Microwave dielectric loss of titanium oxide

The dielectric loss (tan delta) 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 delta, 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 delta, probably by preventing Ti4+ reduction. The tan delta of polycrystalline TiO2 doped with divalent and trivalent ions with ionic radii in the range of 0.5-0.95 Angstrom at 3 GHz can be very low: 6 x 10(-5) (Q approximate to 17 000) at a temperature of 300 K. The tan delta of undoped pure TiO2 disks increases when the disks are cooled from 300 K to similar to 100 K. At temperatures <100 K, the tan delta decreases rapidly, which is interpreted as carrier freeze-out. The tan delta for all the high-Q doped TiO2 polycrystalline samples smoothly decrease to similar to 5 x 10(-6) (Q approximate to 200 000) at 15 K, comparable to that of single crystals.