Bulletin of the American Physical Society
2006 73rd Annual Meeting of the Southeastern Section of the APS
Thursday–Saturday, November 9–11, 2006; Williamsburg, Virginia
Session BA: Solid State NMR |
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Chair: Gina Hoatson, College of William & Mary Room: Williamsburg Hospitality House Empire A/B |
Thursday, November 9, 2006 8:30AM - 9:00AM |
BA.00001: Local Structure in PMSN Across the Ferroelectric Phase Transition Invited Speaker: Local structure and $^{93}$Nb ion displacement play vital roles in the ferroelectric polarization and phase transitions of solid solutions with composition (1-x)PbMg$_{1/3}$Nb$_{2/3}$O$_{3 }$-- x PbSc$_{1/2}$Nb$_{1/2}$O$_{3}$ (PMSN). Here, we report variable temperature, high field (17.6Tesla) $^{93}$Nb MAS and 3QMAS NMR studies of PMSN with compositions between x = 0.6 and 0 (pure PMN). In PMSN, six narrow components and one broad peak were observed. Spectral assignments agree with previous reports [D.H.Zhou, G.L.Hoatson, R.L.Vold, J. Magn. Reson. 167 (2004) 242-252 and references therein]. The broad peak is resolved only at temperatures below the dielectric susceptibility maximum (i.e., T $<$T$_{c})$. This peak represents niobium ions in configurations that contain at least one other niobium in the shell of next nearest B-site neighbors. Decreasing temperature results in broadening of all lines, most notably the distribution peak; its line width increases by nearly a factor of two between 320 and 240 K. 3QMAS spectra show that the broadening of the distribution peak is mainly due to an increase in the distribution of quadrupolar parameters, resulting from asymmetric ion displacements and bond length variations. These changes occur continuously across the broad ferroelectric relaxor phase transition, and allow conclusions to be drawn regarding the chemical composition of polar nanoclusters. \newline \newline In collaboration with Gina Hoatson and Murugesan Vijayakumar, College of William \& Mary. [Preview Abstract] |
Thursday, November 9, 2006 9:00AM - 9:30AM |
BA.00002: Hydrogen Adsorption in Carbon-Based Materials Studied by NMR Invited Speaker: Hydrogen storage is a key component for hydrogen economy. So far, storage materials with large storage capacity and suitable adsorption energy remain elusive. The identification of future storage materials depends crucially on the understanding of adsorption mechanisms. Here we show that nuclear magnetic resonance (NMR) is a sensitive and quantitative probe for detecting adsorbed gas molecules (such as H$_{2}$, methane, and ethane) in carbon-based materials [1]. Adsorbed gas molecules can be identified through characteristic NMR signatures such as spectral lineshape and spin dynamics, which is determined by the distinct dynamic properties of the adsorbed molecules. NMR is shown to be valuable for the understanding of adsorption mechanisms. In our studies, NMR measurements were carried out in-situ under given H$_{2}$ pressure up to a pressure of over 100 atm. From such $^{1}$H NMR measurement, the amount of adsorbed H$_{2}$ molecules can be determined versus pressure. This gives an alternative method for measuring the adsorption isotherms where the H$_{2}$ signature is identified based on spin properties rather than weight or volume as in gravimetric and volumetric measurements. In addition, properties of molecular dynamics can be obtained at the same time providing information on the adsorption mechanisms. [1] A. Kleinhammes, S.-H. Mao, X.-J. Yang, X.-P. Tang, H. Shimoda, J. P. Lu, O. Zhou, and Y. Wu, \textit{Phys. Rev. B.} \textbf{68}, 075418 (2003). [Preview Abstract] |
Thursday, November 9, 2006 9:30AM - 10:00AM |
BA.00003: Advances to Enable $^{69,71}$Ga Nuclear Magnetic Resonance of Thin GaN Films Invited Speaker: High-field $^{69,71}$Ga Nuclear Magnetic Resonance (NMR) spectroscopy of GaN has recently been shown to be a valuable quantitative characterization technique sensitive to the presence of dopants and defects, polytypes, and distributions of carrier concentrations [1-3]. We report several new approaches that greatly improve the $^{69,71}$Ga detection sensitivity and have enabled study of single 3 $\mu $m thin films of GaN. NMR investigation of submicron films should now be feasible. \newline \newline \textbf{References} \newline [1] J.P. Yesinowski and A.P. Purdy, J. Amer. Chem. Soc., 126, 9166 (2004). \newline [2] J.P. Yesinowski: phys. status sol. (c), 2, 2399 (2005). \newline [3] J.P. Yesinowski, A.P. Purdy, H. Wu, M.G. Spencer, J. Hunting, F.J. DiSalvo: J. Amer. Chem. Soc., 128, 4952 (2006). [Preview Abstract] |
Thursday, November 9, 2006 10:00AM - 10:30AM |
BA.00004: Condensed Matter NMR under Extreme Conditions: Challenges and Opportunities Invited Speaker: Advances in resistive magnet and power supply technology have made available extremely high magnetic fields suitable for condensed matter broadline NMR experiments. This capability expands the available phase space for investigating a wide variety of materials using magnetic resonance; utilizing the strength of the field to expose or induce new physical phenomena resulting in better understanding of the physics. Continuous fields up to 45T in NHMFL Hybrid magnet have brought new challenges in designing NMR instrumentation. Field strengths and sample space limitations put constraints on RF pulse power, tuning range, bandwidth, and temperature control. The inclusion of other capabilities, including high pressure, optics, and sample rotation requires intricate probe design and construction, while extremely low milliKelvin temperatures are desired in order to explore energy scales where thermal fluctuations are suppressed. Optimization of these devices has been of paramount consideration in NHMFL Condensed Matter NMR user program. Science achieved at high fields, the new initiatives to develop resistively-detected NMR in 2D electron gas and similar systems, and the current new generation Series-Connected Hybrid magnets for NMR work will be discussed. The NHMFL is supported by the National Science Foundation and the State of Florida. [Preview Abstract] |
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