Microwave Dielectric Loss of Titanium Oxide

The dielectric loss (tan δ) of titanium dioxide (TiO₂) disks has been measured at a frequency of 3 GHz. High-purity TiO₂ sintered to almost-full density exhibits a very high tan δ, which is interpreted to be due to oxygen deficiency. To counter this, doping with stable divalent and trivalent cations, such as Mg and Al, leads to a low tan δ, probably by preventing Ti⁴⁺ reduction. The tan δ of polycrystalline TiO₂ doped with divalent and trivalent ions with ionic radii in the range of 0.5–0.95 Å at 3 GHz can be very low: 6 × 10⁻⁵ ( Q ∼ 17 000) at a temperature of 300 K. The tan δ of undoped pure TiO₂ disks increases when the disks are cooled from 300 K to ∼100 K. At temperatures <100 K, the tan δ decreases rapidly, which is interpreted as carrier freeze-out. The tan δ for all the high- Q doped TiO₂ polycrystalline samples smoothly decrease to ∼5 × 10⁻⁶ ( Q ∼ 200 000) at 15 K, comparable to that of single crystals.