Growth by plasma electrolysis of zirconium oxide films in the micrometer range

The growth of thick films of zirconium oxide in the micrometer range by high voltage anodisation in 0.1M (NH4)2B4O7 is investigated. The impedance spectra reveal a bi-layer structure above 50 V. Another transition is observed at around 440 V with the occurrence of electrical discharges: the anodic process gives the way to plasma electrolysis. The growth has been continued up to an arbitrarily fixed maximum potential of 600 V. Plasma electrolysis gives rise to macroporous, uneven and well-crystallised films of monoclinic zirconia with a 3.2 μm thickness at 580 V. The surface presents singular “volcano-like” structures centered on a pinhole and the whole surface is progressively fully covered by these structures when the voltage sweep goes on. This is accompanied by an acceleration of the growth rate.