Ulagaraj Selvaraj

Sol-gel processing of PbTiO 3 and Pb(Zr 0.52 Ti 0.48 )O 3 fibers

Homogeneous and stoichiometric PbTiO 3 and PbZr 0.52 Ti 0.48 O 3 gel fibers were drawn from viscous solutions prepared by sol-gel processing of alkoxide precursors. The fibrous gels on heating at 450 and 600 °C, respectively, formed the well-crystallized phases of PbTiO 3 and PbZr 0.52 Ti 0.48 O 3 . Fibers heat treated at 700 °C are a few centimeters long and 50 to 150 μm in diameter. PbZr 0.52 Ti 0.48 O 3 fibers subjected to heat treatment at 700 °C for 1 h consisted of fully dense submicron grains (0.15 to 0.2 μm). However, PbTiO 3 fibers under analogous conditions showed a few micropores with grains of ∼0.1 μm. Dielectric constants of these PbTiO 3 and PbZr 0.52 Ti 0.48 O 3 fibers were approximately 300 and 800, respectively.

Sol-gel synthesis of Ln 2 (Ln = La, Nd)Ti 2 O 7

Lanthanum and neodymium titanates were prepared by a sol-gel route. Synthesis of La2Ti2O7 from pure alkoxide precursors yielded an intermediate perovskite type phase, La(1–x)TiO3, which partially transformed to La2Ti2O7 on heating to 1500 °C. Substitution of the lanthanum acetylacetonate for alkoxide precursor yielded La2Ti2O7 without any intermediate phase at a very low temperature of 700 °C. Sintering of the La2Ti2O7 gel powder yielded a highly dense ceramic with ∼97% theoretical density. Similar sintering treatment resulted in ∼92% theoretical density for Nd2Ti2O7.

Nanocomposite aerogels : the SiO2-Al2O3 system

Monolithic nanocomposite aerogels of two aluminosilicate compositions have been prepared and characterized by different techniques. The results show that high surface area and mesoporosity can be preserved in the above nanocomposite aerogels by heating at 1000 °C, unlike the single component aerogels. The presence of alumina as a second phase prevented their densification which resulted in surface areas on the order of 500–600 m 2 /g and mesopores of about 5–6 nm in diameter after heat treatment at 1000 °C. These novel nanocomposite aerogels are expected to find applications at high-temperatures in separations, insulation, catalysis, etc.

Grain orientation in sol-gel derived Ln2Ti2O7 ceramics (Ln = La, Nd)

Sol-gel derived La2Ti2O7 and Nd2Ti2O7 exhibited preferential grain orientation on sintering. The extent of orientation is quantified in terms of the Lotgering orientation factor from the XRD intensities of pellets sintered at different temperatures. The microstructural studies indicated extensive orientation with sintering and also a change in morphology of the grains from acicular to large platelets.

Sol-gel processing of oriented SrTiO3 thin films

Abstract Sol-gel processing was employed to fabricate multilayered SrTiO3 thin films onto fused silica, Si (100) and SrTiO3 (110) substrates. A Sr-Ti alkoxide precursor solution, chemically modified with diisopropanolamine, was hydrolyzed and spin-coated onto these substrates. These films were annealed at 300 °C and then heated to 650 °C for 1 h in air, which resulted in the formation of phase pure crystalline SrTiO3. X-ray diffraction analysis indicated that partially oriented films were deposited onto fused silica and Si (100), while highly oriented film was formed on SrTiO3 (110). A typical microstructure of the film deposited on SrTiO3 (110) and heated at 650 °C for 1 h showed the presence of submicrometer grains on the order of 0.05 to 0.1 μm. The thickness of a single coating measured from the cross section of the SEM micrograph was about 0.1 to 0.2 μm.

Sol-gel processing of oriented PbTiO3 thin films with lead acetylacetonate as the lead precursor

Abstract Sol-gel lead titanate thin films were spin-coated onto MgO(100), platinum-coated silicon, SrTiO 3 (211) and SrTiO 3 (100) substrates. This method utilizes lead acetylacetonate as the lead precursor instead of the widely used lead acetate trihydrate, along with titanium iso-propoxide. The use of lead acetylacetonate yielded a more stable precursor solution as compared to that of lead acetate trihydrate. Lead titanate crystallized at a temperature as low as 425°C, which is considerably lower than the Curie temperature. Films deposited on various substrates and annealed at 425°C showed different orientations. Typical microstructure studies indicated the presence of submicrometer grains of the order of 0.1 μm.

Pb(Zr,Ti)O3 [PZT] fibers–fabrication and properties

Abstract Abstract Fine scale lead zirconate titanate (PZT) and niobium substituted PZT (Nb-PZT) piezoelectric fibers were fabricated from sol-gel processed viscous “sol” using the “spinning” methodology developed for the continuous production of glass fibers. Subsequent drying and firing at above 750°C gave pure perovskite PZT and Nb-PZT fibers of 30 μm in average diameter. Further densification and grain growth were evident for fibers fired at 1250°C. Experimental methods for the determination of dielectric and polarization properties were developed to overcome inherent electric field difficulty relevant to fine scale fibers. The dielectric constant and polarization hysteresis values of the fibers were comparable with that of bulk ceramics. Preliminary single fiber mechanical pull tests indicated that the tensile strength of 30 μm diameter PZT fibers were similar to that of bulk ceramics, being in the ange of 35–55 MPa.

Templated grain growth of textured Sr/sub 2/Nb/sub 2/O/sub 7/

Sr/sub 2/Nb/sub 2/O/sub 7/, a candidate material for high temperature piezoelectric applications, is difficult to pole as a polycrystalline ceramic. To circumvent this problem, a process based on templated grain growth (TGG) for producing textured samples was developed. To accomplish TGG, fine matrix powder, single crystal template particles, and a fabrication technique for orienting template particles in the matrix are required. Single crystal template particles were synthesized by a molten salt technique. The matrix powder was synthesized by solid state reaction of SrCO/sub 3/ and Nb/sub 2/O/sub 5/ in a 2:1 molar ratio. The template particles were dispersed in the matrix powder and tape cast. The initial orientation was induced by the shear field during tape casting and subsequent lamination. Sintering leads to the growth of oriented template particles in the dense matrix, thereby increasing the degree of grain-orientation. The effect of processing parameters and starting powders on the microstructure and texture is presented.

FABRICATION OF SR2NB2O7 THIN FILMS BY SOL-GEL PROCESSING

Sol-gel Sr 2 Nb 2 O 7 thin films were deposited on Si(100) and Pt-coated Si substrates for the first time by spin-coating. The Sr 2 Nb 2 O 7 precursor solution was prepared from strontium metal dissolved in 2-methoxyethanol, acetylacetone, and niobium ethoxide. The formation of phase pure Sr 2 Nb 2 O 7 occurred via an intermediate perovskite phase of composition close to Sr 0.82 NbO 3 . Crack-free Sr 2 Nb 2 O 7 films of ∼0.4 μm thickness were deposited on these substrates using a single-coating followed by heat treatment at 850 °C for 12 h. SEM microstructure and thin film XRD results indicated the deposition of a grain-oriented film on the Pt-coated Si substrate. The room temperature dielectric constant and the loss values of the film measured at 10 kHz are 45 and 0.045, respectively.

Sol-gel thin films of SrTiO3 from chemically modified alkoxide precursors

Abstract SrTiO 3 alkoxide precursor was chemically modified through the addition of chelating agents, diisopropanolamine, triethanol-amine and acetylacetone. The effects of chelation on the crystallization and microstructures of SrTiO 3 sol-gel films on fused silica substrates were studied. Microstructural studies indicated segregation of small crystallites of SrTiO 3 for thin films obtained from triethanolamine and acetylacetone chelated precursor solutions. On the other hand, diisopropanolamine chelated solution yielded dense and smooth films.