Detlev Dr. Hennings

Donor-Acceptor Charge Complex Formation in Barium Titanate Ceramics: Role of Firing Atmosphere

BaTiO3 ceramics containing Mn acceptors and various Mo, W and Nb donor dopants have been fired in reducing atmosphere and re-oxidized in N2/O2. In single Mn-doped ceramics, Mn2+ is completely oxidized to Mn3+; in N2 containing 50 ppm O2 at T > 800°C. Changes of the Curie point and sample length under reduction and re-oxidation have been detected using dielectric and thermomechanical measurements. Charge compensation and complex formation between acceptors and donors have been observed. In donor-acceptor charge complexes, Mn2+ cannot be oxidized.

DIELECTRIC PROPERTIES OF ACCEPTOR-DOPED (BA, CA)(TI, ZR)O3 CERAMICS

The dielectric properties of (Ba,Ca)(Ti,Zr)O3 ceramics containing various acceptor and donor dopants on the B sites have been studied. Formation of charge compensating “complexes” between acceptors, donors and oxygen vacancies has been observed. All acceptors cause a reduction of the Curie point. The maximum dielectric constant increases with the average grain size almost independent of the acceptor incorporated. Ceramics fired in reducive atmospheres reveal pronounced changes of the dielectric properties after annealing in oxidizing atmosphere. In particular the losses and the maximum dielectric constants are significantly affected by the annealing time, temperature and partial pressure of oxygen.