Elliott B. Slamovich

Domain texture distributions in tetragonal lead zirconate titanate by x-ray and neutron diffraction

The domain structure of ferroelectric ceramics can be altered by the process of electrical poling. This paper develops quantitative approaches for reflection geometry and spherical harmonic texture analysis, both of which describe these changes at angles parallel to and tilted from the poling axis. The x-ray-diffraction approach uses the relative intensity ratio of ferroelectric poles in poled and unpoled lead zirconate titanate to calculate a domain switching fraction (η) or a multiple of a random distribution, which are shown to be linearly related. An x-ray area detector diffractometer was used for these measurements, although the technique applies to any x-ray reflection geometry. The neutron-diffraction approach employs a Rietveld refinement with a spherical harmonic texture model. Both approaches calculate similar domain textures for two poling fields and the small differences between the approaches can be attributed to surface domain texture. This paper shows that the March–Dollase pole distributio...

Increased osteoblast functions on nanophase titania dispersed in poly-lactic-co-glycolic acid composites

The design of nanophase titania/poly-lactic-co-glycolic acid (PLGA) composites offers an exciting approach to combine the advantages of a degradable polymer with nano-size ceramic grains to optimize physical and biological properties for bone regeneration. Importantly, nanophase titania mimics the size scale of constituent components of bone since it is a nanostructured composite composed of nanometre dimensioned hydroxyapatite well dispersed in a mostly collagen matrix. For these reasons, the objective of the present in vitro study was to investigate osteoblast (bone-forming cell) adhesion and long-term functions on nanophase titania/PLGA composites. Since nanophase titania tended to significantly agglomerate when added to polymers, different sonication output powers were applied in this study to improve titania dispersion. Results demonstrated that the dispersion of titania in PLGA was enhanced by increasing the intensity of sonication and that greater osteoblast adhesion correlated with improved nanophase titania dispersion in PLGA. Moreover, results correlated better osteoblast long-term functions, such as alkaline phosphatase activity and calcium-containing mineral deposition, on nanophase titania/PLGA composites compared to plain PLGA. In fact, the greatest collagen production by osteoblasts occurred when cultured on nanophase titania sonicated in PLGA at the highest powers. In this manner, the present study demonstrates that PLGA composites with well dispersed nanophase titania can enhance osteoblast functions necessary for improved bone tissue engineering applications.

Critical evaluation of the Lotgering degree of orientation texture indicator

Preferred orientation in textured ceramics is often assessed by comparing the relative intensities of x-ray diffraction reflections to those of a randomly oriented ceramic using the Lotgering degree of orientation ( f ). However, this paper provides evidence that indiscriminate assessments of f can be misleading. Using measured intensities of a modestly textured tape cast bismuth titanate (Na 0.5 Bi 4.5 Ti 4 O 15 ) ceramic, calculated f values vary from 7.4 to 73.2% depending on the reflections included in the calculation. The texture is also quantified by calculating the orientation distribution function (ODF) using measured pole figures. A model is then presented that demonstrates f is nonlinear with the multiple of preferred (00 l )-orientations, the standard unit of the 00 l pole figure.

Porous Polymer/Ceramic Composites for Luminescence-Based Temperature and Pressure Measurement

Porous Polymer/ceramic films were processed via tape casting. Upon doping with luminescent molecules such as platinum(II) octaethylporphine and [Ru(4,7-diphenyl-1,10-phenanthroline) 3 ]C1 2 , the films were used as pressure sensors, yielding a Stern-Volmer constant of A ranging from 0.02 to 0.61. These films also exhibited very fast response times (∼I ms). Tape cast films doped with Rhodamine B were used as temperature sensors under cryogenic conditions. The temperature sensitivity of the doped films increased with increasing Rhodamine B concentration.

Domain switching anisotropy in textured bismuth titanate ceramics

In a poled ferroelectric ceramic, the probability of crystallographic poles oriented in any given specimen direction is the multiple of both the initial crystallographic texture and the domain switching fraction. In this paper, the non-180° domain switching fraction is shown to be dependent on the initial crystallographic texture and poling direction in tape cast Na0.5Bi4.5Ti4O15 ceramics. The domain switching fraction is 0.18 out of a maximum of 0.50 when poled in a direction in which most of the possible ferroelastic structural distortions are oriented (tape casting plane) whereas no non-180° domain switching is discernable when poled in a less-preferred direction. The mechanism for domain switching anisotropy in textured bismuth titanate ceramics is suggested to be the synergistic alignment of ferroelastic structural distortions, analogous to the mechanical clamping conditions in poling ferroelastic thin films.

Hydrothermal processing of BaTiO{sub 3}/polymer films

Hydrothermally derived films of BaTiCO 3 were fabricated by reacting thin layers of titanium organometallic liquid precursors in aqueous solutions containing Ba(OH) 2 and having a high pH. Cubic submicron polycrystalline films of BaTiCO 3 (thickness = 1 μm) were formed at 70°C. Low concentrations of block copolymers of polybutadiene and polystyrene were incorporated into the liquid precursor to prevent precursor film cracking. Higher polymer concentrations allowed fabrication of polymer/ceramic composite films by virtue of the low temperature used in hydrothermal processing.

Texture and Symmetry Relationships in Piezoelectric Materials

The anisotropy that is inherent to piezoelectricity is directly tied to the symmetry of domains within the crystals of polycrystalline piezoelectrics. Alloy design for these oxide materials is often focused on influencing pinning of domain walls in polycrystals that have been subjected to high fields and elevated temperatures to introduce the ‘poled’ condition from which most piezoelectric devices operate. We have investigated a wide range of these oxides consisting of single phases or mixtures of phases that may be all or partially piezoelectric in character. Crystal symmetries investigated include tetragonal, orthorhombic, rhombohedral and monoclinic with some phase transitions evolving during high-temperature processing or during poling. Materials investigated include a range of bismuth titanates, lead titanates, lead zirconate titanates and sodium niobates. A variety of texture evaluation techniques, including area detector x-ray diffraction, synchrotron x-ray sources, and neutron sources have been utilized along with Rietveld diffraction modeling tools to enable a deeper understanding of domain textures, domain texture evolution and synergistic relations between crystallographic textures and domain textures. This paper documents an understanding of texture and anisotropy in these materials, and provides insight on approaches to optimize textures for high performance in these materials and demonstrates how these tools can be used to evaluate processing variations from production of these materials.

Effect of Processing Temperature on the Morphology of Hydrothermally Derived Barium Titanate/polymer Thin Films

Thin-film composites of BaTiO 3 particles in a polymeric matrix were processed by reacting films of a titanium alkoxide, mixed with a polybutadiene-polystyrene triblock copolymer, in aqueous solutions of 1.0 M Ba(OH) 2 at temperatures ranging from 60 to 90 °. After reaction, the composite films displayed distinct surface and subsurface morphologies. The film surface consisted of a continuous layer of BaTiO 3 grains, the film grain size decreasing from 180 to 60 nm as the reaction temperature increased from 60 to 90 °. The subsurface growth of BaTiO 3 depended on the presence of a percolating network of hydrolyzed titanium alkoxide, which enabled the reaction solution to permeate throughout the thin film. The resulting subsurface film morphology was composed of segregated regions of BaTiO 3 particles dispersed throughout the polymeric matrix. The growth of subsurface BaTiO 3 particles appeared to be constrained by the polymer matrix, resulting in a subsurface particle size of approximately 5 to 10 nm that was independent of the hydrothermal processing temperature. The reacted films displayed a dielectric constant ranging from 10 to 15 at room temperature and a frequency of 10 kHz.

Measuring the critical thickness of thin metalorganic precursor films

Successful application of sol-gel, metalorganic decomposition, or hydrothermal routes to ceramic thin films depends on the mechanical integrity of the precursor film. Above a critical thickness, a precursor film will crack or decohere from the substrate during drying. The cracking and thickness of thin metalorganic precursor films were simultaneously observed during drying using a standard optical microscope. Isochromatic color fringes produced by interference of reflected white light were used to monitor film thickness. The critical film thickness was determined by the color fringe corresponding to the thickness at which propagating cracks terminated. As a demonstration of the technique, the critical thickness of titanium di(isopropoxide) bis(ethyl acetoacetate) films was measured, showing increased critical thickness with the addition of small amounts of an elastomeric polymer.

Product and Component Grain and Domain Textures in Ferroelectric Ceramics

Ferroelectric/ferroelastic structures exhibit systematic crystallographic distortions below certain phase transition temperatures. Domains, or regions of spatial continuity in such distortions, form in a self-compensating pattern when cooled in the absence of an applied field, forming equal volume fractions of all possible states by uniform selection of crystallographic variants. An applied field (poling) can alter the volume fraction of domains within the ferroelectric phase by switching of the non-preferred orientations, a form of ferroelectric domain texture. When ceramics possess a crystallographic texture prior to inducing domain texture, the two component textures combine multiplicatively to form the complete product texture. Using tape cast bismuth titanate (Na0.5Bi4.5Ti4O15) with an initial crystallographic texture, this paper establishes the quantitative approach for resolving both the component grain and domain textures and describing the complete product texture.