dc.contributor.author | Miller, Kimberly J | |
dc.date.accessioned | 2012-12-13T14:50:05Z | |
dc.date.available | 2012-12-13T14:50:05Z | |
dc.date.issued | 2012-12-13 | |
dc.identifier.uri | http://hdl.handle.net/10222/15817 | |
dc.description.abstract | The A2Mo3O12 family, where A3+ is a large trivalent cation, can show interesting thermal properties such as negative thermal expansion, also known as thermomiotic behavior, where the overall volume of the material contracts with increasing temperature. A selection of compounds in this family, namely HfMgMo3O12, In2Mo3O12, Y2Mo3O12, Al2Mo3O12, In(HfMg)0.5Mo3O12, and In1.5(HfMg)0.25Mo3O12, have been synthesized using solid-state and mechanical activation techniques as well as a simplified sol-gel approach (Al2Mo3O12). Coefficients of thermal expansion were found to range from large-negative to low-positive in the orthorhombic phase, including near-zero in In(HfMg)0.5Mo3O12 and In1.5(HfMg)0.25Mo3O12. This set of materials provided insight into the role of low-frequency phonon modes in open-framework materials. Low-temperature heat capacity and thermal conductivity measurements confirmed that low-frequency modes were active in thermomiotic materials, and also present to some extent in all members of the open-framework A2Mo3O12 family examined. A clear correlation exists between the magnitude and sign of the coefficient of thermal expansion in the orthorhombic phase and the contribution of low-energy modes to the low-temperature heat capacity, with negative thermal expansion materials having a larger contribution. The low-frequency phonon modes result in low thermal conductivity and reduced phonon mean free paths when compared to conventional ceramics and indicate that these low values are characteristic of open-framework materials in NTE families even if the materials in the families are not thermomiotic themselves. | en_US |
dc.language.iso | en | en_US |
dc.subject | thermal expansion | en_US |
dc.subject | thermal conductivity | en_US |
dc.subject | thermomiotic | en_US |
dc.subject | negative thermal expansion | en_US |
dc.subject | ceramics | en_US |
dc.subject | heat capacity | en_US |
dc.subject | NTE | en_US |
dc.title | Towards Near-Zero Coefficients of Thermal Expansion in A2Mo3O12 Materials | en_US |
dc.date.defence | 2012-12-06 | |
dc.contributor.department | Department of Chemistry | en_US |
dc.contributor.degree | Doctor of Philosophy | en_US |
dc.contributor.external-examiner | Dr. Cora Lind-Kovacs | en_US |
dc.contributor.graduate-coordinator | Dr. Mark Stradiotto | en_US |
dc.contributor.thesis-reader | Dr. Josef Zwanziger | en_US |
dc.contributor.thesis-reader | Dr. Peng Zhang | en_US |
dc.contributor.thesis-reader | Dr. Jeff Dahn | en_US |
dc.contributor.thesis-supervisor | Dr. Mary Anne White | en_US |
dc.contributor.ethics-approval | Not Applicable | en_US |
dc.contributor.manuscripts | Not Applicable | en_US |
dc.contributor.copyright-release | Yes | en_US |