Ferroelectric compounds having the reticular structure - of perovskite and stable electrical properties

摘要

Electrical ageing of a tetragonal and ferroelectric crystalline structure of high purity barium titanate is slowed down by a method of production which reduces its affinity for the reabsorption of oxygen ions into the mesh structure in which the barium ions occupy the corners, the titanium ions the centre, and the oxygen ions the centres of the faces. Solution of barium and titanium are caused to react to precipitate a complex salt which is filtered and dried and then heated to obtain the perovskite mesh structure, which is stabilized by substitution for a minor proportion of the titanium ions, of manganese ions which are capable of existing in several stable states of oxidization within the mesh structure whilst preserving an ionic beam almost equal to that of the titanium ions. The proportion of manganese is of the order of 1 to 100 moles per million moles, and the inclusion of ionic impurities in the mesh structure is limited to 100 moles per million including the manganese ions of subtitution; the titanium ions and the manganese ions of substitution are held in a stoichiometric accord with the barium ions of about 1.02:1 to 1:1 so that they are thus in excess. The maximum temperature of the precipitate is limited to 700 degrees C during the heating which confers the mesh structure, then one expels a certain number of oxygen ions from the mesh structure by fritting in an oxidizing atmosphere at a temperature of about 900 to 1390 degrees C in order to liberate electrons coming from the oxygen ions so that they yield atomic oxygen, except that the freed electrons are captured by the manganese ions, and one continues the fritting until one obtains on cooling to ambient temperature the product sought.