For storing charge, US researchers have reported the highest known breakdown strength for bulk glass.
"Breakdown strengths for bulk glasses are typically in the 4-9MV/cm range. The breakdown strength for the tested samples were in the 12MV/cm range," claimed Penn State University which made the measurement.
Taking into account its permittivity, this gives the glass a storage potential of 35J/cm3, said the University, compared to a maximum energy density of 10J/cm3 for the polypropylene commonly used for pulsed power applications.
"For a bulk glass, this is extraordinary," said researcher Nick Smith who used 50µm thick samples of commercial alkali-free barium boroaluminosilicate glass, which he etched to 10-20µm with hydrofluoric acid.
This is produced in large quantities for flat panel displays and chip electronics packaging.
"Its energy storage capability is attributed to the highly polarisable barium atoms which contribute to the enhanced permittivity, and the alkali-free composition which inhibits energy loss," said Penn State, adding that the way it is made also means it is nearly defect-free.
"This opens a potentially new market for glass," said Smith. "We are always looking for new functionalities in glass."
The university pointed out a potential problem: "Engineering challenges remain as they scale up from the small size glass capacitors tested to those ready for commercial production. We'll lose some of the energy density as we increase in volume, but we should still end up with some remarkable capacitance."
'Glass as a high energy density dielectric material,' is a paper in the June 2009 edition of Materials Letters.
Alkali-free barium boroaluminosilicate glass, made visible with a coating of platinum