Spontaneous recovery of hydrogen-degraded TiO2 ceramic capacitors

Abstract

Degradation of TiO 2 -based ceramic capacitors was observed after hydrogen incorporation on the termination electrodes of the capacitors via electrolysis of water. Fourier-transform infrared ͑FTIR͒ absorption spectra analysis of polished rutile single crystals clearly showed that hydrogen was incorporated into the TiO 2 lattice through the treatment. Hydrogen reduces Ti 4ϩ to Ti 3ϩ and increases the concentration of charge carriers. The degradation was found to exhibit a strong dependence on time at room temperature. The degraded properties were spontaneously recovered through an aging process, showing a spontaneous recovery unique to TiO 2 -based ceramic capacitors. It is proposed that hydrogen is metastable in TiO 2 and that hydrogen-induced degradation has different stabilities among various oxide-based components and devices. © 2004 American Institute of Physics. ͓DOI: 10.1063/1.1637942͔The effects of hydrogen incorporation in materials have been extensively studied, particularly on metals ͑hydrogen embrittlement͒ and silicon-based devices ͑passivation of dangling bonds͒. In recent years, however, more and more attention has been paid to the reactions between hydrogen and metal oxide materials. [1][2][3] In our previous studies, we found that hydrogen reacts with many metal oxides at an ambient temperature in some electrochemical processes, including electroplating 4 and the electrolysis of water. 5,6 These ambient temperature reactions usually induce obvious degradations in the properties of these oxide-based components and devices. A systematic understanding of the reactions is of great importance for improving the reliability of metal oxide-based electronic components and devices. 7For many oxide-based components and devices, the degradation induced by the reaction of hydrogen is permanent and stable at room temperature. Sometimes, an annealing in an oxidizing atmosphere can recover the degraded properties. 4,8 Obviously, the hydrogen-induced defects in those oxides responsible for the degradation can only be eliminated by high-temperature oxidizing reactions. When we studied hydrogen-induced degradation in TiO 2 -based ceramic capacitors, however, we obtained a quite unexpected result. Although hydrogen induces an obvious degradation in the capacitors, the degraded properties exhibit a strong dependence on time, and the degradation is gradually recovered through an aging process without any thermal treatment. This indicates that hydrogen-induced defects are only metastable in TiO 2 -based ceramic capacitors at room temperature, in contrast to hydrogen-induced defects in many other oxides.The composition and sintering of the TiO 2 -based temperature-compensating ceramic capacitors used in the present investigation were reported in another paper. 9 The capacitors were 0.70 mm thick and 7.5 mm in diameter, with a 4.5 mm diameter silver electrode on one surface and a 5.5 mm diameter silver electrode on the other surface. Some capacitors were placed in a 0.01 M NaOH solution and dc voltages were imposed betwe...

Hydrogen: A metastable donor in TiO2 single crystals

“…In a previous investigation, hydrogen has been doped into TiO 2 single crystals through an electrochemical method. 9 Presently, a study on the behavior of hydrogen in TiO 2 single crystals has been conducted in terms of dielectric and conduction analyses, which strongly suggest that hydrogen acts a donor in TiO 2 while ionized hydrogen is not bound to an oxygen site by a strong O-H bond. Such behavior of hydrogen in oxides, which can be characterized as metastable donor, is different from the usual donor behavior of hydrogen in oxides and should help in understanding more fully the behavior of hydrogen in oxides.…”

Great diversity in stability of perovskite-type oxides studied by electrochemical hydrogen charging

“…A free electron was formed in the equation, which could well explain the increases in dielectric loss and in leakage current induced by the electrochemical hydrogen charging. As we had pointed out for TiO 2 [2] , hydrogen was only metastable in SrTiO 3 lattice. The properties of SrTiO 3 could be mostly recovered through an aging process during which hydrogen gradually diffused out of the lattice.…”

“…On the other hand, ceramic components and devices always operate under some voltages, which could electrolyze water condensed from ambient environment. It has been proposed that the reduction of hydrogen from the electrolysis of water is an important degradation origin for ceramic components and devices in service [2,3] .…”

Hydrogen-induced degradation in CaCu3Ti4O12 ceramics

“…As we proposed in some previous researches [8,10], hydrogen atoms deposited on silver electrodes may diffuse into ceramics and react with them at room-temperature, though most of them combine with one another and form hydrogen molecules. The properties of the ceramics are usually greatly changed by the reaction of hydrogen, the same as the properties of the CCTO ceramics in this study.…”