Alexandra Navrotsky

University of California, Davis

Election Year: 1993
Primary Section: 15, Geology
Secondary Section: 33, Applied Physical Sciences
Membership Type: Member

Research Interests

My research interests are in solid-state chemistry, ceramics, and the physics and chemistry of minerals. The basic questions my research seeks to answer are: Why is a given structure stable? Why is that arrangement of atoms in a solid and not some other state? My main research tool is high-temperature calorimetry, the measurement of enthalpies of formation, melting, and phase transition by state-of-the art custom built instrumentation. The thermochemical data are used in conjunction with structural and spectroscopic data. The results relate a microscopic picture of bonding in the solid state to macroscopic properties. The interrelationships among energetics, structure, and oxidation state in phases related to oxide superconductors is a major area of study. Emphasis is on structures related to perovskite and dipotassium nickel tetraflouride types. We are extending our studies from superconductors which contain copper in nominal high oxidation states to oxide fuel cell materials which are perovskites with high oxidation states of Mn, Fe, Co, and Ni. High-pressure phase transitions, particularly those involving changes in local coordination in oxides and silicates of both geophysical and ceramic interest, are studied by calorimetry. Development of new, more sensitive techniques for very small samples is being done in the NSF Science and Technology Center for High Pressure Research. Melting and crystallization involving both glasses and silicate liquids are being studied by in situ calorimetric techniques up to 1,500 degrees Celsius. Nonquenchable transitions in ceramics, involving both order/disorder and symmetry change are also being studied by scanning calorimetry at high temperatures. These studies are important to understanding the temperature behavior of minerals, ceramics, glass-melts, and magmas. The chemical and thermal evolution of silica-based gels on heating-and its dependence on and alumina-gelation conditions, atmosphere, and processing additives is another area of interest. Zeolites, whose open frameworks provide a variety of structures and ionic substitutions, are important as molecular sieves, catalysts, and minerals. We are studying their basic energetic relationships. A new area is the thermochemistry of nitrides, about which very little is currently known. Calorimetric methodology is being developed for these materials, some of which are refractory and others very air-sensitive.

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