High-Q pure forsterite (Mg 2 SiO 4 ) ceramics with Qf = 240,000 GHz were developed by the usual solid sintering process, using raw materials of highly purified MgO and SiO 2 .The τ f (temperature coefficient of the resonant frequency) was a large and negative: -60 to -70 ppm/ºC. To adjust the τ f value to zero, rutile (TiO 2 ) with high τ f (450 ppm/ºC) was added. When sintering temperature was selected as low as possible, TiO 2 remained in the forsterite specimen, which raised τf from a negative to positive values. For instance, the 30 wt% TiO 2 added forsterite ceramics sintered at 1200ºC yield a high density (3.3 g/cm 3 ), which same as that of the same forsterite ceramics sintered at 1350ºC. A part of added TiO 2 works for sintering aid and residual ones do for arising the τf value from negative to positive. Improved forsterite ceramics have τ f = 0 ppm/˚C, ε r = 11 and Qf = 82,000 GHz, when they contains 24 wt% of TiO 2 and sintered at 1200ºC for 2h.

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