Microwave dielectric loss of titanium oxide

The dielectric loss (tan delta) of titanium dioxide (TiO2) disks has been m easured at a frequency of 3 GHz. High-purity TiO2 sintered to almost-full d ensity exhibits a very high tan delta, which is interpreted to be due to ox ygen deficiency. To counter this, doping with stable divalent and trivalent cations, such as Mg and Al, leads to a low tan delta, probably by preventi ng Ti4+ reduction. The tan delta of polycrystalline TiO2 doped with divalen t 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 temperatur e of 300 K. The tan delta of undoped pure TiO2 disks increases when the dis ks are cooled from 300 K to similar to 100 K. At temperatures <100 K, the t an delta decreases rapidly, which is interpreted as carrier freeze-out. The tan delta for all the high-Q doped TiO2 polycrystalline samples smoothly d ecrease to similar to 5 x 10(-6) (Q approximate to 200 000) at 15 K, compar able to that of single crystals.