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dc.contributor.authorVarga, Tamasen_US
dc.date.accessioned2005-07-28T17:59:41Z
dc.date.available2005-07-28T17:59:41Z
dc.date.issued2005-04-27en_US
dc.identifier.urihttp://hdl.handle.net/1853/6905
dc.description.abstractSynthesis and Characterization of Some Low and Negative Thermal Expansion Materials Tamas Varga 370 pages Directed by Dr. Angus P. Wilkinson The high-pressure behavior of several negative thermal expansion materials was studied by different methods. In-situ high-pressure x-ray and neutron diffraction studies on several compounds of the orthorhombic Sc2W3O12 structure revealed an unusual bulk modulus collapse at the orthorhombic to monoclinic phase transition. In some members of the A2M3O12 family, a second phase transition and/or pressure-induced amorphization were also seen at higher pressure. The mechanism for volume contraction on compression is different from that on heating. A combined in-situ high pressure x-ray diffraction and absorption spectroscopic study has been carried out for the first time. The pressure-induced amorphization in cubic ZrW2O8 and ZrMo2O8 was studied by following the changes in the local coordination environments of the metals. A significant change in the average tungsten coordination was found in ZrW2O8, and a less pronounced change in the molybdenum coordination in ZrMo2O8 on amorphization. A kinetically frustrated phase transition to a high-pressure crystalline phase or a kinetically hindered decomposition, are likely driving forces of the amorphization. A complementary ex-situ study confirmed the greater distortion of the framework tetrahedra in ZrW2O8, and revealed a similar distortion of the octahedra in both compounds. The possibility of stabilizing the low thermal expansion high-temperature structure in AM2O7 compounds to lower temperatures through stuffing of ZrP2O7 was explored. Although the phase transition temperature was suppressed in MIxZr1-xMIIIxP2O7 compositions, the chemical modification employed was not successful in stabilizing the high-temperature structure to around room temperature. An attempt has been made to control the thermal expansion properties in materials of the (MIII0.5MV0.5)P2O7-type through the choice of the metal cations and through manipulating the ordering of the cations by different heat treatment conditions. Although controlled heat treatment resulted in only short-range cation ordering, the choice of the MIII cation had a marked effect on the thermal expansion behavior of the materials. Different grades of fluorinert were examined as pressure-transmitting media for high-pressure diffraction studies. All of the fluorinerts studied became nonhydrostatic at relatively low pressures (~1 GPa).en_US
dc.format.extent6409633 bytes
dc.format.mimetypeapplication/pdf
dc.language.isoen_US
dc.publisherGeorgia Institute of Technologyen_US
dc.subjectNegative thermal expansionen_US
dc.subjectHigh pressure
dc.subjectX-ray diffraction
dc.subjectX-ray absorption spectroscopy
dc.subjectPressure-induced amorphization
dc.subjectThermal behavior
dc.subject.lcshExpansion (Heat)en_US
dc.subject.lcshMaterials Thermal propertiesen_US
dc.subject.lcshCationsen_US
dc.titleSynthesis and Characterization of Some Low and Negative Thermal Expansion Materialsen_US
dc.typeDissertationen_US
dc.description.degreePh.D.en_US
dc.contributor.departmentChemistry and Biochemistryen_US
dc.description.advisorCommittee Chair: Dr. Angus P. Wilkinson; Committee Member: Dr. Jiri Janata; Committee Member: Dr. L. Andrew Lyon; Committee Member: Dr. Meilin Liu; Committee Member: Dr. Z. John Zhangen_US


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