Commercial-Scale Synthesis of p-type Transparent Conductors (21006
A new process affording a single step route to polycrystalline samples of any delafossite-like (ABO2) material with phase purity has been developed. These materials exhibit luminescence, catalysis, and p-type conducting properties. These materials can be employed as sputtering targets in thin film fabrication, p-type transparent conducting oxides (TCOs), and in opto-electronic and photo-voltaic applications.
ADVANTAGES: The synthesis of solid solutions, previously unattainable via other synthetic methods, can now be realized. A single general reaction scheme for preparing any delafossite-like (ABO2) material illustrates the flexibility and simplicity of this technology. This invention does not require special facilities and is compatible with commercial-scale hydrothermal equipment
SUMMARY: Currently, a practical and efficient commercial-scale method for the direct synthesis of phase pure polycrystalline delafossite-like (ABO2) materials does not exist. Such materials are well known for their luminescence properties and applications in chemical and electro-catalysis, and have recently become the subject of considerable interest for use as p-type transparent conducting oxides. Current preparative methods (traditional solid-state ceramic and high-pressure hydrothermal syntheses) require reaction conditions and durations that are not conducive to commercial manufacture and are limited by their failure to yield a pure single product.
This invention successfully overcomes the deficiencies of prior methods by providing a single step, low temperature and pressure; hydrothermal route whereby polycrystalline samples of any delafossite-like material can be fabricated with phase purity. The overall process lends itself well to automation by eliminating regrinding or purification steps used in prior procedures. Each delafossite-like material is produced according to one universal reaction scheme, which incorporates a redox step that facilitates dissolution of the key difficultly soluble species. The redox chemistry employed is essential to phase purity. These polycrystalline materials exhibit superior conductivity and thermal stability compared to their bulk solid-state-synthesized counterparts. Optical and electrical properties can be tailored through the incorporation of isovalent and aliovalent cation substitution.
Various samples of copper delafossites (CuMO2, where M=Al, Ga, Fe, and La) have been produced. The complete CuAl1-xGaxO2 solid solution has also been synthesized. The intercalation of a large amounts of oxygen, resulting from aliovalent cation substitution of the CuAlO2 parent, yields an unusually high hole carrier doping level of p=0.24, which is believed to be responsible for superior product conductivity. Further, A- and B-cation combinations are being investigated for improved transparency and p-type conductivity. (Chem. 2001, 40, 5734)
STATUS: U. S. Patent No. 6,979,435 has issued
Dean Y. Shahriari, Antoine Barnabé, Thomas O. Mason and Kenneth R. Poeppelmeier
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