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Articles 1 - 10 of 10
Full-Text Articles in Engineering
Electric Field-Induced Tetragonal To Orthorhombic Phase Transitions In [110]C-Oriented Batio₃ Single Crystals, D. J. Franzbach, Yijia Gu, Long-Qing Chen, K. G. Webber
Electric Field-Induced Tetragonal To Orthorhombic Phase Transitions In [110]C-Oriented Batio₃ Single Crystals, D. J. Franzbach, Yijia Gu, Long-Qing Chen, K. G. Webber
Materials Science and Engineering Faculty Research & Creative Works
Electric field-induced phase transitions in [110]c-oriented BaTiO3 single crystals were studied by macroscopic electrical measurements in the temperature range from 20 °C to 50 °C. Discontinuous, hysteretic jumps in the polarization and strain were observed, indicating a tetragonal ↔ orthorhombic phase transition. The critical electric field to induce the transition was found to shift to higher values with increasing temperature. The Landau-Devonshire theory was used to analyze the observed electric field-induced T ↔ O phase transitions.
Freeze-Form Extrusion Fabrication Of Functionally Graded Material Composites Using Zirconium Carbide And Tungsten, Ang Li, Aaron S. Thornton, Bradley K. Deuser, Jeremy Lee Watts, Ming-Chuan Leu, Greg Hilmas, Robert G. Landers
Freeze-Form Extrusion Fabrication Of Functionally Graded Material Composites Using Zirconium Carbide And Tungsten, Ang Li, Aaron S. Thornton, Bradley K. Deuser, Jeremy Lee Watts, Ming-Chuan Leu, Greg Hilmas, Robert G. Landers
Materials Science and Engineering Faculty Research & Creative Works
Ultra-high-temperature ceramics are being investigated for future use in aerospace applications due to their superior thermo-mechanical properties, as well as their oxidation resistance, at temperatures above 2000⁰C. However, their brittleness makes them susceptible to thermal shock failure. As graded composites, components fabricated as functionally-graded materials (FGMs) can combine the superior properties of ceramics with the toughness of an underlying refractory metal. This paper discusses the grading of two materials through the use of a Freeze-form Extrusion Fabrication (FEF) system to build FGM parts consisting of zirconium carbide (ZrC) and tungsten (W). Aqueous-based colloidal suspensions of ZrC and W were developed …
Conductivity Of Twin-Domain-Wall/Surface Junctions In Ferroelastics: Interplay Of Deformation Potential, Octahedral Rotations, Improper Ferroelectricity, And Flexoelectric Coupling, Eugene A. Eliseev, Anna N. Morozovska, Yijia Gu, Albina Borisevich, Long-Qing Chen, For Full List Of Authors, See Publisher's Website.
Conductivity Of Twin-Domain-Wall/Surface Junctions In Ferroelastics: Interplay Of Deformation Potential, Octahedral Rotations, Improper Ferroelectricity, And Flexoelectric Coupling, Eugene A. Eliseev, Anna N. Morozovska, Yijia Gu, Albina Borisevich, Long-Qing Chen, For Full List Of Authors, See Publisher's Website.
Materials Science and Engineering Faculty Research & Creative Works
Electronic and structural phenomena at the twin-domain-wall/surface junctions in the ferroelastic materials are analyzed. Carriers accumulation caused by the strain-induced band structure changes originated via the deformation potential mechanism, structural order parameter gradient, rotostriction, and flexoelectric coupling is explored. Approximate analytical results show that inhomogeneous elastic strains, which exist in the vicinity of the twin-domain-wall/surface junctions due to the rotostriction coupling, decrease the local band gap via the deformation potential and flexoelectric coupling mechanisms. This is the direct mechanism of the twin-wall static conductivity in ferroelastics and, by extension, in multiferroics and ferroelectrics. On the other hand, flexoelectric and rotostriction …
Method For Producing Pressurelessly Sintered Zirconium Diboride/Silicon Carbide Composite Bodies, Shi C. Zhang, Greg Hilmas, William Fahrenholtz
Method For Producing Pressurelessly Sintered Zirconium Diboride/Silicon Carbide Composite Bodies, Shi C. Zhang, Greg Hilmas, William Fahrenholtz
Materials Science and Engineering Faculty Research & Creative Works
A method of sintering a ZrB2-SiC composite body at ambient pressures, including blending a first predetermined amount of ZrB2 powder with a second predetermined amount of SiC powder, wherein both powders are characterized by the presence of surface oxide impurities. Next the blended powders are mixed to yield a substantially homogeneous powder mixture and a portion of the substantially homogeneous powder mixture is formed into a green body. The body is fired to a first temperature, wherein substantially all surface oxide impurities are reduced and/or volatilized to substantially eliminate oxides from the green body, and the body …
Spin Diffusion In Bulk Gan Measured With Mnas Spin Injector, Shafat Jahangir, Fatih Dogan, Hyun Kum, Aurelien Manchon, Pallab Bhattacharya
Spin Diffusion In Bulk Gan Measured With Mnas Spin Injector, Shafat Jahangir, Fatih Dogan, Hyun Kum, Aurelien Manchon, Pallab Bhattacharya
Materials Science and Engineering Faculty Research & Creative Works
Spin injection and precession in bulk wurtzite n-GaN with different doping densities are demonstrated with a ferromagnetic MnAs contact using the three-terminal Hanle measurement technique. Theoretical analysis using minimum fitting parameters indicates that the spin accumulation is primarily in the n-GaN channel rather than at the ferromagnet (FM)/semiconductor (SC) interface states. Spin relaxation in GaN is interpreted in terms of the D'yakonov-Perel mechanism, yielding a maximum spin lifetime of 44 ps and a spin diffusion length of 175 nm at room temperature. Our results indicate that epitaxial ferromagnetic MnAs is a suitable high-temperature spin injector for GaN.
Effects Of Rare-Earth Doping On Femtosecond Laser Waveguide Writing In Zinc Polyphosphate Glass, Luke B. Fletcher, Jon J. Witcher, Neil Troy, Signo Tadeu Dos Reis, Richard K. Brow, Denise M. Krol
Effects Of Rare-Earth Doping On Femtosecond Laser Waveguide Writing In Zinc Polyphosphate Glass, Luke B. Fletcher, Jon J. Witcher, Neil Troy, Signo Tadeu Dos Reis, Richard K. Brow, Denise M. Krol
Materials Science and Engineering Faculty Research & Creative Works
We have investigated waveguide writing in Er-Yb doped zinc polyphosphate glass using a femtosecond laser with a repetition rate of 1 KHz. We find that fabrication of good waveguides requires a glass composition with an O/P ratio of 3.25. The dependence on laser writing parameters including laser fluence, focusing conditions, and scan speed is reported. Waveguide properties together with absorption and emission data indicate that these glasses can be used for the fabrication of compact, high gain amplifying devices.
Phenomenological Thermodynamic Potential For Catio₃ Single Crystals, Yijia Gu, Karin Rabe, Eric Bousquet, Venkatraman Gopalan, Long-Qing Chen
Phenomenological Thermodynamic Potential For Catio₃ Single Crystals, Yijia Gu, Karin Rabe, Eric Bousquet, Venkatraman Gopalan, Long-Qing Chen
Materials Science and Engineering Faculty Research & Creative Works
The antiferrodistortive (AFD) structural transitions of calcium titanate (CaTiO3) at ambient pressure have been extensively studied during the last few years. It has been found that none of the AFD polymorphs is polar or ferroelectric. However, it was recently shown theoretically and later experimentally confirmed that a ferroelectric transition in CaTiO3 can be induced by tensile strains. The ferroelectric instability is believed to be strongly coupled to the AFD soft modes. In this paper, we present a complete thermodynamic potential for describing the coupling between the AFD and ferroelectric phase transitions. We analyzed the dependence of transition …
High-Density Pressurelessly Sintered Zirconium Diboride/Silicon Carbide Composite Bodies And A Method For Producing The Same, Shi C. Zhang, Greg Hilmas, William Fahrenholtz
High-Density Pressurelessly Sintered Zirconium Diboride/Silicon Carbide Composite Bodies And A Method For Producing The Same, Shi C. Zhang, Greg Hilmas, William Fahrenholtz
Materials Science and Engineering Faculty Research & Creative Works
A method of sintering a ZrB2-SiC composite body at ambient pressures, including blending a first predetermined amount of ZrB2 powder with a second predetermined amount of SiC powder, wherein both powders are characterized by the presence of surface oxide impurities. Next the blended powders are mixed to yield a substantially homogeneous powder mixture and a portion of the substantially homogeneous powder mixture is formed into a green body. The body is fired to a first temperature, wherein substantially all surface oxide impurities are reduced and/or volatilized to substantially eliminate oxides from the green body, and the body …
Effective Dielectric Constant Of Two Phase Systems, Vladimir Petrovsky, Piotr Z. Jasinski, Fatih Dogan
Effective Dielectric Constant Of Two Phase Systems, Vladimir Petrovsky, Piotr Z. Jasinski, Fatih Dogan
Materials Science and Engineering Faculty Research & Creative Works
Theoretical approaches to electrical characterization of two phase systems are mostly limited to the systems where the individual components exhibit the same type of conductivity (pure dielectric or pure conductive systems). In this article, the brick wall geometry is extended to the mixed conductive systems with percolation. Impedance spectroscopy techniques were used for experimental investigation of slurries. Various metal oxide powders and host liquids were analyzed using a wide range of solids loadings. Comparison of experimental results with theoretical predictions shows good fitting of the experimental data. Parameters (the values of permittivity for both phases and percolation threshold) calculated from …
Deposition Of Cerium-Based Conversion Coatings On Aluminum Alloy 380, Ci Lin, Surender Maddela, William Fahrenholtz, Matthew O'Keefe
Deposition Of Cerium-Based Conversion Coatings On Aluminum Alloy 380, Ci Lin, Surender Maddela, William Fahrenholtz, Matthew O'Keefe
Materials Science and Engineering Faculty Research & Creative Works
Cerium-based conversion coatings were deposited on as-cast aluminum alloy 380 substrates by a spontaneous immersion process. In this study, the effects of rinsing temperature prior to immersion in the coating deposition solution were studied with respect to the surface morphology, electrochemical response, and corrosion resistance of the coatings. Panels rinsed at 25 degrees celsius prior to coating had large cracks and holes in the coating. In contrast, panels rinsed at 100 degrees celsius prior to coating had a uniform coating morphology with fewer, smaller cracks. Electrochemical testing revealed that coatings deposited on substrates rinsed at 100 degrees celsius had higher …