Solid State Phenomena Vol. 185

Abstract: We explore the kinetics of a three-state strain pseudospin model for a square/rectangle ferroelastic transition, described by a temperature dependent hamiltonian without quenched disorder, using temperature quench Monte Carlo simulations. The model hamiltonian includes power law anisotropic long range interactions, which lock the domain walls in a symmetry breaking diagonal direction. In athermal parameter regime, there are fast conversions at the athermal transition temperature, but with delay tails above it, as in experiment. The conversion delay tails have a Vogel-Fulcher divergence at transition to austenite. The incubation delays and their insensitivity to elastic energy scales are attributed to entropy barriers. Temperature cycling shows hysteretic behavior in physical quantities.

Abstract: Fabric materials can be in form of woven, knitted, non-woven and braided structures or a combination of these structures can be used for protective fabric. Properties of fabrics depend on the different types of fibres that constitute the fabric and the geometry of the final structure. This project seeks the development of optimally woven enhanced silk fabric for high performance application that can be potentially beneficial to various engineering fields such as ballistic protection for military, aerospace, automotive, sports and marine engineering industries. Natural enhanced silk will be used as the yarns, rather than the traditionally used synthetically produced aramid material which poses an environmental problem. The tensile strength, tensile modulus and elongation of yarns strength are the main influences on ballistic performance. In addition to the tensile properties of the yarn, fabric weave structure is crucial as propagation of stress waves is affected by the weave structure. Mechanical performance of the woven silk fabric of various designs will be subsequently accessed for their effectiveness based on tensile testing and ballistic testing.

Abstract: n-doped ZnO (ZnO:In) thin films with 0~9at.% In content have been prepared by RF high magnetron sputtering on glass substrate. All the films were annealed in N₂ at 473K for 1h. The effect of In doping concentration on the structure, surface morphology, electrical properties,Seebeck and magnetoresistive effect of the films were investigated. It was found that the crystal quality of the films degrades, and the surface gets rough with increasing In content. The lowest resistivity of the ZnO:In thin films 6.1×10^-4Ω.cm occurs at 5at.% in the target doping concentration. All the films show a striking Seebeck effect and the absolute value of the Seebeck coefficient decreases under magnetic field. Meanwhile, a positive magnetoresistance of the films was found. ZnO thin films with 1at.% In-doped is best for the thermoelectric material, which has the largest power factor of 2.1×10^-4W/K²m at room temperature.

Abstract: Yb³⁺ doped YAG ceramics have been successfully fabricated using a vacuum reactive sintering method. High purity Y₂O₃, Al₂O₃ and Yb₂O₃ powders were used as the starting materials. Samples of 5.0 at.% Yb³⁺ doping concentration have been obtained. The in-line transmittance of the sample reaches 84% at 1100 nm wavelength. The absorption and emission bandwidth were measured to be 19.5 nm and 11.07 nm respectively. The results show that Yb:YAG ceramics will be a promising laser material for high power and ultrafast laser applications.

Abstract: A modified Florence model to predict ballistic limit velocity (BLV) for bi-layer armor systems comprising ceramic front and metallic backing plate is proposed based on energy conservation. Maximization of the BLV for a given AD or TT is studied. Comparison between the maximum BLV obtained from new model, two other available models in the literature and experiments is performed. It is shown that the new model, Energy model compares well to the experimental data. Keywords: Impact; perforation; optimization; bi-layer armor system

Abstract: High quality holmium doped Yttrium Aluminum Garnet (YAG) transparent ceramics were fabricated by a reactive sintering method under vacuum. Fully dense Ho:YAG ceramics with the average grain size of ~ 10 μm were obtained after vacuum sintering at 1780 for 8 h. The optical properties, microstructures and photoluminescence spectra of the fabricated Ho:YAG ceramics were investigated. The transmittances of Ho:YAG ceramic are higher than 82% at 400 nm and 84% at 2400 nm. The absorption coefficient was 1.32 cm^-1 for 1.5 at.% Ho:YAG at 1907 nm. And the absorption cross section of the Ho:YAG ceramic is 0.645×10^-20 cm².

Abstract: Highly transparent Er:YAG ceramics with different Er concentration were fabricated by a solid-state reaction and vacuum sintering method. The optical properties, the microstructure and the upconversion luminescence of the Er:YAG ceramics were investigated. For 3 mm thick samples, the in-line transmittances of the as-fabricated Er:YAG ceramics at the wavelength of 1100 nm and 400 nm were about 84% and 82%, respectively, which was very close to the theoretical transmittance of YAG ceramics. The micrograph of the Er:YAG transparent ceramics exhibited a pore-free structure and the average grain size was about 10 μm. The grain boundary of the ceramics was clean and no secondary phase was detected. When pumped by a 980 nm LD, the strong green and red upconversion luminescences in the Er:YAG ceramics were observed. The different upconversion mechanisms depending on Er concentration in the Er:YAG ceramics were also discussed.

Abstract: (100)-oriented PLZT ((Pb_1-x, La_x) (Zr_y,Ti_1-y)_1-x/4O₃, x/y=9/65) films of up to ~ 1.23 μm have been developed on LaAlO₃ single crystal substrate by magnetron sputtering. The as-grown PLZT thin films exhibit high optical transparency in visible and near-infrared light wavelength and high quadratic (Kerr) EO coefficients. Prism coupler measurements reveal that the PLZT thin films possess large refractive index, as high as 2.524 in TE model and 2.481 in TM model. The transparency of >70% in the range of λ= 500-1200 nm, the optic band gap of 3.42 eV and the quadratic electro-optic (EO) coefficient of 3.38 x 10^-17 (m/V)² have been measured in the films. Due to the large EO coefficient and the micrometric thickness, the as-developed PLZT films have great potential in developing longitudinal-or transverse-type EO devices in electric and optic field

Abstract: Lead Zirconium Titanate (PZT) is an example of a piezoelectric material, which can be polarized by an electric field or mechanical stress. This study aims to establish how doping PZT with Strontium will result in PSZT thin films with improved piezoelectric properties for biomedical tactile sensor applications. Various thin film samples were fabricated via sol-gel & spin-coating processing methods-PZT (4 layers), PSZT (4 layers), PSZT-PZT (2L PSZT base-2L PZT) and PZT-PSZT (2L PZT base-2L PSZT), analyzed by X-Ray Diffraction (XRD) and Atomic Force Microscopy (AFM) to determine crystalline structure and surface morphology, and by a ferroelectric analyzer to determine leakage current characteristics and ferroelectric parameters such as P_max, P_r and V_c (representation of piezoelectric properties). The addition of Strontium retains the perovskite structure of PZT and marginally influences the ferroelectric properties. Among the hybrid films, PZT(base)-PSZT showed better ferroelectric characteristics (higher P_max and P_r values). A mathematical relationship between the ferroelectric parameters (P_r and V_c) to evaluate the films quality factor in relation to their application as tactile sensors, was also established, from which it was concluded that PZT-PSZT performs much better than the other 3 films for such applications despite high V_c values. The improved performance of hybrids may be due to the evolved microstructure and crystalline structure. Present investigation resulted in two important conclusions: PZT-PSZT hybrid films are ideal for tactile sensor applications, and the mathematical relationship developed can be used to evaluate any piezoelectric/ferroelectric materials.

Abstract: This article reports the development of ZnO coated one port Surface Acoustic Wave (SAW) resonators for the detection of DMMP (dimethyl methyl phosphonate), a simulant of chemical warfare agent Sarin at room temperature. For enhanced sensitivity high frequency SAW devices (433Mhz) were used. Frequency shift with DMMP exposure was found to increase with increase in thickness of ZnO film from 20 to 80 nm with maximum shift of 52 kHz. The cross sensitivity of the sensor with commonly available volatile organic compounds (VOCs), gases and water vapors has been performed and was found that the sensitivity towards other interferants is very less as compared to that of DMMP vapors. The sensing mechanism has been explained in detail. It has been shown that there was no significant change in the resistance of the film with exposure to DMMP vapors and hence the contribution of the acoustoelectric interaction is negligible. Further mass loading was not dominant. The negative differential frequency shifts proved that change in elasticity of the film with exposure to DMMP vapors is the dominant sensing mechanism.