High Temperature Hydro Thermal Synthesis and Crystal Growth of Inorganic Oxides

Clemson University, Clemson SC

Investigators

Abstract

TECHNICAL SUMMARY: This new proposal outlines plans to exploit the hydrothermal method to explore new categories of materials with particular emphasis on extremely refractory oxides. The hydrothermal method employs water at extremely high temperatures and pressures and has proven to be an excellent technique for the preparation of a wide variety of inorganic materials as high quality single crystals. Technology was developed at Clemson to do reactions at substantially higher temperatures (750¢ªC) with more powerful and concentrated mineralizers (e.g.>25M hydroxide or halide) than any previously work in these labs. These conditions enable synthesis and good crystal growth on chemical systems heretofore too inert or refractory to be otherwise accessible. The specific categories of solids to be investigated are; 1) wide bandgap oxides, specifically the s block metal borates and beryllates; 2) ultrarefractory oxides like hafnates, thorates and yttrates; and 3) large single crystal ferromagnetic oxides for neutron diffraction study. The fundamental reaction chemistry will be systematically explored for each class of materials. Single crystals will be targeted in all cases. Our crystal growth can be divided into three broad regimes, namely crystals large enough for single crystal diffraction (0.3mm), crystals large enough for single crystal magnetic and piezoelectric characterization (1-2mm), and crystals large enough for optical device characterization (1cm). Each of these size regimes will employ an appropriate hydrothermal growth method. For example, for wide bandgap oxides to find use in deep UV optical applications, single crystals of 1 cm/edge will be required for characterization in prototype optical devices. In contrast, ferrimagnets specifically grown for single crystal magnetic structures on the nearby Oak Ridge Spallation Neutron Source will require single crystal 1-2 mm per edge. NON-TECHNICAL SUMMARY: This work will employ a relatively obscure technology to grow single crystals of solids that are otherwise difficult to study. The solid crystals will have applications in many advanced technologies, especially lasers, advanced optics, magnetic materials and sensors. The field of crystal growth has all but disappeared from university research programs in the United States. This shortcoming has created a major gap in the skill set of onshore materials science capabilities. There is substantial evidence that this shortcoming is having a significant impact on national competitiveness in key materials. Furthermore this shortcoming has a significant negative impact on the students¡¯ research abilities. This is detrimental to scientific research and discouraging to students. A rational and systematic ability to grow crystals of sufficient size and quality for physical property evaluation leads to a dramatic improvement in the breadth of student development. Often patents result from this work and the resultant commercial application provides an important perspective to the students who are much thus better prepared to make better decisions about experimental design. Finally the technology is very ¡°green¡±, which raises the awareness of the students to societal impact of their science.