Electrical properties of rutile-type In(Al) ^sub 0.025^Nb ^sub 0.025^Ti ^sub 0.95^O2 ceramics

We determined a series of electrical quantities on rutile-type In ^sub 0.025^Nb ^sub 0.025^Ti ^sub 0.95^O2 (INT005) and Al ^sub 0.025^Nb ^sub 0.025^Ti ^sub 0.95^ O ^sub 2^ (ANT005) ceramics in an attempt to analyse in particular the premises for formation of high dielectric constant [epsilon](ω) (ω is angular frequency = 2 πf) and low dielectric dissipation factor tan δ over broad temperature and frequency ranges, observed recently on compositions of rutile-type In ^sub x/2^Nb ^sub x/2^Ti ^sub 1-x^O2 (0 ≤ × ≤ 0.1) (INT) ceramics. The values of these quantities are thought to be determined by a mechanism termed electron-pinned defect dipole clusters. The detailed conditions for formation of this special kind of clusters, including the presence of oxygen vacancies and Ti ^sup 3+^ cations, are evidently unknown yet. We used a changed processing method of sample preparation in air relative to that applied in the literature. The observed different experimental results might supply information on the different microstructure of the oxides. For both oxides prepared in air, [epsilon](ω) is rather low with values < ~40 at room temperature (RT) in the frequency range of 162 Hz to 6 kHz and tan δ < 1. With rising temperature, [epsilon](ω) increases more and more up to the maximum applied temperature of ~750 K, reaching values of [epsilon](ω) ~10 ^sup 4^ (162 Hz), 4 ×10 ^sup 2^ (6 kHz) and tan δ ~35. The electrical DC conductivity σ ^sub D C^ of the bulk is low and exhibits Arrhenius behaviour marked by activation energy for INT005 of E ^sub A^=0.77 eV and σ ^sub D C^(500 K) ~2 ×10 ^sup -6^ Ω^sup -1^ cm ^sup -1^, for ANT005 it is E ^sub A^=0.85 eV and σ ^sub D C^(500 K) ~2 ×10 ^sup -5^ Ω^sup -1^ cm ^sup -1^. The frequency dependence of AC conductivity σ ^sub A C^(ω) is rather reduced for both oxides, no UDR power law dependence can be determined as a consequence of superposition of bulk and grain boundary contributions. The low [epsilon](ω) values, compared to literature data of >10^sup 4^ at RT, supply evidence of a critical dependence on sample processing conditions. We suspect important factors may be the concentration of oxygen vacancies and possibly non random distribution of cations. We varied our preparation conditions, using also less oxidizing atmosphere of CO2, that resulted for INT005 in enhanced σ ^sub D C^(500 K) ~10 ^sup -3^ Ω^sup -1^ cm ^sup -1^ and Arrhenius behaviour with E ^sub A^ ~0.6 eV and also low [epsilon](ω) at RT; similar values were observed