The proposed work encompasses the fabrication and characterization of ferroelectric Pb(Sc _0.5 Ta _0.5 )O;i3 (PST) thin films by means of metal-organic chemical vapor deposition (MOCVD) techniques. We will also perform spectral response measurements, frequency response measurements, blackbody responsivity measurements, and noise measurements. The performance of the PST detectors will then be compared with commercial state-of-the-art pyroelectric detectors. The ultimate goal of this work is to develop a room-temperature infrared radiation detector. The proposed IR detector development is based upon a different class of materials, the ferroelectric PST system, and a novel detection approach which utilizes both the ferroelectric and the pyroelectric properties of PST.

Lead titanate (PT) and lead zirconate titanate (PZT) are perovskite-type ferroelectric materials having useful ferroelectric piezoelectric and pyroelectric properties. These materials are very useful for applications in pyroelectric sensors, infrared detectors, piezoelectric transducers, and nonvolatile memory chips. The goal of this research is to employ the MOCVD method to fabricate epitaxial and polycrystalline PT and PZT thin films on various kinds of substrates. Growth parameters and structures of the films were found to be highly dependent on the substrate materials. Knowledge of the domain formation and the preferred orientation of the thin film is the central theme of this research.

The primary objective of this research is to produce oxide thin films for sensor applications. One is a flammable gas sensor using SnO;i2 and the other is a heavy-metal detection sensor in drinking water using Pb-Ag oxide. These oxide thin films are grown by the MOCVD technique. Microstructural analysis is also carried out on the grown films using XRD, SEM, TEM, AES, and XPS. Sensing tests are done for SnO;i2 using resistivity measurements with reducing gases such as H;i2, alcohol, etc. Whereas for heavy-metal sensors, tests are done using electrolyte methods in collaboration with Motorola. Models are suggested to explain the measured sensing properties.

Solid-state nonlinear optic and electrooptic devices offer many advantages, including speed, compactness, simplicity, and reliability. Ferroelectric crystals show the strongest nonlinear properties and have high optical damage thresholds. The research is directed at the growth of high-quality single crystals of Sr _x Ba _1-x Nb;i2O;i6 and BaTiO;i3. Mechanisms of crystal growth are determined. Methods to control the ferroelectric domains are developed. Electrical and optical properties are investigated using structure-property and processing-property relationships for nonlinear optical and electrooptic ceramics. Understanding of the role of dopants is pursued with regard to holographic storage, laser host, and ferroelectric switching applications.

Lead zirconate titanate (PZT) perovskite materials are of considerable technological importance, particularly with regard to physical properties such as pyro- and piezoelectricity and electric field-induced antiferroelectric-to-ferroelectric phase switching. A systematic study of the effects of temperature, Sn- and La-substituents, and Zr/Ti ratio on the evolution of incommensurate phases in high Zr-content PZT is carried out by hot- and cold-stage TEM. Particular attention is paid to the possible development of 1/x[1 incommensurate modulations and to the resul- tant influence on the macroscopic properties. The pur- pose of this investigation is to obtain a fundamental under- standing of microstructure-property relationships for electroceramics.

Rare earth manganese perovskites doped with divalent cations, such as Ca, Sr, Ba, and Pb, have been shown to exhibit greatly enhanced magnetoresistive properties when compared with metallic heterolayers. Improved magnetoresistive behavior is greatly desired for sensor applications, such as magnetic read heads, or advanced computer memories, such as MRAM cells. Current research is concerned with the electronic behavior and morphological characterization of doped rare earth manganese perovskite single crystals. Resulting candidate materials were deposited by low-temperature solution processing and self-assembled patterning to form integtated structures for devices.

Sol-gel-derived PZT thin layers deposited on silicon were examined for their shrinkage behavior using in situ ellipsometry. Correlating densification data with thermal analysis (DTA, TGA), the effect of pyrolysis and crystallization on layer shrinkage is observed as experimental parameters such as water of hydrolysis, heating rate, and layer thickness are systematically varied. The resulting stresses in the coating are measured as a function of heat treatment by a laser reflectance technique and related to associated densification phenomena and substrate/layer thermal expansion mismatch.

Thin films of manganese perovskite oxides exhibiting a giant magnetoresistance (GMR) effect attract great interest for magnetic sensor technology with high resolution capability. GMR thin films were deposited by spin-casting of alcoholic precursor solutions. The GMR ratios for various manganese oxide, La(Ca,Pb)-Mn-O systems were determined by SQUID and transport measurements and related to the processing conditions. Research underway is investigating the relationship between chemical processing, microstructure development, and physical properties.

Thin-layer ceramics have diverse applications as integrated capacitors, sensors, display components, and other devices. Solution processing allows deposition of such layers at greatly reduced temperatures on metal, oxide, and semiconducting substrates with control of stoichiometry, doping level, and crystalline order. Current research is directed at a new selective deposition technique made possible by functionalization of substrates with self-assembled layers. Derivitization of metal, oxide, and semi- conductor substrates with hydrophilic or hydrophobic assembled layers enables preferential wetting of surfaces by solution or vapor deposition techniques. Lithography-free selective deposition of ceramic thin layers has been demonstrated.

Conductive oxide LaNiO;i3 (LNO) electrodes and ferro electric PZT thin films were integrated by sol-gel processing. By changing the electrode combination of Pt and LNO, four integrated capacitor structures were prepared: Pt/PZT/Pt/Si, Pt/LNO/PZT/Pt/Si, Pt/LNO/PZT/Pt/Si, and Pt/PZT/LNO/Pt/Si. Ferroelectric properties and fatigue behavior were investigated. Structural and morphological features and electrical properties were determined for LNO films deposited on single-crystal substrates, SrTiO;i3(100), LaAlO;i3(100), sapphire(0001), and fused quartz by XRD, AFM, SEM, and TEM.

Recently, bismuth-layered compounds, such as SrBi;i2Ta;i2O;i9 and SrBi;i2Nb;i2O;i9, have been recognized as potential candidates for nonvolatile ferroelectric memory applications. However, their basic structures and intrinsic properties are not well understood. This research is directed at the growth of sizable single crystrals of SrBi;i2Ta;i2O;i9, SrBi;i2Nb;i2O;i9 materials. Several crystal growth techniques, such as Czochralski, top-seeded solution growth, and hydrothermal, are under investigation. Their structures and ferroelectric and optical properties will be determined.

SrBi;i2Ta;i2O;i9 (SBT) is a bismuth-layered ferroelectric compound. It is of interest for applications in capacitors and nonvolatile ferroelectric memory elements. This research is directed at the preparation of SBT thin films by chemical methods. Microstructure development for different synthesis conditions, microstructure-property relationships, and ferroelectric fatigue mechanisms are under investigation. SBT thin-film capacitors and their integration with silicon are under study.

The complex piezoelectric properties of lead zirconate titanate based ceramics are being studied. Investigations are being performed using a modified Michelson-Morely interferometer, which can measure both the real and phase components of the response as a function of temperature and frequency. Investigations are being performed for various ac drive amplitudes and dc bias levels. It is anticipated that these studies will lead to a more comprehensive understanding of the fundamental electromechanical coupling mechanism in ferroelectrics.

The microstructure property relationships in various ferroelectric and piezoelectric ceramics are being studied by transmission electron microscopy. Investigations of the phase transformational characteristics are being performed in situ by hot- and cold-stage methods. Corresponding bulk property investigations are also being performed. Compositional systems currently being investigated include lead zirconate titanate (PZT), La-modified PZT, lead magnesium niobate, strontium barium niobate, and Sn-modified PZT. It is anticipated that these studies may lead to a more comprehensive understanding of the influence of impurities on ferroelectric and antiferroelectric domain structures and phase transformational characteristics.

The dielectric, piezoelectric, and electrically induced strain and polarization characteristics of antiferroelectric Sn-modified lead zirconate titanate ceramics are currently being investigated. Corresponding transmission electron microscopy studies are also being performed. These investigations are revealing the nature of the complex structure property relationships in these materials for the first time. An unusual incommensurately modulated polar structure has been observed. Changes in the modulated structure are being correlated with changes in the macroscopic response characteristics. Evidence is indicating that the nonlinear response is controlled by the modulation of the incommensurate structure by an applied electrical field.

The dependence of the dielectric response characteristics of ferroelectric, soft ferroelectric, and relaxor ferroelectric materials is being studied as a function of ac drive amplitude. Investigations are being performed as a function of temperature, frequency, and superimposed dc bias. These investigations have already revealed the presence of strong nonlinearities in critical compositional regions. The mechanisms underlying the anomalous nonlinearities are currently being studied and related to microstructural changes by transmission electron microscopy.

Studies of lead magnesium niobate lead titanate crystalline solutions are being studied for the purpose of achieving enhanced electrically induced strains and electromechanical coupling coefficients. Compositional modifications are being investigated that lead to improved performance coefficients with reduced hysteresis. Studies are being performed by dielectric spectroscopy, piezoelectric spectroscopy, and electrically induced strain and polarization methods. It is hoped that the investigations will lead to the development of the next generation of high-performance transducer/projector materials for underwater acoustical imaging applications in lateral waters.

Barium titanate is one of the most important ferroelectric materials. The interrelationships between the structure and properties in this material are being studied by changing the La and Sn contents. These investigations are being performed by dielectric spectroscopy and transmission electron microscopy, with particular attention being paid to the influence of impurities on the phase transformational characteristics and domain structure. The purpose of this study is to develop new lead-free relaxor-like ferroelectric materials for electrostrictive applications.

Minor amounts of CaO and SiO;i2 are being added to MnFe;i2O;i4 to study their effects on the electrical transport properties of the ferrite. The additives are concentrated in the grain boundaries, which is believed to produce high-resistance grain boundaries, surrounding more conductive grains, thus reducing eddy current losses at high frequencies in the ferrite. It is also found that the concentration of dopant in the grain boundary prevents decomposition of the ferrite in oxidizing atmospheres, thus maintaining the stoichiometry of the high-resistance ferrite. Impedance spectroscopy, thermogravimetry, and electrochemical cell measurements are being used in the study.