  Weakly compacted fine particles of Ag4+xPb2O6-z which is iso-structural with
Bystroem-Evers oxide Ag5Pb2O6 exhibit a novel class of physical properties,
which includes an appearance of diamagnetism at t < 78 degrees Celsius, with
corresponding absence of electric resistance, both events sounding for possible
superconductivity. Weak compaction was performed by controlled pressing of
introductory components Ag2O and PbO2. Pellets were heated from room
temperature in an evacuated chamber, and solid state reaction proceeded at
340-350 degrees Celsius in an oxygen atmosphere released by reaction itself (60
< p < 100 mbar). Electric and magnetic properties appealing for an ambient
temperature superconductivity may be attributed to scattering processes
indicated by tunnelling of Ag-Ag clusters between states localized on the point
contacts formed between adjacent particles. As compared to the work on the
subject during past two decades, reproducibility of output data is
satisfactory, and their correlations to the input preparation conditions appear
as to be conclusive.
