Low temperature synthesis and characterization of some low positive and negative thermal expansion materials.

摘要

Low temperature non-hydrolytic sol-gel synthesis was used to explore the possibility of lowering the crystallization temperatures of some known AIVMV2O7 compounds. Crystallization temperatures for ZrP2O7 and ZrP2O7 were unaffected by the use of non-hydrolytic sol-gel methods; however, successful synthesis of these compounds broadens the range of materials that can be produced using this method and suggests the possibility of synthesizing solid solutions (or composites) including ZrP2O7 or ZrV2O 7.; This research presents for the first time the direct synthesis of ZrP 2O7 from separate zirconium and phosphorus starting materials using mild autoclave methods.; Characterization of some AIVMV2O 7 compounds, using lab and high resolution synchrotron powder XRD, led to the assignment of a new symmetry for CeP2O7 and to the suggestion that the reported structure for PbP2O7 was inadequate. Studies using in situ high temperature lab and synchrotron powder XRD for PbP2O7 and CeP2 O7 provided the opportunity to report their thermal properties for the first time, and to compare their behavior to that of some other A IVMV2O7. High pressure diffraction measurements an CeP2O7 provided data for the estimation of bulk moduli and suggested two possible pressure-induced phase transitions.; A broad range of MIIIM'VP4O 14 compounds were prepared using low temperature hydrolytic sol-gel synthesis. Thermal studies revealed nearly linear trends in CTEs and lattice constants with respect to the sizes of MIIIM'V cations. Some lower ionic radii compounds had CTEs comparable to that of ZrP 2O7 at low temperature, suggesting a similar superstructure. Three compounds were found to exhibit temperature-induced phase transitions.