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Author: Dennis Salvatore Agosta
Publisher:
ISBN:
Category : Nanocrystals
Languages : en
Pages : 246
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Author: Dennis Salvatore Agosta
Publisher:
ISBN:
Category : Nanocrystals
Languages : en
Pages : 246
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Author: Kenneth A. Pestka
Publisher:
ISBN: 9780542828034
Category :
Languages : en
Pages : 169
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Author: Guangyan Li
Publisher:
ISBN:
Category :
Languages : en
Pages : 416
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The goal of this dissertation is to elastically characterize thermoelectrics and other novel materials using resonant ultrasound spectroscopy (RUS) at elevated temperatures. A "direct-contact" transducer system with test sample in direct contact with the piezoelectric elements was developed. This new transducer system with improved signal-to-noise ratio (SNR) and the conventional buffer-rod system were used for elasticity measurements and phase transition studies. The temperature dependent elastic moduli of thermoelectric materials of four nanostructured polycrystalline silicon-germanium (SiGe) samples were obtained up to 950°C. Abnormal elastic behavior (stiffening) in the temperature range of 350-550°C was observed in the two n-doped SiGe samples, which is associated with dopant (phosphorus) precipitation. The elastic moduli of the complex Zintl phase Yb 14 MnSb 11 were also measured up to 600°C. Using the quick "mode-tracking" method, the various temperature-induced phase transitions in Yb 14 MnSb 11, transition metal oxide LuFe 2 O 4 and bulk metallic glass Zr 50 Cu 31 Pd 9 Al 10 were investigated. In addition to the high-temperature RUS measurements, the continuum elastic model in RUS was also applied to numerically study several lower normal modes of vibration in carbon nanotubes (CNTs).
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 5
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Author: Gautham Manoharan
Publisher:
ISBN:
Category :
Languages : en
Pages : 67
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The objective of this thesis is to validate Resonant Ultrasound Spectroscopy (RUS) as a non-destructive evaluation tool that can be used to study effects of radiation on the mechanical properties of a material, mainly its elastic constants. RUS involves experimentally measuring the resonant frequencies of a sample and calculating the elastic constants based on these measurements. Finite Element Method (FEM) is used to get the frequencies of the modes of free vibration for the sample model. This result depends on the elastic constant values used in the FEM simulation. Studies were conducted to confirm the accuracy of the FEM model, and determine the right configuration and parameters to use for the simulation. Assuming uniform and isotropic elastic property changes, the effects of radiation damage can be quantified by obtaining a set of matching resonant frequencies between the experimental and FEM simulation results, before and after irradiating the sample. This is done by adjusting the elastic constant values used in the simulation so that the results match with the experimentally obtained resonant frequencies. With powerful enough equipment, even real time monitoring is possible in harsh environments, thus pointing out imminent failure.
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 28
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Department of Energy EPSCoR The University of Mississippi Award: DE-FG02-04ER46121 Resonant Ultrasound Spectroscopy Studies of Complex Transition Metal Oxides The central thrust of this DOE funded research program has been to apply resonant ultrasound spectroscopy (RUS), an elegant and efficient method for determining the elastic stiffness constants of a crystal, to the complex and poorly understood class of materials known as transition metal oxides (TMOs). Perhaps the most interesting and challenging feature of TMOs is their strongly correlated behavior in which spin, lattice, and charge degrees of freedom are strongly coupled. Elastic constants are a measure of the interatomic potentials in a crystal and are thus sensitive probes into the atomic environment. This sensitivity makes RUS an ideal tool to study the coupling of phase transition order parameters to lattice strains. The most significant result of the project has been the construction of a high temperature RUS apparatus capable of making elastic constant measurements at temperatures as high as 1000 degrees Celsius. We have designed and built novel acoustic transducers which can operate as high as 600 degrees Celsius based on lithium niobate piezoelectric elements. For measurement between 600 to 1000 C, a buffer rod system is used in which the samples under test and transducers are separated by a rod with low acoustic attenuation. The high temperature RUS system has been used to study the charge order (CO) transition in transition metal oxides for which we have discovered a new transition occurring about 35 C below the CO transition. While the CO transition exhibits a linear coupling between the strain and order parameter, this new precursor transition shows a different coupling indicating a fundamentally different mechanism. We have also begun a study, in collaboration with the Jet Propulsion Laboratory, to study novel thermoelectric materials at elevated temperatures. These materials include silicon germanium with various doping and Zintl phase materials. Such materials show promise for increased figures of merit, vital to making thermolectrics competitive with traditional power generation mechanisms.
Author: Robert G. Leisure
Publisher: Cambridge University Press
ISBN: 1108228712
Category : Science
Languages : en
Pages : 249
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Book Description
Ultrasonic spectroscopy is a technique widely used in solid-state physics, materials science, and geology that utilizes acoustic waves to determine fundamental physical properties of materials, such as their elasticity and mechanical energy dissipation. This book provides complete coverage of the main issues relevant to the design, analysis, and interpretation of ultrasonic experiments. Topics including elasticity, acoustic waves in solids, ultrasonic loss, and the relation of elastic constants to thermodynamic potentials are covered in depth. Modern techniques and experimental methods including resonant ultrasound spectroscopy, digital pulse-echo, and picosecond ultrasound are also introduced and reviewed. This self-contained book includes extensive background theory and is accessible to students new to the field of ultrasonic spectroscopy, as well as to graduate students and researchers in physics, engineering, materials science, and geophysics.
Author: Keir Foster
Publisher:
ISBN:
Category : Condensed matter
Languages : en
Pages : 384
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Author: Jyrki Vuorinen
Publisher:
ISBN: 9789521506710
Category :
Languages : en
Pages : 36
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Author: 鄭鴻輝
Publisher:
ISBN:
Category :
Languages : en
Pages : 95
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