Dielectric Relaxations in Rutile TiO₂

Abstract

Dielectric properties of high-purity (4N degree) rutile TiO 2 ceramics were investigated over a wide temperature (100-1073 K) and frequency (20 Hz-10 MHz) ranges. X-ray photoemission spectroscopy measurement revealed the sample possesses mixed-valent states of Ti 3+ /Ti 4+ . Four thermally activated relaxations were observed. The lowest temperature relaxation (R1) features two Arrhenius segments with activation energy of 30 and 80 meV for the low-and high-temperature segments, respectively. This relaxation was argued to be a polaron relaxation due to electrons hopping between Ti 3+ and Ti 4+ ions. The second relaxation (R2) appears around room temperature showing activation energy of 0.68 eV is believed to be a Maxwell-Wagner relaxation. The high-temperature relaxations R3 and R4 with activation energy of 0.84 and 1.26 eV were ascribed to the conduction process due to the hopping motions of singly and doubly charged oxygen vacancies, respectively. N. Alford-contributing editor Manuscript No. 34785.

Colossal permittivity behavior and its origin in rutile (Mg1/3Ta2/3)xTi1-xO2

“…Again, similar relaxation has been observed in Ga + Nb co-doped rutile TiO 2 and more strongly in Ta-only doped rutile TiO 2 (Figure S6), and originates from Ti 3+ -related polaron-like structures. For these relaxations electrons are trapped by the distorted lattice structure giving local polarization relaxation behavior in the low temperature range, as experimentally observed in reduced rutile TiO 2 27 , and theoretically demonstrated in Nb-only and Ta-only doped rutile TiO 2 28 . The relaxation appearing at ~160 K-330 K exhibits obvious relaxation peaks in both the permittivity and dielectric loss spectra, a typical relaxor type relaxation behavior (as magnified in Figure S7), which is also observed in the same temperature range in M  + Nb co-doped rutile TiO 2 ( M  = In, Ga) 1, 14 as well as In + Ta co-doped rutile TiO 2 4 .…”

“…The different dielectric behaviors are at least partially related to different preparation processes, including the temperature and atmosphere used for synthesis, which is intimately related to defect structures such as the oxygen vacancies and reduction of Ti 4+ into Ti 3+ . It is noteworthy that rutile TiO 2 itself under certain process conditions exhibits the reduction of Ti 4+ into Ti 3+ , resulting in delocalized electrons which give BLC effects with a considerably increased dielectric loss 27 . Therefore, it is imperative to continue to systematically investigate different EPDDs formed in different co-doping ion combinations and host materials, advancing the understanding of defect chemistry in solids.…”

Colossal permittivity in ceramics of TiO2Co-doped with niobium and trivalent cation

“…5(a). 32 These results taken together indicate that compared to the dielectric properties of pure TiO 2 , the dielectric properties of the doped ceramics of this work are relatively stable over a wide temperature range, and are best for the ceramics with x ¼ 0.5%. Furthermore, a regional element mapping was carried out, as shown in Fig.…”

Colossal permittivity properties of Zn,Nb co-doped TiO2with different phase structures

“…Fig. 27 Since the hopping motions of localized carriers yield bulk dielectric response, the spectroscopic plot of dielectric loss is expected to be independent of d.c. bias. Both the dielectric permittivity and loss increase with the increase of the applied dc bias, particularly at low frequency.…”