Study of protons in acceptor-doped KTaO 3 crystals by IR and EPR techniques

Abstract

In order to understand the manner of incorporation of protons into perovskite structure oxides, KTaO 3 crystals containing acceptor dopants Co 2+, Mn 2+, Cu 2+, and Fe 3+ were investigated following thermal treatments in various partial pressures of O 2 and H 2O. IR measurements were used to monitor the proton content through the OH − absorption bands, while quantitative EPR measurements were used to determine the changes in the local environment of the dopant ion. It is shown that the introduction of protons during high-temperature treatments in H 2O is accompanied by the replacement of the oxygen-ion vacancies ( V o) that initially compensated the acceptor dopants by O 2− ions. In the case of the M 2+ dopants, the dopant-vacancy association free energy is sufficiently strong to retain the M V O pairs even during high-temperature (900°C) treatments; thus, only 〈100〉 axial EPR spectra due to such pairs are observed. For Fe 3+ dopants, however, virtually all of the V o can be replaced by O 2−, leaving the Fe 3+ ion in a cubic environment. The results also show evidence for valence changes of the Co, Mn, and Cu dopants when treatments change from oxidizing to reducing atmospheres.