Both natural minerals and synthetic materials used in chemistry, materials science, ceramics, and electronics are characterized by specific crystal structures: three-dimensional, periodically repetitive arrangements of atoms in space. Glasses and liquids have local ordering of atoms, often similar to that in crystals but lacking the long-range periodicity. The questions central to our research are: Why do these specific structures form, and how stable are they with respect to other structures that might form, for example, under different conditions of pressure, temperature, and overall chemical composition?

The goal is to relate thermodynamic properties (which measure stability) to structure (arrangement of atoms) and chemical bonding (studied both by theoretical and experimental methods). Understanding these relations in turn facilitates the prediction of properties (electronic states, color, magnetic behavior, mechanical behavior, corrosion resistance at high temperature, to name a few examples) that are important to practical applications.

In the depths of the earth, minerals existing near the surface in well-known, relatively open crystal structures transform to phases of much high density. Such materials (for example, magnesium silicates in the olivine, modified spinel, spinel, pyroxene, ilmenite, garnet, and perovskite structures) are studied by solution calorimetry to obtain their energies. High pressure hydrous phases are also being studied. High pressure water-containing phases are also of interest. This work is part of CHiPR, the Center for High Pressure Research, an NSF Science and Technology Center which links Davis, the State University of New York at Stony Brook, and the Geophysical Laboratory of the Carnegie Institution of Washington.

Perovskite related materials with transition metals in high formal oxidation states (e.g. Cu3+, Ni3+, Co4+, Mn4+) are important as catalysts, superconductors, battery materials, and electronic ceramics. After completion of a very successful 6-year study the thermodynamics of high Tc oxide superconductors, the group has moved on to studies of the broader range of variable oxidation state oxides, with current emphasis on stable and metastable manganese oxides and on rare earth perovskites of cobalt and manganese, including those showing giant magnetoresistive effects.

Silicate, aluminosilicate, and borosilicate glasses and melts are important both as technological materials (window and container glass; coatings on metals, ceramics, and semiconductors; and possible nuclear waste containment material) and as geologic materials (magmas). Our group is studying their thermodynamic properties and relating them to structure, physical properties, and crystallization of various minerals from such silicate melts. The systems studied range from very simple ones, chosen because they illustrate changes in structure and chemical bonding, to systems that model geologic processes (the formation of basalts and granites), to doped silica systems encountered in the semiconductor and optical communications industry.

The thermodynamics of nitrides and oxynitrides represents a virtually unexplored field. Such materials are increasingly important as modern ceramics for high temperature applications requiring high strength and low reactivity. Several members of our group are developing calorimetric methodology for sialons (ceramics containing Si, Al, O, N), for zirconium and titanium nitrides, and for ternary transition metal nitrides.

Metastable phases, high surface area and nanophase materials, and microporous materials (e.g. zeolites) play an increasingly important role in ceramic processing and in the tailoring of new catalysts and other chemically active solids. Several projects explore the relation of energetics, structure, and surface area. A multifaceted project on zeolites, involving natural minerals, synthetic SiO2 and AlPO4 polymorphs, and synthetic aluminosilicates tailored for specific industrial applications receives support from both government and industry. Work on nanocrystalline alumina, magnesium aluminate, and other ceramics is also underway. These studies shed new light on the continuous change between crystalline and amorphous (and glassy) states and on the influence of short, medium, and long-range order on structure and stability. This work is part of a new Davis initiative on Nanophases in the Environment, Agriculture, and Technology (NEAT) and of a submitted Materials Research Science and Engineering Center (MRSEC) NSF proposal.

The disposal of weapons grade plutonium and other actinides by immobilization in ceramic wasteforms is being explored by the Department of Energy. The thermodynamics of these phases is being studied under a collaborative project between our group, Livermore National Laboratory, and Los Alamos National Laboratory.