Abstract:
It is well established that the properties of many materials change as their thickness is shrunk to the nanoscale, often yielding novel features at the near-surface region that are absent in the bulk. Even though there are several techniques that can study either the bulk or the surface of these materials, there are very few that can scan the near-surface region of crystals and thin films versus depth. Beta detected NMR (β-NMR) is capable of this and therefore has been established as a powerful tool for
material science.
This thesis aims to further develop the capabilities of β-NMR. By comparing the spin-lattice relaxation rates (SLR) of two radioactive Li isotopes (8;9Li) it is shown that it is possible to distinguish whether the source of SLR in a given situation is driven by magnetic or electric interactions. In addition, by coupling the β-decay signal with the subsequent α-decay of 8Li, a technique able to directly study nanometer-scale lithium diffusion was developed.
The first part of this thesis demonstrates that by studying a material with both 8;9Li-b-NMR, it is possible to distinguish the source of SLR. This is an important development for β-NMR, since there are instances where it is problematic to distinguish whether the measured relaxation is due to magnetic or electric fluctuations. Using this method, it was found that the SLR in Pt is (almost) purely magnetic in origin, whereas the spin relaxation in SrTiO3 is driven (almost) entirely by electric quadrupolar interactions.
The second part of this thesis traces the development of α-radiotracer, that uses the progeny α-particles from the decay of 8Li, in order to directly measure the nanoscale diffusivity of Li+ in Li-ion battery materials. To develop this technique, Monte Carlo simulations of the experimental configuration were carried out, a new apparatus and a new α-detector were designed and used for experiments on rutile TiO2. In rutile, the measurements revealed that Li+ gets trapped at the (001)
surface, a result that helps explain the suppressed intercalation of Li+ in bulk rutile. Moreover, the diffusion rate of Li+ in rutile was found to follow a bi-Arrhenius relationship, with a high-T activation energy in agreement with other reported measurements and a low-T component of similar magnitude with the theoretically calculated diffusion barrier as well as the activation energy of the Li-polaron complex found with β-NMR below 100 K.
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2020-01-31T12:30:002020-01-31T14:30:00"Diffusion and Trapping of 8Li in Rutile TiO2 and the Comparison of 8Li and 9Li Spin Relaxation Using Beta-NMR"Event Information:
Final PhD Oral Examination
Abstract:
It is well established that the properties of many materials change as their thickness is shrunk to the nanoscale, often yielding novel features at the near-surface region that are absent in the bulk. Even though there are several techniques that can study either the bulk or the surface of these materials, there are very few that can scan the near-surface region of crystals and thin films versus depth. Beta detected NMR (β-NMR) is capable of this and therefore has been established as a powerful tool for
material science.
This thesis aims to further develop the capabilities of β-NMR. By comparing the spin-lattice relaxation rates (SLR) of two radioactive Li isotopes (8;9Li) it is shown that it is possible to distinguish whether the source of SLR in a given situation is driven by magnetic or electric interactions. In addition, by coupling the β-decay signal with the subsequent α-decay of 8Li, a technique able to directly study nanometer-scale lithium diffusion was developed.
The first part of this thesis demonstrates that by studying a material with both 8;9Li-b-NMR, it is possible to distinguish the source of SLR. This is an important development for β-NMR, since there are instances where it is problematic to distinguish whether the measured relaxation is due to magnetic or electric fluctuations. Using this method, it was found that the SLR in Pt is (almost) purely magnetic in origin, whereas the spin relaxation in SrTiO3 is driven (almost) entirely by electric quadrupolar interactions.
The second part of this thesis traces the development of α-radiotracer, that uses the progeny α-particles from the decay of 8Li, in order to directly measure the nanoscale diffusivity of Li+ in Li-ion battery materials. To develop this technique, Monte Carlo simulations of the experimental configuration were carried out, a new apparatus and a new α-detector were designed and used for experiments on rutile TiO2. In rutile, the measurements revealed that Li+ gets trapped at the (001)
surface, a result that helps explain the suppressed intercalation of Li+ in bulk rutile. Moreover, the diffusion rate of Li+ in rutile was found to follow a bi-Arrhenius relationship, with a high-T activation energy in agreement with other reported measurements and a low-T component of similar magnitude with the theoretically calculated diffusion barrier as well as the activation energy of the Li-polaron complex found with β-NMR below 100 K.Event Location:
Room 203, Graduate Student Centre (6371 Crescent Road)