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153. Investigation of Electric Field-Induced Structural Changes at Fe-Doped SrTiO3 Anode Interfaces by Second Harmonic Generation.

Author

Ascienzo, David, Yuan, Haochen, Greenbaum, Steve, Bayer, Thorsten J. M., Maier, Russell A., Wang, Jian-Jun, Randall, Clive A., Dickey, Elizabeth C., Haibin Zhao, and Yuhang Ren

Subjects
SECOND harmonic generation, ANODES, STRONTIUM titanate, ELECTROSTRICTION, PEROVSKITE, OXIDES
Abstract

We report on the detection of electric field-induced second harmonic generation (EFISHG) from the anode interfaces of reduced and oxidized Fe-doped SrTiO3 (Fe:STO) single crystals. For the reduced crystal, we observe steady enhancements of the susceptibility components as the imposed dc-voltage increases. The enhancements are attributed to a field-stabilized electrostriction, leading to Fe:Ti-O bond stretching and bending in Fe:Ti-O6 octahedra. For the oxidized crystal, no obvious structural changes are observed below 16 kV/cm. Above 16 kV/cm, a sharp enhancement of the susceptibilities occurs due to local electrostrictive deformations in response to oxygen vacancy migrations away from the anode. Differences between the reduced and oxidized crystals are explained by their relative oxygen vacancy and free carrier concentrations which alter internal electric fields present at the Pt/Fe:STO interfaces. Our results show that the optical SHG technique is a powerful tool for detecting structural changes near perovskite-based oxide interfaces due to field-driven oxygen vacancy migration. [ABSTRACT FROM AUTHOR]

Published
2016
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155. Preface

Author

Dickey, Elizabeth C., primary, Berger, Marie-Hélène, additional, Merino, Rosa I., additional, and Goto, Takashi, additional

Published
2014
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157. Thermally Stable Nanometals by Predictive Atomic Scale Interfacial Energy Reduction

Author

ARMY RESEARCH LAB ABERDEEN PROVING GROUND MD WEAPONS AND MATERIALS RESEARCH DIRECTORATE, Darling, Kris, Kecskes, Laszlo, Liu, Zi-Kui, Dickey, Elizabeth, Li, Jing, ARMY RESEARCH LAB ABERDEEN PROVING GROUND MD WEAPONS AND MATERIALS RESEARCH DIRECTORATE, Darling, Kris, Kecskes, Laszlo, Liu, Zi-Kui, Dickey, Elizabeth, and Li, Jing

Abstract

Nanocrystalline iron (Fe) alloys doped with 1 at.% zirconium (Zr), tantalum (Ta), and nickel (Ni), produced through high energy mechanical alloying, were investigated for microstructural stability. The results were consistent with theoretical predictions, indicating a decrease in stability with solute type in the following order: Zr, Ta, and Ni. Preliminary transmission electron microscopy (TEM) investigations of the most stable system, Fe-Zr, revealed the presence of 2.5 at.% Zr within the grain boundaries of the sample, confirming a thermodynamic tendency for stability. More specifically, Zr segregation was found to be inhomogenously distributed between grain boundaries of nanostructured regions. Such a distribution accounts for and provides a potential mechanism for the appearance of abnormal grain growth at elevated temperatures. Additional compositional profiling uncovered a new FCC phase, within the abnormally grown grains. This phase is coherent with the BCC Fe substrate matrix and has a lattice parameter of 8.5 A., The original document contains color images.

Published
2011

160. Effect of c-Si doping density on heterojunction with intrinsic thin layer (HIT) radial junction solar cells

Author

Shen, Haoting, primary, Yuwen, Yu, additional, Wang, Xin, additional, Ramirez, J. Israel., additional, Li, Yuanyuan V., additional, Ke, Yue, additional, Kendrick, Chito E., additional, Podraza, Nikolas J., additional, Jackson, Thomas N., additional, Dickey, Elizabeth C., additional, Mayer, Theresa S., additional, and Redwing, Joan M., additional

Published
2013
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161. Microstructure and dielectric properties with CuO additions to liquid phase sintered BaTiO3 thin films.

Author

Harris, David T., Burch, Matthew J., Mily, Edward J., Dickey, Elizabeth C., and Maria, Jon-Paul

Subjects
COPPER oxide, SINTERING, MICROSTRUCTURE, BARIUM titanate films, DIELECTRIC properties, GRAIN size
Abstract

The refractory nature of BaTiO3 leads to limited densification and grain growth for films processed at low temperatures and a modest nonlinear dielectric response due to a marked sensitivity to physical scale and material quality. Adding liquid-forming sintering aids, common in bulk ceramics, to thin films enhances mass transport, leading to enhanced grain growth at lower temperatures. This work explores the effectiveness of a sputtered CuO buffer layer with BaO-B2O3 (BBO) fluxes to engineer the microstructure of BaTiO3 films. Grain size and homogeneity increase in the presence of even a ~1 nm CuO layer. In general, grain size increases from 75 to 370 nm with an addition of 2.2% BBO and 8 nm CuO. Room temperature capacitance in fluxed films increases by a factor of 5 over pure films, and ferroelectric phase transitions are clearly observable in dielectric measurements. CuO-BBO proves effective on (0001) Al2O3 and (100) MgO substrates, although all microstructures are notably finer for the latter. [ABSTRACT FROM AUTHOR]

Published
2016
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166. Parametric study of micropillar array solar cells

Author

Yoon, Heayoung P., primary, Yuwen, Yu A., additional, Shen, Haoting, additional, Podraza, Nikolas J., additional, Mallouk, Thomas E., additional, Dickey, Elizabeth C., additional, Redwing, Joan A., additional, Wronski, Christopher R., additional, and Mayer, Theresa S., additional

Published
2011
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171. X-ray Diffractometer for Texture and Residual Stress Studies of Advanced Materials

Author

PENNSYLVANIA STATE UNIV UNIVERSITY PARK DEPT OF MATERIALS SCIENCE AND ENGINEERING, Dickey, Elizabeth C., PENNSYLVANIA STATE UNIV UNIVERSITY PARK DEPT OF MATERIALS SCIENCE AND ENGINEERING, and Dickey, Elizabeth C.

Abstract

Through AFOSR DURIP grant # F49620-00-1-0245, a four circle goniometer x-ray diffractometer outfitted with a high temperature stage was purchased from Philips Analytical. The instrumentation facilitates residual stress measurements in highly textured materials up to 900 deg C. The instrument has significantly enhanced the AFOSR funded research efforts of the Pl on directionally solidified ceramic eutectics. Initial studies have measured the residual stresses in highly textured AlO3-ZrO2(Y2O3) eutectics as a function of temperature. At room temperature, significant compressive stresses (^450 MPa) are present in Al2O3 with corresponding tensile stresses in ZrO2. Through high temperature studies, the stress-free temperature was found to be ^675 deg C.

Published
2003

179. Hot Isostatic Pressing of Transparent Nd:YAG Ceramics

Author

Lee, Sang-Ho, primary, Kupp, Elizabeth R., additional, Stevenson, Adam J., additional, Anderson, Julie M., additional, Messing, Gary L., additional, Li, Xin, additional, Dickey, Elizabeth C., additional, Dumm, John Q., additional, Simonaitis-Castillo, Vida K., additional, and Quarles, Gregory J., additional

Published
2009
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181. A Non-Traditional Vapor-Liquid-Solid Method for Bulk Synthesis of Semiconductor Nanowires

Author

LOUISVILLE UNIV KY DEPT OF CHEMICAL ENGINEERING, Sharma, Shashank, Sunkara, Mahendra K., Lian, Guoda, Dickey, Elizabeth C., LOUISVILLE UNIV KY DEPT OF CHEMICAL ENGINEERING, Sharma, Shashank, Sunkara, Mahendra K., Lian, Guoda, and Dickey, Elizabeth C.

Abstract

Multiple silicon nanowires were synthesized using large gallium pools and microwave plasma. Results showed that nanowires growing out of different sized large gallium drops show little variation in diameters, suggesting that our non-traditional technique can he used to synthesize hulk amounts of monodispersed nanowires out of thin films of molten gallium., Pub in: Materials Research Society Symposium Proceedings, Volume 703. Prepared in collaboration with the Univ. of Kentucky, Dept. of Chemical and Materials Engineering, Lexington, KY. This article is from ADA401575 Nanophase and Nanocomposite Materials IV held in Boston, Massachusetts on November 26-29, 2001

Published
2001

182. LETTERS.

Author

WRIGHT, MILDRED SHEPARD, AMBROZ, A. O., DICKEY, ELIZABETH, ROSS, CHARLES G., SAUNDER, JOHN MONK, THOMPSON, RUTH ABBE, RALSTON, H. W., Ducks, Gulls v., and HARRIMAN, F. W.

Subjects
CATHOLICS, BAPTISTS, FAITH
Published
1931

190. Raman Scattering from Si1-xGexAlloy Nanowires

Author

Lu, Qiujie, primary, Adu, Kofi W., additional, Gutiérrez, Humberto R., additional, Chen, Gugang, additional, Lew, Kok-Keong, additional, Nimmatoori, Pramod, additional, Zhang, Xi, additional, Dickey, Elizabeth C., additional, Redwing, Joan M., additional, and Eklund, Peter C., additional

Published
2008
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192. Scanning Electron Microscopy of Nanoscale Chemical Patterns

Author

Srinivasan, Charan, primary, Mullen, Thomas J., additional, Hohman, J. Nathan, additional, Anderson, Mary E., additional, Dameron, Arrelaine A., additional, Andrews, Anne M., additional, Dickey, Elizabeth C., additional, Horn, Mark W., additional, and Weiss, Paul S., additional

Published
2007
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196. Low-Temperature Control of Twins and Abnormal Grain Growth in BaTiO3.

Author

Harris, David T., Burch, Matthew J., Li, Jing, Dickey, Elizabeth C., Maria, Jon‐Paul, and Viehland, D.

Subjects
LOW temperatures, METAL crystal growth, MICROSTRUCTURE, POLYCRYSTALS, BARIUM titanate films, CRYSTAL morphology
Abstract

The microstructure of polycrystalline barium titanate (BaTiO3) thin films processed with a liquid-phase can be controlled by the crystallographic orientation of the underlying sapphire substrate. During postdeposition crystallization, the tendency for {111} twin nucleation, which drives subsequent abnormal grain growth, depends upon the specific sapphire facet. Specifically, tilting away from the close-packed c-plane modifies the orientation, morphology, and relative amount of an interfacial BaAl2O4 second phase. These factors control the density of twin formation, and thus overall grain size of the crystallized BaTiO3. As the substrate orientation transitions from c-plane, to r-plane, to a-plane, the twin density is reduced, the average grain size decreases systematically from 270 to 130 nm, and the grain structure becomes overall more homogeneous. This twinning mechanism and abnormal grain growth occur by 900°C, several hundred degrees lower than reported previously. [ABSTRACT FROM AUTHOR]

Published
2015
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197. Growth and Microstructure-Dependent Hardness of Directionally Solidified WC-W2C Eutectoid Ceramics.

Author

Chen, Wei ‐ Ting, Meredith, Caleb H., Dickey, Elizabeth C., and Trice, R.

Subjects
CRYSTAL growth, METAL microstructure, HARDNESS, DIRECTIONAL solidification, TUNGSTEN carbide, CERAMIC materials
Abstract

Directionally solidified WC-W2C ceramics containing 40 at% carbon, corresponding to the WC-W2C eutectoid composition, were produced by laser surface melt processing. The resulting microstructures showed a lamellar-type eutectic/eutectoid microstructure with the WC minor phase embedded in the W2C matrix phase. The interlamellar spacing (λ) in the eutectoid regions followed the relationship Vλ3.8 = constant, with the smallest spacing of 331 ± 36 nm achieved in the 3.24 mm/s processed sample. The indentation hardness increased with decreasing interlamellar spacing, and a Vickers indentation hardness of 28.5 GPa was achieved in the sample with the smallest interlamellar spacing. The directionally solidified WC-W2C materials show enhanced indentation mechanical properties in comparison to previously reported WC-Co composites and WC-based materials. [ABSTRACT FROM AUTHOR]

Published
2015
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198. Fundamental Structure-Property Relationships for High-Temperature Ceramic Composites

Author

KENTUCKY UNIV LEXINGTON DEPT OF MATERIALS AND SCIENCE ENGINEERING, Dickey, Elizabeth C., KENTUCKY UNIV LEXINGTON DEPT OF MATERIALS AND SCIENCE ENGINEERING, and Dickey, Elizabeth C.

Abstract

Directionally-solidified oxide eutectics such as alumina-YAG and alumina-zirconia show promise as high-temperature structural materials because of their high temperature strength and creep resistance. 1-5 Compatibility constraints at the internal interfaces between the two constituent phases can lead to residual stresses upon thermal cycling and elastic interaction stresses under applied loads. The magnitudes and distributions of these stresses have important ramifications for the mechanical behavior of the composites. Here we investigate thermal stresses in alumina-YAG and alumina-zirconia directionally solidified eutectics (DSEs). First, the microstructure and crystallography are thoroughly characterized. X-ray diffraction is employed to measure the strain tensors in each phase, which are subsequently converted to stress tensors. Since the experimental measurements provide only average stresses in each phase, anisotropic finite element modeling (FEM) is used to investigate stress distributions in the materials. Comparisons between the experimental measurements and FEM results provide insight into possible stress relief.

Published
1999

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