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The calculations of the electrical levels of the TM-H defects have allowed us to assign several observed levels to defects containing up to 3 H atoms. Whereas AuH3 and AgH3 may be passive, it seems that substitutional Pd and Pt cannot be inactivated by H. However, molecular hydrides of all the metal impurities are passive when inserted into microvoids. The calculations highlight several levels which remain to be detected, e.g. the (-/0) levels of AuH2, AgH2 and PtH. The observation of shallow donor levels E(90) and E(60) in Pt and Pd doped material respectively suggests to us that H does not simply aggregate around substitutional TM impurities.

Antonio Resende