Fluoroargenate  Superconductivity

17 December, 2003
Courtesy:
Dr. Wojciech Grochala
Adjunct Associate,
Department of Chemistry
University of Warsaw
email: wg22@cornell.edu

     Fluoroargentates - higher silver fluorides and complex fluorides - have been theorized to be possible superconductor candidates because of their similarity to the oxocuprates (note above graphic). Now researchers Wojciech Grochalaa, b, Adrian Porchc and Peter P. Edwardsd report discovering sudden drops in magnetic susceptibility (Meissner-effect-like) within a large number of Be-Ag-F samples. They attribute this to possible spherical regions of superconductivity couched within a predominantly ferromagnetic(2) bulk. Equally surprising are critical transition temperatures up to 64 K !


     Normally if superconductivity were present in a material, it would be a simple matter to get confirmation by checking for a sudden drop in internal resistance, which shows up unambiguously even when the volume fraction is low. However, the fluoroargentates are highly reactive to air and moisture, and easily surface-reduced. As gold or platinum wires are attached, an insulating fluoride layer is formed, making validation very difficult. Further, a non-intrusive microwave cavity perturbation (MWCP) technique to measure conductivity has proven inconclusive.

     Efforts are now underway to develop both a non-contact method for measuring conductivity and a theoretical model to predict behavior within the AgF system - as well as to apply external pressure to higher fluorides of silver.

     UPDATE July 2008: Dr. Grochala has had second thoughts about drawing a conclusion of superconductivity for a minority phase embedded within a bulk simply from magnetic susceptibility readings. He states that this is tantamount to "searching [for] something amongst the weird noise...."

     NOTE: An updated technical paper on this discovery is available in SOLID STATE COMMUNICATIONS, 130(1): 137-142 2004.

     NOTE 2: From unreacted AgF2.





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