From published patent WO 01/45138 A2, a method is known for producing a piezoelectric component that has internal electrodes made of copper. The component is produced by sintering in a sintering atmosphere that contains oxygen. The requisite oxygen partial pressure is set via a gas equilibrium that appears between the gases hydrogen and water vapor. Normally, ceramic materials based on lead zirconium titanate are used to produce a piezo actuator. In addition, retaining devices are used for holding a large number of unsintered components in a sintering furnace, which are made up of temperature-resistant structured ceramics, such as alumina, cordierite, silicon carbide, etc.
To prevent oxidation of the copper internal electrodes, it is necessary in the known method to set the oxygen partial pressure within a very narrow permissible pressure range. If the oxygen partial pressure is below this permissible level, the PZT ceramic is very easily reduced and thereby irreversibly damaged. If the permissible oxygen partial pressure is exceeded, this results in oxidation of and damage to the copper internal electrodes.
The known method has the disadvantage that the oxygen partial pressure set by the hydrogen/water vapor gas equilibrium can very easily be pushed outside of the permissible working range by very small quantities of oxygen-absorbing or oxygen-releasing substances. For example, substances such as residual carbon, impurities in the ceramic, or evaporation of lead from the ceramic can result in a shift in the oxygen partial pressure.
This can have the effect that even with the best possible setting of the gas atmosphere during sintering, local oxidation of the copper internal electrodes is observable. This manifests itself in intermediate layers or intermediate areas of copper oxide deposited between the internal electrodes and the ceramic material, which is macroscopically visible in the micrograph perpendicular to the internal electrodes. These intermediate layers of copper oxide cause degrading of the electrical properties of the piezoelectric component.
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