Crystallographic engineering, a concept to utilize crystal anisotropy as well as an engineered domain configuration, resulted in significant enhancement in piezoelectric activity for normal ferroelectric BaTiO₃ crystals. Electromechanical couplings (k₃₃) approximately 85 percent and piezoelectric coefficients (d₃₃) as high as 500 pC/N, higher or comparable to those of lead based ceramics such as PZT and significantly larger than those of tetragonal BaTiO₃ crystals, were detected from crystallographically engineered orthorhombic BaTiO₃ crystals. Orthorhombic BaTiO₃ phase could be stabilized by Zr-doping at room temperature and enhanced electromechanical coupling (k₃₃) approximately 75 percent was detected also by using crystallographic engineering. Macroscopic symmetry was suggested for <001> poled rhombohedral (3m) and orthorhombic (2mm) crystals, based on the engineered domain configuration.

Active Fiber Composites (AFCs) are composed of uniaxially aligned piezoelectric fibers embedded in a polymer matrix. Two interdigital surface electrodes deliver the required driving voltage. A new concept for anisotropic matrix materials in AFCs has been successfully introduced. The matrix material is doped with ferromagnetic, electrically- conductive particles. The particles are locally aligned during AFC manufacturing by magnetic fields and create an electrically-conductive path between the electrodes and the surface of the piezofibers. The new method allows for more flexibility in the design and processing of AFCs and should lead to reduced driving voltages for AFCs. A manufacturing rig for magnetic particles AFCs (mpAFCs) has been designed and fabricated. A materials system has been optimized and processing methods for production of mpAFCs were developed. Several mpAFCs have been successfully manufactured and characterized. Actuation authority of mpAFCs was investigated and compared to standard AFCs.

Lead Zirconate Titanate (PZT) active fibers, from 80 to 250 micrometers in diameter, are produced for the AFOSR/DARPA funded Active Fiber Composites Consortium (AFCC) Program and commercial customers. CeraNova has developed a proprietary ceramics-based technology to produce PZT mono-filaments of the required purity, composition, straightness, and piezoelectric properties for use in active fiber composite structures. CeraNova's process begins with the extrusion of continuous lengths of mono-filament precursor fiber from a plasticized mix of PZT-5A powder. The care that must be taken to avoid mix contamination is described using illustrations form problems experiences with extruder wear and metallic contamination. Corrective actions are described and example microstructures are shown. The consequences of inadequate lead control are also shown. Sintered mono- filament mechanical strength and piezoelectric properties data approach bulk values but the validity of such a benchmark is questioned based on variable correlation with composite performance measures. Comb-like ceramic preform structures are shown that are being developed to minimize process and handling costs while maintaining the required mono-filament straightness necessary for composite fabrication. Lastly, actuation performance data are presented for composite structures fabricated and tested by Continuum Control Corporation. Free strain actuation in excess of 2000 microstrain are observed.

Currently, smart structures utilize both polymeric sensor and PZT-based actuators. Polymeric sensors based upon PVDF are limited to about 70 degrees C operating temperature, while PZT-based actuators are inflexible. This paper examines the use of PZT/polymer composites for smart materials applications. Both ferroelectric (VDF) and non- ferroelectric high temperatuer polymers were studied. High temperature composite sensors were fabricated exhibiting g₃₁ values of 90 X 10^-3 Vm/N compared to 110 X 10^-3 Vm/N for PVDF combined with excellent compliance. On the other hand, 0-3 composite based actuators were fabricated with greatly enhanced d₃₁ over PVDF. Piezo properties and dielectric properties of both sensor and actuators were studied as a function of temperature voltage. Processing-structure-properties relationship was established including key processing parameters such as PZT particle size, enhanced poling additives and polymer properties. Thermal dependence of the 0-3 composites piezoproperties was correlated with glass properties of the polymer. Applications of this new class of 0-3 concepts to cure monitoring of advanced composite systems will be discussed.

THUNDER technology introduces a versatile new family of rugged, robust, reliable piezoelectric actuators and sensors. Because of their pre-stressed composite structure, these powerful yet lightweight devices exhibit unprecedented performance in a durable, solid state package. Both sensors and actuators can be manufactured in a variety of adaptable geometries - squares, rectangles and disks - from several millimeters to many centimeters in size. Wide bandwidth performance can be achieved and maintained even in harsh chemical and temperature environments. Based on an invention patented by NASA, THUNDER is an emerging, enabling technology that holds the promise of significant advancements in numerous 'smart' applications. Development of these applications for smart materials and structures requires extensive characterization of a variety of THUNDER devices in a range of configurations. This comprehensive characterization effort is especially challenging because of the extraordinary flexibility and range of motion demonstrated by THUNDER devices, even under significant load. This paper will discuss important new work in the ongoing program of THUNDER device characterization. The program includes not only development of the characterization process, but also design and manufacture of the test and measurement equipment necessary to conduct meaningful and reliable testing on these unique, high performance devices. Results will be presented on characterization of two configurations of THUNDER devices, including a circular and a rectangular model of different sizes constructed of varying materials. Data will be offered for a number of key performance characteristics, including displacement, block force, plus displacement vs. voltage and displacement vs. force.

The efforts described here are intended to provide a basis for the utilization of novel piezoelectric actuators in smart materials and structures. The actuator design developed in this study is a segmented, piezoelectric tube, with the individual segments driven in a d₁₅ shear mode. The PZT-5A tubes were cut longitudinally in to an even number of equal slender segments. These slender segments were poled individually along their length using a continuous poling technique developed at NRL. The polarization of the poled segments alternates in direction between adjacent segments. The segments were reassembled with a conductive epoxy so that it serves as both joint and electrode. The assembled actuator tubes were evaluated by applying electric field normal to the polarization direction of the segments, demonstrating proof of concept. These solid state prototype devices were driven to precise angular displacement and torque output. Reliability test, including both fatigue and mechanical loading of the device, were conducted. In conjunction with this effort, numerical computation analyses were performed with respect to structural integrity versus segment joint thickness, and the relative effect of cylindrical versus polygonal configurations. These studies facilitated the successful production of prototypes. Projected actuator outputs based on electromechanical test results are also discussed in terms of requirements for noise and vibration control of helicopter rotor blades.

THUNDER is a new generation of piezoelectric actuator/sensors that was developed at NASA Langley Research Center in 1994. THUNDER exhibits large out-of-plane displacement and a very good load carrying capacity relative to other types of piezoelectric actuators. The key factor in superior performance of THUNDER is incorporation of a pre- stressing phase during manufacturing. THUNDER is being produced by commercial manufacturers that have licensed the technology from NASA. THUNDER is a new technology; consequently, there is limited experimental study on its performance. Recently, an extensive set of experiments was conducted at Jamesbury Corporation on THUNDER in order to evaluate its advantages and limitations in active control applications. This paper describes the results of many experiments that were conducted to study the time response, frequency response, hysteresis, creep, and response repeatability of THUNDER.

Multilayer dielectric stack filters have been fabricated using the electrostatic self-assembly (ESA) process to produce quarter wavelength thicknesses of materials with alternating high and low indices. The ESA technique provides significant advantages over other thin-film fabrication methods, including excellent homogeneity for low scattering loss, high thermal and chemical stability, simplicity of fabrication, and low cost. Selection of the molecules in each layer, their orientation at the molecular level, and the order of the layers allow control of bulk optical, electronic, thermal, mechanical and other properties on the nanometer scale. The resulting ability to precisely grade dielectric constant/refractive index through the film thickness makes ESA processing an excellent choice to synthesize multilayer thin-film filters and coatings, including antireflection coatings and reflecting dielectric stacks with spectral width controlled by refractive index and thickness.

Domain wall sin ferroelectric tetragonal poled PZT films have been observed by surface corrugation effects. Boundaries between adjacent 90 degree domains show a vertical shrinkage on the surface as result of coherency defects and shear strain at the interface between domains. The vertical truncation of the surface amounts to 1.0-1.5 nm. The wall thickness of 90 degree domains has been estimated to approximately 1 nm. STM allows to detect domains after metallization of the surface with a Cr-Ni or Ti film. AFM measurements with grounded samples provide a detailed picture of the unmetallized PZT surface. Single crystalline areas consists of strictly oriented domains of 10-15 nm width. Domains show long-range ordering effects due to stress in the film. A mean value of domain width can also be obtained by SAXS and amounts to 17.5 nm. Exertion of stress result into an increase of domain thickness by approximately 1 percent. Electrical switching of single crystallites as well as optical effects have been demonstrated.

Very small-sized ferroelectric domains were induced and observed using a modified atomic force microscopy (AFM). Bias voltage between a conductive AFM tip and a sol-gel processed PZT film caused the switching of small ferroelectric domains. ELectrostatic forces between the polarized area and the tip provide the imaging of the polarized small domains. Applying voltage with the opposite sign can depolarize the polarized area and the formation of a series of data dots was demonstrated. In addition, the retention phenomena of micron size domains in PZT films were investigated. The polarized images disappeared within a few days even without an application of voltage - often called the retention loss or failure. An empirical relationship between relaxation time, bit size and poling time is established and verified. Two operative processes for the retention loss are either the stray charge accumulation on the polarized surfaces or the stress relaxation of the piezoelectric films. An effective way of improving the retention characteristics is suggested. The experimental results obtained in this study provide substantial insight into the mechanism for the retention failure of the polarized domains as well as the polarization behavior in PZT films with a nanometer scale.

The electrostatic self-assembly (ESA) method of creating multifunctional, multi-component thin films layer by layer has proven to yield noncentrosymmetric structures that possess large second order nonlinear responses. The nature of the deposition process results in an alignment of the NLO chromophores that is stable over time, in contrast to poled polymers. ESA nonlinear optical thin films offer the additional major advantages of excellent homogeneity for low scattering loss, high thermal and chemical stability, simplicity of fabrication and low cost. The polar ordering of molecules that occurs due to the inherent nature of the ESA process suggests that a number of NLO thin films may be synthesized using both standard chromophore dyes and molecules specifically designed to yield an enhanced macro- scale net dipole moment. Consequently, we have designed and synthesized several new NLO polymers and fabricated noncentrosymmetric thin-films using the ESA process. These novel polymer films exhibit substantial (chi) (2) values as well as uniform growth and exceptional film ordering.

Different structures of multilayer hard coating thin-films have been fabricated on single crystal silicon and quartz substrates at room temperature by electrostatic self- assembly (ESA) method. This process involves the alternate dipping of oppositely charged polyelectrolytes. The ESA films have shown the formation of highly ordered and homogeneous structures with reduced voids. UV/VIs spectroscopy and ellipsometry were used to observe the ESA deposition process. The hardness and Young's modulus of the films were measured using nanoindentation technique.

Capacitive elements have been formed by depositing multiple layers of selected polymers, inorganic metal oxide nanoclusters, and other molecules between parallel electrically conducting electrode layers of noble metal nanoclusters and thin metal films formed by conventional vacuum deposition methods. Considerations for silica nanocluster dielectric nanoparticles are considered in particular in this paper. Control over the capacitance of the elements was achieved by varying the polymers and inorganic nanoclusters in the dielectric layers, the thickness of the dielectric layer and the 2D area of the elements. Breakdown voltages on the order of tens of megavolts per meter were obtained due to the low defect concentration in the thin film dielectric layers, and the inherent ability of the thin film self-assembly process to avoid molecular impurities and pinholes.

While preventing structural damage caused by dynamic loading is typically addressed at a bridge's structural level, this report presents a design for the internal release of adhesives for resisting dynamic loading of reinforced concrete at the materials level. Normal reinforced concrete lacks the ability to directly respond to the formation of cracking within its own cross section during dynamic loading. Present designs for dynamic loading resistance attempt to control the structure's response by focusing on the properties of mass, stiffness, and damping, as the governing equation for structural response to dynamic loading is modeled.

Magnetorhelogical (MR) elastomers are viscoelastic solids whose mechanical properties are controllable by applied magnetic fields. We have developed a family of MR elastomers, comprising micrometer-sized carbonyl iron particles embedded in natural rubber, that can be processed using conventional rubber-mixing techniques. By crosslinking the elastomer in the presence of an applied magnetic field, field-induced interparticle interactions promote the formation of particle chains and columns aligned along the field direction. The resulting composites possess field- dependent of the mechanical properties of MR elastometers enables the construction of controllable elastomeric components, such as suspension bushings, that may prove advantageous in some automotive applications.

Samples of poly(aniline)-silver-polymer electrolyte particulate composites have been characterized at microwave frequencies when small d.c. electric fields are applied across them in both coaxial line and waveguide measurement test sets. The experimental data shows that the initial conductivity of the materials is dependent on the concentration of sliver metal and suggest that changes in resistance due to chemical switching take place, at least in part, in the manufacture of the composites. When silver is used as the electrodes, the experimental data show that changes in the slope of the cyclic voltammograms coincide with large changes in microwave reflectivity or transmission consistent with increasing conductivity of the composites when fields are applied. The reverse change occurs when the fields are removed. Measurements have shown that the composites are able to switch between the two impedance stats in times of less than one second for well over a million cycles with no apparent depreciation in material properties. Large area films have also been prepared and studied using the 'free space' technique.

Prior interferometric fiber sensors and evanescent wave fiber sensors have proven useful in obtaining information about portions of the lifetime of a composite materials. The overall goal of this research is to develop an IR evanescent wave sensor system that can be used to monitor lifetime of a polymer matrix composite. In this regard, a single fused silica core fiber was placed across a miniature materials tester, while simultaneously having the fiber ends attached to an IR spectrometer. The fiber was strained in increments by the MINIMAT, while the IR spectrometer allowed simultaneous determination of the IR spectrum. An increase in baseline absorbance across the entire IR spectrum occurred as the strain increased. The increase in absorbance is relate to an increase in strain in the fiber. From regression analysis of independent measurements of fiber strain and absorbance, a strong relation between the change in absorbance and change in strain energy was found. Future work will involve incorporation of the strain sensing approach with evanescent wave chemical sensing to allow total lifetime monitoring of polymer matrix composites.

Currently, there are no simple sensing techniques for determining in real-time both the severity and location of structural damage in a composite caused by a dynamic impact event. Materials are known which emit light when they are fractured. This fracture-induced light emissions is known as triboluminescence. A triboluminescent material embedded in, or attached on, a composite structure could act as a real- time damage sensor. The occurrence and severity of the damage is given by the intensity of the resulting triboluminescent light. Since the triboluminescent light emission is fracture-initiated, no signal would be generated by a triboluminescent sensor until damage had actually occurred. Hence no false alarms are generated by this type of sensor. An array of triboluminescent sensors may allow real-time damage location monitoring simply by determining the wavelength of the emitted light. We have developed a series of highly efficient triboluminescent materials with sufficient thermal and chemical properties to allow doping into composites. We report a series of proof-of-principle experiments with these materials which strongly support the potential of triboluminescent sensors to monitor in real- time both the magnitude and location of structural damage.

A new type of actuation device has been conceptualized that meets the needs of both large displacement, force and bandwidth within a package more compact than currently available magnetostrictive and stack-type piezoelectric actuators of similar rating. This concept relies on micro- scale electrohydrodynamic (EHD) pumping of a dielectric liquid within small channels. Configured as an actuator, the EHD pump(s) would be used to move fluid between two reservoirs - each having a compliant membrane that interfaces to the world to provide the means to achieve vibration cancellation or micro actuation.

A laser-assisted process that enables the direct production of electrically conductive structures in the surface of aluminium nitride (AlN)-substrates is presented. The modification of the surface conductivity of AlN is performed by using pulsed excimer laser radiation. The process is systemically examined concerning its dependence on the processing variables. In order to characterize the modification the laser-treated specimens are analyzed with respect to electrical conductivity, chemical composition including factor analysis, X-ray-photoelectron-spectroscopy and electron beam microprobe analysis, structure and morphology.

Large magnetic field induced strain shave been reported in ferromagnetic shape memory alloys. two such alloys, Ni-Mn-Ga and Fe-Ni-Co-Ti are explored. A single crystal of Ni-Mn-Ga is shown to deformed by bending approximately six degrees under the influence of an applied field. This deformation is caused by the motion of a single twin boundary with stable variants of martensite on either side. This effect was demonstrated using either divergent or homogeneous field. Fe-Ni-Co-Ti is a shape memory steel with high saturation magnetization being developed as a magnetic shape memory material. Material properties in this alloy can be controlled by composition and heat treatment and the effects of both are explored. Variation of the Ni to Co ratio has been found to have a strong effect on the martensite transition temperatures. Aging treatments cause Ni₃Ti₃ precipitates to form, which affect the martensite transition and subsequently the magnetization. The structure of most of the Fe-Ni-Co-Ti alloys tested showed lenticular martensite at room temperature with a single sample showing retained thin plate martensite in austenite after cooling to 77K.

Materials that develop large shape changes in the magnetic field at a short response time provide a new method of producing motion and force in electromechanical devices. The strains are based on the magnetic-field-induced reorientation of the twin variants of the material. This effect is called magnetic shape memory (MSM) effect, because the shape of the material can be controlled by the magnetic field. MSM effect can operate in the martensite phase, and it does not require temperature changes to occur unlike regular shape memory effect (SME). Ni-Mn-Ga alloys and several iron-based alloys are currently being developed by many research groups. In this report, magnetic-field-induced strain of two polycrystalline non-stoichiometric Ni₂MnGa alloys with oriented crystal structure were studied during cooling through the martensitic transformation temperature (M_s) and at a constant temperature below M_s. X-ray diffraction measurements confirmed that the origin of the induced strains was the change of the proportions of different twin orientations. Frequency response of the MSM strains in the alloy was shown to be over 5 kHz. One of the present alloys was deposited by laser ablation on a silicon substrate. The thin film exhibits tetragonal lattice structure.

A new theory is presented of the nonlinear magneto-elastic behavior of magnetically dilute magnetostrictive particulate composites. The theory assumes a uniform external magnetic field is operating on a large number of well distributed, crystallographically and shape parallel ellipsoidal magnetostrictive particles encased in an elastic, nonmagnetic composite matrix. The aspect ratio of the particulates may vary between 1 to infinity and the volume fraction of the particulates may vary between zero and one. Example calculations show that the model is able to provide qualitatively correct magnetostriction curves for both homogeneous Terfenol-D rod and experimental Terfenol-D particulate actuated epoxy matrix composites.

A sonar transducer, 28 mm in diameter and 40 mm long, has been built using composite Terfenol-D, consisting of grains of Terfenol-D embedded in an epoxy and magnetically aligned while the epoxy is setting. The transducer has been tested in air, where it has a resonant frequency of 18 kHz, and Q equals 18 at low amplitudes. In water it is expected to have Q equals 4.5, an acoustic output power of 48 watts, a power efficiency of 32 percent, and a maximum duty cycle of 6 percent. Surprisingly, hysteresis losses appear to be negligible when the bias field is greater than 800 oersteds, and 90 percent of the power dissipation is due to eddy currents, with 10 percent due to ohmic losses in the coil. The anomalously high eddy currents, still much lower than in monolithic Terfenol-D, can be understood in terms of the arrangement of Terfenol-D grains in the composite. At this time we have no explanation for the anomalously low hysteresis loss. It should be possible to greatly reduce the eddy currents, increasing the power efficiency to 76 percent, the output power to 69 watts, and the maximum duty cycle to 60 percent. Composite Terfenol-D should be superior to both monolithic Terfenol-D and PZT in transducers for sonar arrays operating in the 20 to 30 kHz range.

As SMA wires are gaining in popularity for use as actuators, one constitutive parameter that remain unknown is the thermomechanical fatigue life. Even though the effect of thermal cycles on the transformation characteristics of SMAs has been studied, these teste have not been extended to high number of cycles. In this study, a novel test frame developed to study the thermomechanical fatigue life of SMAs is described. Additionally, a testing protocol is discussed necessary to fully establish the fatigue characteristics of SMAs under various conditions. Initial results of the initial test show a substantial increase in the number of cycles to failure as the applied stress level reduces to approximately 100 MPa.

The mechanical properties of shape memory alloys (SMAs) are finding more and more attention in micro-system technology. However, only a few processes are available for machining of miniaturized SMA-components. During the machining process, changes of the shape memory properties due to the extension of the heat effected zone or mechanical tensions have to be avoided. Especially for complex geometries with dimensions in the submillimeter-range, these requirements are difficult to fulfill.

The present work reports macroscopic thermal mechanical and in-situ neutron diffraction measurements from a 22.9 volume percent, 50.7 at percent Ni-Ti fiber actuated 6082-T6 aluminum matrix composite and 6082-T6 homogeneous aluminum control material subjected to an initial room temperature 4 percent tensile elongation and unloading process followed by a subsequent room temperature to 120 degrees C unconstrained heating process. During the unconstrained room temperature to 120 degrees C heating process, the composite exhibited a pronounced, nonlinear thermal contraction, while the homogeneous control exhibited the expected linear thermal expansion. The composite thermal compression was clearly the result of a powerful shape memory response in the NiTi fiber actuators.

In this paper, the experimental study of a NiTi shape memory alloy bar with nominal diameter of 6.5 mm is presented. First, some torsion experiments, including torsion cycling at constant temperature and thermal cycling under constant torque, were carried out. In these test, the torque was applied in both positive and negative directions. Two-way memory behavior and some unique phenomena, such as kink and easy-training, were found and hence, a series of uniaxial tension test was performed in order to understand the observations. After presenting the experimental work, the reason behind these phenomena is discussed.

In this paper we will present a novel method for depositing NiTi thin film by DC sputtering that produces films with transformation temperatures very close to that of the target. The new process involves heating the target to temperatures over 400 degrees C and does not require compositional modification of the 50/50atm percent NiTi target. Results from tensile testing, XRD, TEM, and DSC are presented. Conclusions are cold target produces films that were in the Austenite phase at rom temperature while hot target produces films that were Martensite at room temperatures, confirming that compositional modification can be produced by varying the target temperature. Films that were produced by gradual heating of the target, produced a gradation of composition through the film thickness. These gradation films exhibiting the two-way SME. The simplicity of this new process should increase the use of NiTi film sin microactuator devices.

Transformation characteristics of near equiatomic, prior cold worked Nitinol have been studied through thermomechanical analysis and electrical resistivity measurements, using TMA-50 and a four-probe setup, respectively. The dilatometric and electrical resistivity curves are obtained for the samples heat-treated between 300 and 600 degrees C. Examination of the dilation curves show that, in the martensitic phase there is positive thermal expansion where as, during M yields A transformation there is also uniaxial contraction till A_f. In the austenitic phase there is positive thermal expansion and these thermal expansion values agree with the published values for respective phases. While cooling, at M_s uniaxial expansion starts and this continues till M_f is reached. In the present work the R-phase and associated hysteresis has also been investigated. On cooling from A-phase, uniaxial expansion is found to start from R_s and it stops at R_f. The transformation temperatures determined in this method agree very closely with those values obtained using electrical resistivity probe. Hysteresis area is found to be smaller in the A $ARLR M transformation. The area under hysteresis loop associated with R-phase is found to be a constant against thermal cycling. Certain applications like clamps and splints require a large hysteresis loop, while some solid sate actuators require relatively smaller hysteresis loops. An attempt is made to explain R-phase transformation in terms of thermo-mechanical data.

The effect of aging treatments on the microstructure, martensite transformation temperature and shape memory effects (SME) of the Ni₄₆Ti₄₄Ta₁₀ alloy was carefully studied in this work. The result show that the microstructure of Ni₄₆Ti₄₄Ta₁₀ alloy contains an NiTi phase, a eutectic structure, which formed by NiTi, and (beta) -Ta phase, and some dispersed NiTa₂ compound. The aging treatment can produce Ti₁₁Ni₁₄ precipitates in the alloy. Meanwhile, precipitation hardening was noticed during the aging process. The phase transformation temperatures and hardness of the sample alloy vary with the changing of the composition and redistribution of each phase during the aging treatments. After the aging treatment, the samples demonstrated an enhanced shape memory effect compared with untreated samples. It is also evident that there is a strong correspondence between the enhanced shape memory effect and the increase of the hardness value.

SMAs commonly hold a perceived downfall of low cyclic fatigue life, which is a significant design driver for SMA actuators. Some fatigue data is available for various types of cyclic loading, but little is applicable for use in actuators. ITN Energy Systems has done extensive fatigue testing directly applicable to SMA actuator design. In this paper, we compare our data to previous studies, and present practical guidelines to aid in the design of SMA actuators.

The property enhancement offered by single crystal relaxor ferroelectrics combined with the manufacturability advantages offered by injection molding has the potential of producing single crystal 1-3 piezocomposites at an affordable production-viable rate. Two methods of texturization/recrystallization are being evaluated: an integrated multi-seed process and epitaxial growth. The integrated seed approach involves incorporation of oriented single crystal PMN-PT seeds into injection molding feedstock prior to fabrication of 1-3 ceramic preforms. After sintering, an additional texturization and growth step is carried out. This step is intended to drive recrystallization at multiple sites within the ceramic body extending the oriented texture throughout the matrix. The epitaxial growth approach involves nucleation and growth in the dense ceramic body initiated from a compatible external seed crystal. Recrystallization is achieved through direct contact between a ceramic preform and a seed substrate coupled with appropriate thermal and atmospheric growth conditions.

Plasma-sprayed zirconia is widely used in aero-engines as thermal barrier coating material. The material has an open porosity and a network of very thin microcracks. The porosity and the microcracks give rise to the low elastic stiffness. When the plasm sprayed zirconia is immersed in a liquid the microcracks can be filled with the liquid by capillary forces. Although there is only a small amount of infiltrated material the zirconia shows a strong increase in elastic stiffness. We have measured the elastic behavior after infiltration and as function of temperature by ultrasonic pulse echo technique. It could be observed that the solidification of the infiltrated fluid at lower temperatures leads to a further increase of the elastic stiffness. The temperature controlled liquid-solid phase transition can therefore be used to change reversibly the elastic properties of this ceramic material. The desired switching temperature can be chosen by appropriate fluids. A possible application of this material is the vibration damping of coated structures by temperature controlled changing of resonance frequencies.

Cl₂ and O₃ gas detection at high sensitivity has been realized by newly developed thin-film gas sensors incorporating multicomponent oxides such as ZnO-In₂O₃, MgO-In₂O₃, and Zn₂In₂-MgIn₂O₄ systems. The sensors exhibited an increase in resistance with exposure to Cl₂ or O₃ gas. The sensing properties of the multicomponent oxide thin-film sensors were strongly dependent on the composition of the multicomponent oxide films used as well as the operating temperature. The highest sensitivity for Cl₂ and O₃ gases was obtained in sensors using a Zn₂In₂O₅- MgIn₂O₄ thin film prepared with Zn₂In₂O₅ contents of about 60 and 20 mol. percent respectively: Cl₂ gas detected at a minimum concentration of 0.01 and O₃ gas at 0.4ppm. A fast response as well as a high sensitivity were obtained in these sensors operated with alternating exposures in air and Cl₂ or O₃ gas. The resistivity, carrier concentration and Hall mobility of the thin-film sensors were measured under operation conditions using the van der Pauw method. It should be noted that a decrease or increase of resistivity in the thin-film sensors resulted from a simultaneously increase or decrease of both carrier concentration and Hall mobility. The increase in resistivity is attributed to the trapping of free electrons resulting from Cl₂ and O₃ being adsorbed on grain boundaries and/or the film surface, the same as that produced by adsorption of oxygen. A Zn₂In₂O₅- MgIn₂O₄ thin-film gas sensor exhibited very stable long term operation in an atmosphere with a high concentration of Cl₂ gas.

The thermo-mechanical characteristics of four NiTi based SMA torque tubes are investigated under simple torsional loading. Results from the thermo-mechanical tests are presented for samples when fully martensitic, fully austenitic, and recovery torque measurements. Test results indicate that wall thickness plays a prominent role in the results. An analytical model was developed as a function of geometry and experimentally determined material properties. The model predicts the torque versus angular deformation for a wide range of tube geometries when in martensite and austenite. The distribution of strain through the thickness is assumed to vary non-linearly as an exponentially with the radius. The analytical results reflect the mechanical behavior reasonably well.