Role of oxygen vacancies on relaxation and conduction behavior of KNbO3 ceramic

Abstract

The temperature and frequency dependent dielectric and conductivity properties were measured on as-sintered as well as oxygen annealed KNbO3 ceramics. The results show that in addition to phase transition peaks, well defined relaxation peaks are observed in the temperature range 450–700 K. These peaks could be suppressed by annealing the samples in the oxygen atmosphere. The dc conductivity and maximum dielectric constant values decreases after oxygen annealing. Activation energy, calculated from dielectric relaxation and conductivity data on the samples, suggests that both the processes are due to doubly charged oxygen vacancies formed during sintering process. Dielectric relaxation is attributed to the hopping of oxygen vacancies in the six equivalent sites in perovskite structure. The dielectric and conductivity behaviors are influenced by the density of the samples. The results are explained on the basis of defect concentration and their dynamics.

Origin of colossal dielectric response in (In + Nb) co-doped TiO2 rutile ceramics: a potential electrothermal material

“…It is much smaller than the typical activation energy (~1000 meV) of ions, oxygen vacancies and/or dipoles in oxides. For instance, the activation energy of oxygen vacancies is 910 meV for BaTiO 3 22 , 1005–1560 meV for KNbO 3 30 , and 1030 meV for YBCO ceramics 31 . Liu et al .…”

Oxygen-vacancy-related relaxation and conduction behavior in (Pb1-xBax)(Zr0.95Ti0.05)O3 ceramics

“…29 It has been reported that the defects such as A-site vacancies, space charge electrons, 26 oxygen vacancies, 27 or other impurities are responsible for the dielectric relaxation in high temperature region.…”

“…Generally speaking dielectric relaxation due to interfacial polarization, space charge, domain wall motion, Maxwell-Wagner polarization, defect relaxation, and long-range structure disorder usually occurs at low frequency region, however, dipolar relaxation appears at higher frequency. 29,30 It is widely accepted that dielectric relaxation in dielectric materials in the temperature region above room temperature is usually related to OVs, and the hopping motions of singly/doubly-ionized OVs can lead to a relaxation processes in low-frequency region typically below mega hertz. 30,31 Thus, we consider that the relaxation observed in lower frequency spectrum should belong to space charge which may be due to oxygen vacancy and related defects.…”

“…It is widely accepted that dielectric relaxation induced by OVs should be quantitatively similar regardless of the kind of perovskite oxides due to the same relaxation mechanism. 23,29,30 It has also been reported that the short-range diffusion of oxygen ions/vacancies can lead to a dielectric relaxation with an activation energy around 1 eV, in which oxygen ions/vacancies act as polarons in perovskite oxides. 22,41 The high mobility of OVs in perovskite oxides is a well known fact.…”

The Effects of Mn Substitution and Oxidation States of Mn in BiFeO3Thin Films

“…Dielectric constant and dielectric loss increased with decreasing frequency, indicating high permittivity at low frequency is related to conductive properties. Dielectric relaxation observed in low frequency is attributed to space charges such as oxygen vacancies [6,7]. Thus the substitution of Mn 4+ decreases space charges while the substitution of Mn 2+ and Mn 3+ increases space charges [8].…”