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Bismuth titanate (Bi4Ti3O12), a member of the layered perovskite family, has a unique set of ferroelectric properties, which include a high remanent polarization, low coercive field, and high Curie temperature, that make it a possible candidate for data storage applications. For this investigation, bismuth titanate, or BiT, films were fabricated via sol-gel method to examine the effect of processing on phase development and orientation. Solutions were deposited onto platinized silicon, and then heat treated for one hour at temperatures ranging from 550°C to 700°C in 100% O2. It was found that c-axis orientated BiT films could be formed at temperatures as low as 550°C by using bismuth oxide template layers, while films without bismuth oxide templating possessed a random orientation over the same temperature range.

The influence of the intercalate species on the quasi-static electrochromic behavior of tungsten-oxide-based devices is investigated. Two different electrolytes are used in the devices: an aqueous sulfuric acid solution, from which it is assumed that intercalation of hydrogen occurs; and a solution of lithium perchlorate in propylene carbonate, from which it is assumed that intercalation of lithium occurs. Experiments are performed in which a step-current of small magnitude is imposed through the device, and the corresponding time-dependence of the electrical potential and optical transmission are measured simultaneously. The behavior of the optical efficiency is relatively insensitive to the nature of the intercalate species, but the device potential is appreciably more sensitive to lithium intercalation than to hydrogen intercalation. The disparity in electrical behavior is likely due to increased strain effects and/or a diminished availability of sites associated with the larger lithium intercalate. It is shown that the electrical and optical behavior of the two types of devices may be related by a single linear scaling relation, indicating that the fundamental processes involved in the operation of the devices are similar.

An analytical description of devitrification kinetics induced by time-dependent nucleation and growth of crystallites during a quench-heating cycle is proposed. Relevant experimental situations include differential thermal analysis (DTA) or differential scanning calorimetry (DSC). The proposed description involves very few assumptions regarding the temperature dependence of various kinetic parameters, but rather employs measured values of growth rates. It is shown that the conventional description of nucleation based on the steady-state approximation, as a rule, is inapplicable for the description of the DTA/DSC experiment for experimentally reasonable quench/heating rates. The latter is confirmed by the analysis of available experimental data on o-terphenyl and lithium disilicate.

A set of phenomenological analysis tools have been developed for the characterization of the optoelectrochemical behavior of electrochromic intercalation devices. Both step current and step potential excitations are considered. Great simplification is afforded by working with the passed charge as the primary independent variable; consideration is also given, however, to the transmission or built-in device potential as independent variables. It is shown that quasi-static intercalation efficiency curves, generated from step current measurements, can elucidate the intercalation site-energy distribution; these curves are also compared to dynamic intercalation efficiency curves obtained from step potential measurements. Quasi-static and dynamic optical efficiencies are also considered and compared. The scaling properties of some of the phenomenological parameters may be used to generate master curves which unify sets of data obtained under a variety of conditions (applied voltages, imposed currents, film thicknesses, etc.). Quantitative predictions can be made of device behavior under conditions not probed experimentally.

Pyroelectric thin films are receiving increasing attention for the next generation of integrated room temperature uncooled IR arrays. Pixel size and NETD (net equivalent temperature difference) of 50 μm and 0.005K are projected respectively. In this study, the 1-D transient response of a pixel consisting of black absorber, pyroelectric, Pt, TiO2, SiO2 and Si are performed. Thermal conduction and radiative transfer are assumed to take place across this stack and at the Si substrate-air interface, respectively. The effects of individual film thickness, IR chopping frequency, thermal conductivity of the thermal barrier layer and substrate thickness on the pyroelectric response are investigated.

Pyroelectric thin films are receiving increasing attention for the next generation of integrated room temperature uncooled IR arrays. In this study, steady state modeling of a pixel consisting of black absorber, pyroelectric, Pt, TiO2, SiO2 and Si are performed. Thermal conduction and radiative transfer are assumed to take place across this stack and at the Si substrateair interface respectively. The effects of individual film thickness, IR chopping frequency, thermal conductivity of the thermal barrier layer and substrate thickness on pyroelectric responsivity are evaluated. At low chopping frequencies, large thermal isolation is crucial to obtain optimal pyroelectric responsivity but at high frequencies, the pyroelectric response is independent of thermal isolation. Large responsivities are also obtained by using thin Si substrates. The modeling also considers air bridge structures, typically used in microelectromechanical devices.

Several silylated coumarin dyes with different linkages and degrees of functionality have been synthesized and incorporated in both SiO2 xerogels and various solvent hosts. The absorption and fluorescence spectra were examined to explore selected structural and environmental effects on the optical properties of these dyes. Silylated dyes (also referred to as grafted or functionalized dyes) are dye molecules that have been chemically altered to provide alkoxysilane functionality allowing the active molecule to be covalently bonded to the host. Silylation of dye molecules had little effect on the absorption and fluorescence spectra in neutral solvent environments. The optical spectra of silylated dyes compared to those of their conventional counterpart were less influenced by the local chemical environment (e.g., pH) and thus allow for greater control and stability of the fluorescent properties of the dyes in different host environments. Spectroscopy during the drying/gelling of a derCoum xerogel film conta...

The photostability characteristics of numerous silylated coumarin dyes within SiO2 xerogels and SiO2:PDMS Polyceram films, and of neat silylated coumarin dye films have been determined and related to the sol−gel processing conditions and host composition. FTIR spectroscopy was used to monitor the hydrolysis reaction rates of the silylated dyes and other Si−alkoxide precursors. The silylated dyes had varying reaction rates depending on the degree of functionality and the linkage between the alkoxide and the dye. Matching the reaction rates between TMOS and the silylated dye was accomplished by prehydrolysis of the silylated dye. The photostability of the dyes in the xerogels was measured by monitoring the drop in fluorescence intensity upon pumping with a N2 laser and also by monitoring the drop in dye absorption upon irradiating the films with a UV lamp. At optimized prehydrolysis times, a silylated coumarin dye (derCoum) within a SiO2 xerogel host demonstrated a 3-fold improvement in long-term photostabi...

We consider nucleation of crystalline phase in a glass-forming melt which is quenched at some arbitrary rate, S, and then reheated at some other (typically smaller) rate, H. In conventional (steady-state) approaches it is assumed that the nucleation rate is a function of temperature only, so that the number of nucleated crystallites is proportional to 1/S+1/H. We demonstrate, however, that in general the nucleation rate depends on the quench/heating rate and that there exists an S- and H-dependent temperature region which effectively does not contribute to nucleation, so that the aforementioned scaling does not hold. An expression for the non-steady-state nucleation rate is derived analytically. In certain cases, the number of nucleated crystallites can be reduced by orders of magnitude compared to the steady-state predictions. The results are tested against numerically exact data obtained from the Turnbull–Fisher nucleation model.

Transparent, durable films of lithium diborate gel can easily be prepared on a variety of substrates from supersaturated aqueous solutions of lithium hydroxide monohydrate and boric acid by spin-coating. The gel to dried gel to glass to crystalline lithium tetraborate (Li2B4O7) transformation has been studied by infrared spectroscopy of thin films cast on potassium bromide windows. Examination by scanning electron microscopy disclosed that distinctly different crystal morphology was associated with a difference in the transformation rate observed between gel and dried gel films. Films of 250 nm to 30 μm in thickness have been produced.

Sol-gel derived Y2O3 thin films have been prepared on platinum coated silicon wafers and fired to temperatures ranging from 400°C to 750°C. Multiple coats were used to obtain films up to 0.5 μm thick with an intermediate firing of 400°C between coatings. Top Pt electrodes were sputtered to form monolithic capacitors. These films exhibited a dielectric constant of 18 and a leakage current of 10−11–10−7 A/cm2, making them attractive candidates for high dielectric constant dielectric films in high density DRAMs.

In conventional descriptions of nucleation and crystallization kinetics, it is usually assumed that the kinetic parameters related to the viscosity of the melt depend exclusively on the current temperature of the system. On the other hand, after a rapid quench to a low temperature, T, the viscosity, η, requires a time (τη) to reach its equilibrium value, η∞(T). Since the transient viscosity, η(t), can be much smaller than η∞ and isothermal crystallization kinetics are inversely proportional to the fourth power of the viscosity, a substantial increase in the crystallized volume fraction can be anticipated compared to what is predicted using η∞. An analytical study of this effect is presented, together with estimations of experimental observability. Typically, the latter is associated with temperatures below the glass transformation region.

There has been considerable interest in ferroelectric (FE) films especially for non-volatile memories and ultra high density DRAM applications. Such FE films typically consist of lead zirconate titanate (PZT) with novel oxide contacts, or layered perovskite such as Sr2Bi2TaO9. Recently, there have been reports of sputtered YMnO3 films which exhibit a single polarization axis and do not contain any volatile species of Pb or Bi. Single crystal YMnO3 exhibits satisfactory polarization (6 μC/cm2) and low coercive field (

The unique sol/gel behavior of an organic/inorganic hybrid material synthesized from 3-aminopropyl-triethoxysilane (3AS) and tetramethoxysilane (TMOS) is discussed and examined. The addition of H2O to a mixture of a basic (3AS) and an acidic (TMOS) alkoxide leads to rapid gel formation. This wet gel reverses to a sol upon heating which is attributed to the dissolution of siloxane bonds between the surfaces of colloidal particles in the gel. The reversed sol dries to an optically transparent solid which is water soluble. The water solubility and the stability of these colloidal particles are described by their aminopropyl/silanol surface and the electrostatic interactions between them using DLVO theory.

Ferroelectric (FE) thin films have been widely studied, especially for their electrical and ferroelectric properties, such as nonvolatile FE memory and ultrahigh density DRAMs. FE films also give rise to a variety of interesting and unique optical applications, such as electro-optic switches, passive and active waveguides, second harmonic generation, optical data storage, optical diodes and photovoltaic devices. Their dielectric properties have been extensively optimized but the optical and electro-optical aspects have not been satisfactorily explored. This paper will review the latest advances in the optical and electro-optical properties of FE films, highlighted by data obtained from our laboratories. Optical (refractive index and waveguiding loss) and electro-optical (linear (r 33) and quadratic (R 33) electro-optic coefficients) properties will be presented. Optimization of these properties by precise tailoring of chemistry, processing conditions and microstructure is discussed. Low optical l...

This paper addresses the current state and future prospects of sol-gel processing. It summarizes responses to a questionnaire received from more than four dozen leaders of the sol-gel community. Overall, the respondents remain quite sanguine about the future prospects for the field, and with numerous areas where sol-gel processing can provide unique capabilities and novel materials. The present authors acknowledge this potential, but argue that its achievement will depend upon greatly increased involvement of the sol-gel community with applications, and carrying out a much larger fraction of sol-gel research in the context of applications.

There has been a lot of interest on ferroelectric (FE) films especially for non-volatile memories and ultra high density DRAM applications. These films such as PZT and (Ba,Sr)TiO3 are crystalline perovskite. BiFeO3 is an interesting antiferromagnetic material which belongs to the perovskite crystal structure. Sol-gel derived BiFeO3 films have been prepared on platinized Si substrates and their electrical and magnetic properties were obtained. XRD indicated that the films were crystalline perovskite when fired at 400°C and above. Dielectric constant of up to 100 was also obtained; however, the films tend to exhibit low resistivities especially in films fired to higher temperatures. The hysteretic loops obtained indicated a remanent polarization and coercive field of 5.5 μC/cm2 and 180 kV/cm respectively.

Sol—gel processing is a versatile method for depositing oxide based coatings on a variety of substrates in an economical manner. The present review will consider coatings deposited on glass, and will discuss a number of representative applications for such coatings, namely anti-reflection coatings, transparent conducting coatings, anti-static coatings, fluorinated coatings, coatings incorporating active dye molecules and ferroelectric coatings.

Sol-gel derived PLZT, including PbTiO3, PbLaTiO3 28, PLZT 9/65/35 and PZT 53/47 films were prepared on platinized substrates. The dielectric and ferroelectric properties of the films were measured at 260K -580K. The values of polarization, coercive field dielectric constant and dissipation factor in these films typically increased with increasing temperature. The changes in dielectric properties of the films with temperature were not sharp unlike the transitions in single crystals or bulk ceramics. The pyroelectric coefficients, on the other hand, decreased monotonically with increasing temperature in all these films.

ZnO films exhibit a wide range of interesting material properties. Recently, ZnO films have been studied for sensing applications based on their piezoelectric and pyroelectric behaviors. Reported literature values of piezoelectric and pyroelectric coefficients of ZnO films are in the range of 11–12 pm/V and 1.0–1.4 nC/cm2-K Respectively. In this study, the piezoelectric properties of sol-gel derived ZnO thin films were measured. These films were prepared on platinized Si wafers and fired to temperatures ranging from 550°C to 750°C. Multiple spincoating was performed with an intermediate firing at 400°C between coatings to obtain films up to 6000 A thick. Top Pt electrodes were sputtered to form monolithic capacitors. XRD indicated that the films consisted of crystalline wurtzite at firing temperature as low as 400°C, and that the c-axis orientation increased with increasing firing temperature. A dielectric constant of 10 was obtained, while piezoelectric characterization indicated d33 values as l...

High-quality thin film dielectric materials are critical for the next generation of integrated microwave devices. Much recent attention has been focused on ZrTiO4 and Sn doped ZrTiO4 films for applications in these devices. Sol-gel derived Sn doped ZrTiO4 thin films were prepared on Si and platinized Si wafers and fired to temperatures ranging from 550°C to 700°C. Multiple spincoating was performed to obtain films up to 0.5μm thick, with intermediate firings at 400°C between coatings. The ZrTiO4 films exhibited a dielectric constant of about 32 with low leakage currents of 2×10−9 A. These films were crystalline when fired to 700°C or above. The addition of Sn lowered the dielectric constant but also improved the dissipation factor.

There has been a lot of attention on novel oxide electrodes, e. g., RuO2, LaSrCoO3, YBCO, for contacts to ferroelectric capacitors. Such devices were reported to yield fatigue-free behaviors which are crucial for implementation in ferroelectric memory technology. Typical Pt/PZT/Pt capacitors fatigue as fast as after 104 cycles. In this study, sol-gel techniques are used to prepare both conducting RuO2 and PZT 53/47 thin films. Conductivity of the RuO2 films ranged was measured as 5 × 10−4 Ω-cm. Oxidized Si and platinized Si wafers were used as the substrates; Si/ SiO2/RuO2/PZT/RuO2 and Si/SiO2/Pt/RuO2/PZT/RuO2/Pt and Si/SiO2/Pt/PZT/Pt capacitors were obtained. The effect of RuO2 electrode on microstructure, ferroelectric properties and leakage characteristics will be discussed.

Pyroelectric IR imaging, especially based on monolithic technology integrated with semiconductors, is receiving increased attention for the next generation of room temperature uncooled IR cameras. In the present work, sol-gel derived PZT, including PbTiO3, PLT 28, PLZT 9/65/35, and PZT 53/47, films were prepared on platinized Si substrates. Their pyroelectric properties were determined, and are discussed with respect to film microstructures, processing, and chemistries. Pyroelectric coefficients as large as 7.7×10−8 C/cm2-K, were obtained for PZT 53/47 films.

General methods for the analysis of step-current measurements on intercalation devices are applied to an aqueous, protonic, tungsten oxide-based device. Plots of the built-in potential as a function of the passed charge, V{sub bi}({Delta}Q), are generated. Methods are demonstrated for extracting a useful indicator of the intercalation level from {Delta}Q and for relating V{sub bi} to the applied potential. An intercalation efficiency, {zeta}, is defined, and {zeta}(V{sub bi}) plots are generated. With proper accounting for extraneous contributions, {zeta}(V{sub bi}) provides a measure of the effective site energy distribution and of the instantaneous efficiency (or capacity) of the intercalation process. A nonfaradaic spontaneous deintercalation process has been observed which acts to deintercalate the film without contributing to the measured current. Methods for including this effect in the analysis are presented in terms of a virtual current.

Sol-gel derived PZT thin films were spincoated on Corning 7059 glass substrates and fired to temperatures ranging from 500C to 600C for 30 min. The PZT compositions consisted of PZT x/y where x/y = 0/100, 20/80, 35/65, 53/47, 65/35, 80/20 and 100/0. Only single coated films were used since multiple coatings led to higher losses. XRD was used to characterize the phase assembly of the fired films and indicated that films with higher Zr contents contained proportionally more pyrochlore; while films with higher Ti contents have higher perovskite contents. UV-VIS spectroscopy was utilized to obtain the transmission and optical properties(refractive index and extinction coefficient) via the envelope method. Waveguide losses were measured using prism coupling at the 633 nm HeNe laser wavelength. The waveguide losses in the PZT films ranged from 1.3 to 2.0 dB/cm. The surface texture or morphology of the films significantly affected the optical losses as striated films gave losses of 2.7 to 3.3 dB/cm. The...

Numerous silylated coumarin dyes have been incorporated within silica : polydimethylsiloxane Polyceram hosts using the sol-gel process to form crack-free, polishable monoliths. The use of silylated laser dyes allows for covalently bonding the laser dyes to their hosts. Photostability of the samples was evaluated by measuring the decrease in the dye absorption in the Polyceram upon ultraviolet lamp exposure and by monitoring the fluorescence intensity as function of pump pulses from a N2 laser at 337 nm. Both methods showed a significant improvement in photo- and thermal-stability of the silylated dye Polyceram compared to that of the unsilylated dye Polyceram at a dye : Si mole ratio of 10-4 : 1. The improved stability is attributed to the immobilization and higher degree of caging of the silylated dye Polyceram with respect to the unsilylated dye Polyceram.

Polyceram materials are attractive hosts for laser dyes because they can have high optical transparencies, high laser damage thresholds, and the ability to tailor optical properties by varying the composition and synthetic routes. Pyrromethene 567 has been successfully incorporated within silica: polydimethylsiloxane (PDMS) Polycerams to obtain polishable, crack-free, transparent monoliths using the sol-gel process. Fluorescence photostability was measured by pumping with aQ-switched, frequency doubled Nd: YAG laser (532 nm) at a pulse rate of 10 Hz. Fluorescence intensity dropped to 50% after approximately 50,000 pulses at a fluence of 0.10 J/cm2. UV degradation studies were performed on Polycerams with different polymer contents, and the absorption photostability is related to the solubility and type of caging of the dye.

The PbO content of lead zirconate titanate(PZT) films has been widely recognized as affecting not only the phase assembly and microstructure but also the dielectric and ferroelectric properties. Excess PbO has often been incorporated in PbO-based films to optimize the film properties by compensating for PbO loss either through volatilization or diffusion into the substrates. Sol-gel derived PZT 53/47 films with various PbO contents, i.e., Pbx Zr0.53 Ti0.47O3 (x = 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.05, 1.10, 1.25 and 1.5) were prepared on platinized Si wafers and fired to temperatures ranging from 550C to 700C under oxygen. Multiple spincoating with an intermediate firing of 400C between coatings was performed to obtain films up to 0.5μm thick. After the final crystallization firing, top Pt electrodes were sputtered to form monolithic capacitors. These capacitors were subjected to dielectric and ferroelectric characterization using an impedance analyzer and a Radiant Technologies RT66A Ferroelectric ...

Wet chemical processing of ceramics, glasses and inorganic-organic hybrids for optical applications is rapidly developing. The present review focuses on optical films obtained by wet chemical processing, with emphasis on recent developments in ferroelectric and magneto-optic films, rare earth lasers and surface patterned films. Where appropriate, the subject matter is illustrated with recent results from our laboratories.

Ferroelectric(FE) films exhibit interesting electro-optic (EO) properties and are utilized in devices used for second harmonic generation, spatial light modulators and optical switches. These films typically yield large values of linear and quadratic electro-optic coefficients. Solgel derived FE films namely PZT 53 47 and PLZT 28/0/100 were prepared on conductive glass substrates. 0.5M precursor solutions based on the appropriate stoichiometric amounts of lead acetate, La nitrate and Ti Zr alkoxides were refluxed for 1 hour and later spincoated on the substrates. They were the fired to 600C to crystallize them into single phase perovskite films. Top Au Pd electrodes were deposited to form the top contacts for the capacitors. The refractive indices, extinction coefficients, linear and quadratic coefficients of the films were obtained using multiangle reflection ellipsometry. These parameters were then used to calculate the linear and quadratic electro-optic coefficients of the films. The quadratic EO coefficients of PLZT 28/0/100 and PZT 53 47 films were measured to be 0.07 and 0.38 × 10−16 m2/V2 respectively while the linear electrooptic coefficients of PLZT 28/0/100 and PZT 53 47 were found to be 59 and 315 pm/V respectively, with the reff value for PZT 53 47 the highest among reported ferroelectric films in literature.

A series of solgel derived lead lanthanum titanate films were prepared on Corning 7059 glass substrates. Waveguiding properties of these films were studied as a function of La content and film thickness. 0.5M precursor solutions based on lead acetate, La nitrate and Ti Zr alkoxides were refluxed for 1 hour and later spincoated at various speeds on the substrates under clean room condition. Films were fired to 400C for 1 hr to burn off the organics and to consolidate the coatings. They were then fired at temperatures ranging from 500C to 600C. XRD was used to determine the phase assembly present in these films; the presence of La seemed to aid in the formation of the perovskite phase. Transmission spectra were gathered using a UV-Vis spectrometer; and the spectra were then used to calculate the refractive indices based on the envelope method. The waveguiding properties and optical attenuation were studied via prism coupling using a rutile prism. The optical losses in these films decrease with La content and also in thicker single-coated films. On the other hand, thicker films achieved by multiple coating appeared to exhibit higher losses. Crystalline PLZT 28/0/100 yielded loss of

PbTiO3-based ferroelectric films are attractive materials for passive and active waveguides due to their high refractive indices (> 2·0), small attenuation losses (1–6 dB/cm) and low processing temperatures (< 600C). A series of sol-gel derived La-doped PbTiO3 waveguides was prepared on Corning 7059 glasses. 0·5M precursor solutions of Pb1−x/100Lax/100Ti1−x/400O3 with × = 0, 5, 10, 15, 20, 25, 28, 30 and 32 were spincoated on the substrates and fired to 400C, 500C and 600C for 30 mins. XRD was used to determine the phase assembly present in the films as a funcion of La stoichiometry and firing temperature. The presence of La seemed to aid in achieving the formation of single-phase perovskite films. Transmission spectra obtained using a UV-Vis spectrometer provided information on band gap energies; and the spectra were used to calculate the refarctive indices and extinction coefficients based on the envelope method. The refractive index decreased and band gap increased with increasing La content i...

Ferroelectric (FE) films constitute an important component of electro-optic devices; such films have been used for second harmonic generation, spatial light modulators and optical switches. FE films typically yield large values of linear and quadratic electro-optic coefficients. Most electric field induced birefringence measurements have been made with transverse electrodes, i. e. with light beam between poled electrodes. In the present study, an Ultimate Ellipsometer was used; a HeNe laser was directed perpendicularly through FE capacitors with applied voltages and the phase change monitored. The layout of this device is discussed in details. Sol-gel derived PZT 53/47 and PLZT 28/0/100 films were prepared on conductive glass substrates. 0·5M precursor solutions based on the stoichiometric amounts of Pb acetate, La nitrate and Ti/Zr alkoxides were refluxed for 1 hour and spincoated on the substrates under clean room conditions. The films were then fired to 550C to crystallize them to single phase...

PZT films, especially PZT 53/47 films, have been intensively explored for a wide range of applications. A broad range of dopants can be incorporated fairly easily into PZT using sol-gel techniques, resulting in compositional tailoring of material properties. One important dopant is La, forming PLZT compositions which have a larger range of dielectric and ferroelectric properties than the PZT materials. To date, PLZT films have received less attention in electrical applications than PZT films in spite of the wider range of film properties achieveable with the former. A series of sol-gel derived PLZT films was prepared on platinized Si wafers. Selected compositions were prepared covering the entire PLZT phase diagram, namely PLZT x/y/z with y/z = 20/80, 53/47 and 65/35 and x = 0, 2, 4, 6, 8, 10 and 12; and × = 7.5 with y/z = 0/100, 20/80, 65/35, 53/47, 35/65, 80/20 and 0/100. The films were spincoated on platinized Si wafers and fired to 650 – 700 C to convert them into single phase perovskite film...

The kinetic processes relevant to up-gradient crystallization are analyzed in detail. Crystallization occurs upon moving an amorphous sample up through a temperature gradient which is the reverse of traditional crystallization from the melt. Both nucleation and growth processes are important to the present technique. To obtain a highly oriented microstructure, bulk nucleation must be prevented. Generally, a liquid with small nucleation rate and large crystal growth rate is favorable for the present route. The model was tested for the lithium diborate glass system, which yielded a highly oriented microstructure with only isolated additional nucleation events.

Sol-gel techniques have been employed to synthesize a number of organic-modified hybrid materials (polycerams) using a functionalized organic polymer (N-triethoxysilypropyl O-polyethylene oxide urethane) together with a range of metal alkoxides and acetates. Despite the disparate nature of the constituents, the chemistry and processing have been successfully controlled to achieve a high level of homogeneity down to the molecular level. The opticla properties (index of refraction, loss, dispersion and transmittance) of the polycerams are reported as functions of various metal oxides. These properties are then correlated to the homogeneity of the network. Polycerams of differing compositions can be easily designed and synthesized to yield low-loss (

The spreading kinetics of incompletely wetting liquids on porous substrates, highlighting the competition between composite interface spreading and liquid infiltration into the porous substrate are considered. The energetic impact of the surface porosity on the advancing of the contact line is modeled by using three idealized microtopologies associated with the kinetic behavior of the liquid in the pores. The results are used to modify a previously developed hydrodynamic spreading model to include the effects of substrate porosity. The results of a previously developed model for the depletion of a liquid droplet on a porous substrate are then used to consider the interaction between the spreading and depletion processes. It is predicted that, for a wide class of situations, a major portion of the spreading process will generally be completed before liquid drainage becomes significant. A contact angle hysteresis associated with spreading on a porous substrate is predicted to occur, with the advancing angle being larger than the receding angle; and an analogy is made with spreading on a rough or pitted substrate which provides a mechanism for contact angle hysteresis on such surfaces.

A series of sol-gel derived La-doped PbTiO3-containing films was prepared on platinized Si wafers. The compositions investigated include PLT (0-28 mole % La) and PLZT (e.g., 9/65/35 and 12/80/20) films. These films were fired at temperatures ranging from 500 to 750°C. While most of the films were single-phase perovskite when fired at 700°C, lower firing temperatures (∼500°C) are sufficient to obtain crystalline PLT films, especially when the La content is more than 15 mole %. The paraelectric or ferroelectric character of the films as a function of La content is also addressed. In PLZT films, the Zr/Ti ratio affects the crystallization behavior and also the perovskite structure, i.e., either tetragonal or rhombohedral. Ferroelectric PLZT films exhibit high values of both dielectric constant (>700) and leakage current. The values of dielectric constant in the relaxor PLZT films are low, especially when compared to their bulk ceramic values (5000–10000). Paraelectric PLT films exhibit high values o...

A static I-V measurement method for ferroelectric thin films is developed to distinguish the leakage current from the switching current. The initial polarization state and the exponential decay behavior of the switching current are considered in this method. The feasibility of this I-V measurement method is investigated by examining fatigue effects on sol-gel derived PZT thin films. Changes in polarization due to fatigue are correlated with the changes in the switching current and the leakage current.

Recent progress is reviewed on the wet chemical synthesis of films for optical applications. Specific attention is directed to planar waveguides and to electrooptic, non-linear optical and electrochromic films, including recent results obtained in our laboratories.

A series of monolithic Pt-PZT-Pt capacitors was prepared based on sol-gel derived PZT 53/47 films fired to 700 C. After deposition of top Pt electrodes, the capacitors were subjected to post-metallization annealing (PMA) temperatures of 100 C to 700 C. Dielectric and ferroelectric (FE) characterizations were performed. Increasing the PMA temperature produced lower values of spontaneous and remanent polarizations, dielectric constant and leakage currents. The observations are correlated with a proposed FE capacitor model.

Amorphous rumples of Bi 2 Sr 2 Ca 1 Cu 2 O x were produced by quenching from the melt. The early-stage microstructure development in these rumples was monitored using XRD, DTA, and hot-stage TEM. It was observed that the molten glass undergoes phase separation during initial quenching and that subsequent refinement of these features generates the initial DTA exotherm during heating. This exotherm has been found for many related compositions, and has been shown not to correspond to crystallization. This initial phase separation strongly impacts the final microstructure by providing copious nucleation sites for the R-phase that ultimately crystallizes first

Microstructure and phase development of as-quenched and annealed samples of the glass of composition Pb0.32Bi1.68Sr1.75Ca2Cu3Ox have been studied. Evidence for liquid-liquid phase separation during quenching was found The microstructure of this glass during the early stage of crystallization is similar to that found for Bi2Sr2CaCu2Ox (2212) glass. The first phase that crystallizes on annealing at low temperatures appears to be Cu2O. In further heat treatments the sequential crystallization of the R-phase of (PbyBi2−y)Sr2CuOx (‘2201’) composition and the PbyBi2−ySr2CaCu2Ox (‘2212’) phase was found, in agreement with other studies. Phase separation determines the initial crystal phase and the development of the superconducting phases. Phase separation observed in this glass points to the possibility that immiscibility may be a common feature of a wide range of Bi(or PbBi)SrCaCuO compositions.

The behavior of a liquid droplet placed on a porous solid is considered. A model is developed for the infiltration of finitesize liquid droplets into porous materials, including the effects of the instantaneous droplet size on the number of pores in contact with the droplet. Simple analytical solutions are developed for the time dependence of the droplet radius under two limiting case assumptions concerning the kinetic behavior of the droplet as its volume is depleted. The two limiting cases are seen to represent upper and lower limits on the liquid depletion time. Liquid depletion data of silicone liquids on a soda-lime-silicate porous solid are presented and compared with predictions of the models.

General methods for the analysis of step-current measurements on intercalation devices are applied to an aqueous, protonic, tungsten oxide-based device. Plots of the built-in potential as a function of the passed charge, V{sub bi}({Delta}Q), are generated. Methods are demonstrated for extracting a useful indicator of the intercalation level from {Delta}Q and for relating V{sub bi} to the applied potential. An intercalation efficiency, {zeta}, is defined, and {zeta}(V{sub bi}) plots are generated. With proper accounting for extraneous contributions, {zeta}(V{sub bi}) provides a measure of the effective site energy distribution and of the instantaneous efficiency (or capacity) of the intercalation process. A nonfaradaic spontaneous deintercalation process has been observed which acts to deintercalate the film without contributing to the measured current. Methods for including this effect in the analysis are presented in terms of a virtual current.

Sol-gel derived PZT (lead zirconate-titanate) thin films were irradiated to a total-dose of 1 Mrad(Si) or 86 krad(PZT) under open-circuit bias. An asymmetric distortion in the hysteresis curves was observed. The distortion depends on the polarization state of the capacitor before irradiation. Postirradiation electrical cycling makes the hysteresis loops symmetric initially, but results in fatigue effects. The leakage and switching current behavior after irradiation and post-rad cycling were studied using a static current versus voltage measurement. Retention and fatigue properties are not worsened after irradiation except for the polarization reduction. The radiation effects are consistent with the sheet charge model. The fatigue effects due to post-rad cycling are consistent with an increase in the space-charge regions near the electrodes or oxygen-deficient dendrite growth. >

Phase separation is found for the first time in quenched samples of amorphous Bi 2 Sr 2 Ca 1 Cu 2 O x (often called “2212” composition). Clear evidemce for metastable phase separation is found using X-ray diffraction (XRD), transmission electron microscopy (TEM), and differential thermal analysis (DTA). This has serious implications for possible fabrication of high current density devices from these compositions, especially via glass-ceramic processing routes.

Wet chemical (sol-gel) methods have been used to synthesize a variety of ferroelectric (FE) thin films, most notably lead zirconate titanate. Ferroelectric films have a wide variety of applications ranging from non-volatile memory devices to pyroelectric detectors. Recent progress in this area of sol-gel processing is surveyed, and examples are illustrated by results from the authors' laboratory. It is concluded that impressive results have been achieved in the chemical processing of FE films, but that more effective collaboration needs to be established between chemists/ceramists knowledgeable about wet chemical processing, and device technologists knowledgeable about the characteristics of coatings.

Sol-gel-derived lead titanate, lead lanthanum titanate, lead zirconate titanate and lead lanthanum zirconate titanate films were prepared. Second harmonic generation (SHG) activity from these films was explored as a function of composition, processing, phase assemblage, microstructure and orientation. Undoped PbTiO3 films exhibited strong, angular-dependent SHG signals. Incorporation of La and Zr resulted in a decrease in the signal magnitude.