Microwave Dielectric Loss of Titanium Oxide

Abstract

The dielectric loss (tan δ) of titanium dioxide (TiO 2 ) disks has been measured at a frequency of 3 GHz. High‐purity TiO 2 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 Ti 4+ reduction. The tan δ of polycrystalline TiO 2 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 TiO 2 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 TiO 2 polycrystalline samples smoothly decrease to ∼5 × 10 −6 ( Q ∼ 200 000) at 15 K, comparable to that of single crystals.