzing at 350 °C. The electrical properties of the films were strongly dependent on the crystallographic orientation and PMN content. With increasing PMN content, the dielectric constant of all of the films increased. On the other hand, the remnant polarization of the (111)-oriented films decreased steadily with increasing PMN content, while that of the (100)-oriented films remained unchanged up to a PMN content of 20%. The piezoelectric coefficients of the (100)-oriented film were consistently higher than those of the (111)-oriented film with the same composition. The highest piezoelectric coefficient was observed for the (100)-oriented film with a composition of 0.2PMN–0.8PZT, indicating the morphotropic phase boundary between the rhombohedral PZT phase and the pseudocubic PMN phase is in the vicinity of this composition.

The effects of residual stress induced during the annealing process on the microstructural evolution and electrical properties of Pb(Zr,Ti)O3 (PZT) films were investigated. PZT films were deposited on platinized silicon substrates by the radio frequency magnetron sputtering method using a single oxide target. Compressive stress was induced in the film by bending the silicon substrate during sputtering using a specially designed substrate holder and subsequently annealing the film without the holder. Without the residual stress, the PZT film was severely cracked when it was thicker than 2 μm due to the thermal expansion mismatch between the PZT and the Si substrate. On the other hand, when the residual stress was applied, no cracks were detected in the film for thicknesses of up to 4 μm. The suppression of crack formation was attributed to the residual compressive stress that compensated for the tensile stress generated during and/or after the annealing process. The electrical properties of the PZT film with the residual stress were improved compared to those of the PZT film without the residual stress.

Highly (100)- and (111)-oriented lead zirconate titanate (PZT) films with a thickness of 350 nm were deposited on platinized Si substrates through a single spinning of a PZT sol containing polyvinylpyrrolidone (PVP) as an additive. The crystallographic orientation of the film was strongly influenced by pyrolysis conditions after spin coating. When the spin-coated sol was pyrolyzed at temperatures above 320 °C for relatively long periods of time (>5 min), (111)-oriented film was formed after annealing at 700 °C for 10 min. On the other hand, when the same sol was pyrolyzed at 320 °C for short periods of time (<5 min), the film was strongly oriented to the (100) direction after annealing. Organic residues derived from PVP decomposition acted as nucleation sites for the (100) oriented grains during annealing after the pyrolysis. The effective d33 of the (100)-oriented PZT film (100 pC/N) was much higher than that of the (111)-oriented film (62 pC/N) with the same thickness.

The orientation and electrical properties of Pb(Zr,Ti)O3 thin films deposited on a Pt/Ti/SiO2/Si substrate using lanthanum nickel nitrate as a conductive buffer layer were analyzed. The lanthanum nickel nitrate buffer layer was not only electrically conductive but also effective in controlling the texture of the lead zirconate titanate (PZT) thin film. The role of the lanthanum nickel nitrate buffer layer and its effects on the orientation of the PZT thin film were analyzed by x-ray diffraction, electron beam back-scattered diffraction, and scanning electron microscopy. The annealed lanthanum nickel nitrate buffer layer was sufficiently conducting for use in longitudinal electrode configuration devices. The dielectric, ferroelectric, and piezoelectric properties of the highly (100) oriented PZT films grown with the lanthanum nickel nitrate buffer layer were measured and compared with those of (111) and (100) oriented PZT films deposited without a buffer layer.

Highly (100) oriented Pb(Zr,Ti)O3 [PZT] films were fabricated using lanthanum nitrate/nickel acetate double layers as a buffer layer, regardless of the other deposition conditions, such as the pyrolysis temperature, pyrolysis time, annealing temperature, and heating rate. The buffer layer was also acted as a very effective barrier against Pb-Si interdiffusion, thus allowing for the direct deposition of PZT films on Si, SiO2/Si, and glass substrates. The strong orientation was attributed to the formation of a crystalline intermediate phase between the PZT and lanthanum nitrate during annealing. The lanthanum nitrate/nickel acetate double layers became a lanthanum nickel oxide (LaNiO3), which shows good electrical conductivity, after an annealing process at 650°C. The nature and the role of lanthanum nitrate buffer as a layer for the growth of highly (100) oriented PZT films have been studied. The dielectric, ferroelectric, piezoelectric and electrooptic properties of the highly (100) oriented PZT films with a lanthanum nitrate/nickel acetate buffer layer were measured and compared with the values measured from the (111) and (100) oriented PZT films deposited without buffer layer.

Highly oriented lead zirconate titanate (PZT) films were fabricated on a platinized silicon substrate using a combination of sol-gel and radio frequency (RF) magnetron sputtering deposition methods. A sol-gel derived PZT layer highly oriented to the (100) plane was deposited as a seed layer, and PZT with the same composition then was deposited on the seed layer by RF-magnetron sputtering. The film deposited on the seed layer showed a strong (100) preferred orientation, while the film deposited without the seed layer showed a (111) preferred orientation. Furthermore, a thick PZT film of up to 4 μm was able to be deposited without cracks by using the seed layer. The piezoelectric property of the (100) oriented film was much better than that of the (111) oriented film.

Highly oriented Pb(Zr,Ti)O3 (PZT) films were deposited on Pt/Ti/SiO2/Si substrates by the sol-gel method using lanthanum nitrate as a buffer layer. When the lanthanum nitrate buffer layer was heat treated at temperatures between 450 and 550 °C, the PZT layer coated onto this buffer layer showed a strong (100) preferred orientation. Regardless of the other deposition conditions, such as the pyrolysis temperature, pyrolysis time, annealing temperature and heating rate, the film deposited on the buffer layer had this orientation. Thick films were also fabricated using the sol-gel multi-coating method, and the (100) texture was found to be maintained up to a thickness of 10 μm. The ferroelectric hysteresis and piezoelectric coefficient (d33) of highly oriented PZT thick films were characterized, and the (100) oriented PZT film showed higher piezoelectric property than the (111) oriented film.

Materials with preferred orientation exhibit unique properties that are frequently improved in comparison with those that are randomly oriented. Optical waveguide devices require high-quality single-crystal–like thin films because of their low optical propagation loss and their near–single-crystal properties. The growth mechanisms of textured films on non-lattice matched amorphous substrates, such as glass, are different from those on single-crystal substrates or the surface of a metal electrode. In this study, highly (100) oriented Pb(Zr,Ti)O3 PZT films were grown on an amorphous substrate by means of the sol-gel multicoating method, using lanthanum nitrate as a buffer layer. The lanthanum nitrate buffer layer was also very effective as a diffusion barrier against Pb-Si interdiffusion. The electrooptic properties of the PZT films were markedly enhanced when their orientation was adjusted to the (100) direction.

We investigated the effect of lead zinc niobate (PZN) on the sintering behavior and piezoelectric properties of lead zirconate titanate (PZT) ceramics. The addition of PZN improved the sinterability of PZT ceramic so remarkably, that at additions of more than 10%, the specimens were fully dense at a temperature as low as 900 °C. The phase of the PZT-PZN ceramics was affected by PZN content and the Zr/Ti ratio in the PZT. With increasing PZN content, a lower Zr/Ti ratio was required for the morphotropic phase boundary (MPB). Specimens with the MPB composition showed the highest piezoelectric properties; d33 = 500 pC/N, kp = 0.68, and S33 = 0.38% at 2 kV/mm.

Macrochannelled tetragonal zirconia polycrystals (TZP) coated with a calcium phosphate layer were fabricated using a coextrusion process to produce strong and bioactive porous bioceramics. The initial feedrod, composed of three materials [TZP (shell), calcium phosphate (intermediate layer), and carbon black (core)], was coextruded through a 750-μm orifice at 120 °C, producing a continuous and flexible filament. Each sheet, which was composed of a unidirectional array of filaments, was stacked and then warm-pressed at 140 °C with 10 MPa. After binder burnout, the green billet was sintered between 1350 and 1600 °C for 1 h in air, leaving uniform macrochannels clad on the inside with bioactive calcium phosphate on a strong TZP body. The compressive strength of the specimen was much higher than that of calcium phosphate with a similar structure.

The effect of lanthanum (La) addition on the piezoelectric properties of lead zirconate titanate–lead zinc niobate (PZT–PZN) was investigated. When small amounts of La were added to the 0.82PZT–0.18PZN, the phase of the specimen changed from rhombohedral to tetragonal and the grain size was steadily reduced. To retain the morphotropic phase boundary (MPB) condition of the specimens with La contents of up to 4 mol%, the Zr/Ti ratio in the PZT was increased to 54/46. When more than 5 mol% La was added, pyrochlore phases were formed, and the piezoelectric properties were reduced. Therefore, the optimum piezoelectric properties (d33 = 545 pC/N, kp = 0.64, and s33 = 0.39% at 2 kV/mm) were observed in the specimen having MPB composition and with an La content of 4 mol%.

To improve the oxidation resistance of Si3N4 material, a dense and continuous layer, composed of small Y2Si2O7 crystallites and silicate glass, was formed on the surface. The surface layer was formed by exposing the specimens in a flowing H2 atmosphere containing 0.1% H2O at 1450 °C for 1 h. For the purpose of comparison, specimens of the same material were heat treated in air at 1450 °C for 1 h. Small equiaxed Y2Si2O7 crystallites were formed when the specimen was heat treated in the wet H2 atmosphere, while relatively large and elongated Y2Si2O7 crystallites developed when the specimens were heat treated in air. The oxidation resistance of Si3N4 material was improved remarkably by the heat treatment in the wet H2, while no improvement in oxidation resistance was observed from the specimen heat treated in air. The improvement was attributed to the retardation of the transport of oxidants through the dense and continuous layer formed on the surface.

The piezoelectric and dielectric properties of Pb(Zn1/3Nb2/3)O3 (PZN)-based ceramics were investigated. The perovskite structure of PZN ceramics was stabilized by the addition of Pb(Zn0.47Ti0.53)O3 (PZT). The highest piezoelectric properties were observed for the composition of 0.5PZN–0.5PZT, which lies on the two-phase zone of morphotropic phase boundary. For further improvements in electric properties, the specimens were thermally treated in a flowing O2 atmosphere at temperatures ranging from 860 to 1030 °C. The thermal treatment eliminated the PbO-rich amorphous intergranular layer by lead evaporation. As a result of this improvement in structure, the dielectric constant (ε′), the piezoelectric coefficient (d33), and the electromechanical coupling factor (kp), were enhanced markedly after thermal annealing at 960 °C for 8 h in an O2 atmosphere.

To improve the oxidation resistance of TiB2 material, dense silica (SiO2) layer was caused to form on the surface. The coating layer was formed on the surface by exposing the specimens next to a bed of SiC powder in a flowing H2 containing 0.1% H2O at 1450 °C. Part of SiO2 “smoke”, generated by a reaction between the SiC powder and H2O in the H2 gas stream, was deposited on the sample surface to form a dense and uniform SiO2 layer. Beneath the SiO2 layer, an interfacial layer composed of Ti2O3 and B2O3was formed. Oxidation resistance of the specimen was improved markedly by the coating layers. The coating layers enhanced the oxidation resistance through the retardation of oxygen transport and also through the consumption of oxygen by a reaction with Ti2O3 to form TiO2.

The effect of ZrO2 addition on sintering behavior and mechanical properties of both hot-pressed and pressureless-sintered B4C was investigated. The addition of ZrO2 improved the densification behavior of B4C remarkably via a reaction with the B4C to form ZrB2 at elevated temperatures. When B4C was densified at 2000 °C by hot pressing, only a small amount (approximately 2.5 vol%) of ZrO2 was necessary to achieve a full densification. Excellent mechanical properties (hardness, elastic modulus, flexural strength, and fracture toughness) were observed in those specimens. As the amount of ZrO2 was increased further, the mechanical properties were reduced, except for the fracture toughness, apparently due to the formation of too much ZrB2 in the specimen. Without the applied pressure, larger amounts of ZrO2 should be added to obtain a body with high relative density. When the B4C was sintered at 2175 °C with addition of 10 vol% ZrO2, the specimen has a density higher than 95% of the theoretical, and hardness and flexural strength of 25 GPa and 400 MPa, respectively.

The oxidation behavior and the effect of oxidation on the flexural strength of Si3N4/SiC nanocomposites were investigated. Parabolic weight gains, with respect to the oxidation time, were observed for all the specimens containing different amounts of SiC. However, the parabolic rate constant decreased with increasing SiC content. The main oxidation product, being in equilibrium with SiO2, was Y2Si2O7. The oxidation product became denser and retained more crystalline phase as the amount of SiC increased. The flexural strength of the nanocomposites increased by up to 40%, while that of pure Si3N4 decreased after oxidation at 1300 or 1400 %C for 100 h. This excellent oxidation resistance of Si3N4 nanocomposite was attributed to the enhancement of the crystallization of the oxidation product and the grain boundary phase by the SiC nanoparticles.

The effects of SiC-nanoparticle and Si3N4-whisker additions on the microstructural evolution and mechanical properties of Si3N4 were investigated. The addition of SiC nanoparticles suppressed Si3N4 grain growth, leading to an improvement in the flexural strength. On the other hand, Si3N4 whiskers in the specimen promoted the formation of large elongated grains, which were found to be beneficial to the fracture toughness of the material. When both SiC nanoparticles and Si3N4 whiskers were added concurrently, large grains were formed in fine matrix grains. The microstructure of Si3N4 was controlled by adjusting the relative concentrations of SiC nanoparticles and the Si3N4 whiskers added. These compositional and microstructural variations of the Si3N4 had significant influence on the mechanical properties, such as strength, fracture toughness, R-curve behavior, and high-temperature strength.