Date of Award
Doctor of Philosophy (PhD)
Kolis, Joseph W
Ballato , John
Pennington , William
Chumanov , George
Over the past two hundred years synthetic growth of crystals has become vital to the technological advancement of our society. A variety of crystal growth techniques have been developed during this time, with each having its own nuances. These differences have enabled the growth of a wide spectrum of crystalline materials that can be used for many applications which include solid state lasers, semiconductors, and communication devices. Despite these techniques there are entire classes of materials which have thus far proved quite difficult to prepare as single crystals. In particular, crystal growth of the tetravalent and pentavalent metal oxides has been a great challenge due to their high melting points. The extreme temperatures (2000-3400oC) needed to melt many of these materials have proved difficult for the classical melt based techniques. This dissertation utilizes the hydrothermal technique to provide a low temperature synthesis alternative to access single crystals of the tetravalent and pentavalent metal oxides.
The materials that were explored can be characterized into three categories which include applications in the fields of nonlinear optics, dielectrics, and refractory oxides. This study initially began with the growth of the nonlinear materials fresnoite, Ba2TiOSi2O7, and KNbO3. While not extremely high melting members of the tetravalent and pentavalent metal oxides, growth of these materials at relatively low temperatures established a sound basis to proceed with the exploration of the refractory oxides. These included the monoclinic and stabilized cubic form of ZrO2 and HfO2 as well as ThO2. It was quickly discovered that these materials required higher synthesis temperatures than previously employed in this lab. However after a redesign of the heating system, hydrothermal growth of these materials was achieved at 750oC, which is still relatively low compared to their synthesis by other techniques.
The new temperature regime also enabled the exploration of the Group IV transition metal perovskites structures with their high melting points and exceptional dielectric properties. With successes in these areas, basic exploratory work of the tetravalent and pentavalent metals provided many novel structures of alkali thorium silicates and barium titanium tantalates. The formation of these novel materials and the crystallization of the refractory oxides in this work demonstrate the versatility of the hydrothermal technique.
Mann, James, "Hydrothermal Crystal Growth of Tetravalent and Pentavalent Metal Oxides" (2009). All Dissertations. 394.