R.F. and microwave dielectric properties of (Zn0.95M0.05)2TiO4 (M = Mn2+, Co2+, Ni2+ or Cu2+) ceramics

Here, we report our results on the synthesis and properties of pure and 3d transition metal substituted zinc ortho-titanate (Zn1−xMx)2TiO4 dielectrics. Polycrystalline (Zn0.95M0.05)2TiO4 (M = Mn2+, Co2+, Ni2+ or Cu2+) samples of sintered density ≥94%, were prepared by ceramic powder mixing and solid state reaction followed by sintering (in air) between 1060 and 1180 °C. The XRD patterns of the furnace cooled samples revealed single ortho-titanate tetragonal inverse spinel phase. The SEM micrographs showed fairly uniform grains between 5 and 25 μm depending upon the composition. Dielectric measurements on the samples were made at low frequencies (1 kHz to 1 MHz) from 30 to 450 °C. The dielectric constant ( ε ′ r ) and dielectric loss (tan δ), at all the frequencies, were found to rise with progressive increase in sampleʹs temperature albeit the rise being less at higher frequencies (≥100 kHz). The room temperature values of ε ′ r were between 21 and 26 (depending on the 3d M2+ ion) and remained almost constant in the entire low frequency range ≤100 kHz. Both ε ′ r and tan δ were found to decrease with increasing frequency at higher temperatures (>200 °C). At microwave frequencies (7.0–7.5 GHz), the room temperature values of ε ′ r for all the (Zn0.95M0.05)2TiO4 samples were found to be in the range 18–20 and the unloaded quality factor (Qu·f) values ranged between 2100 and 9650 GHz. The (Zn0.95M0.05)2TiO4 (M = Mn2+ or Cu2+), samples exhibited over four times improvement in quality factor vis-à-vis pure Zn2TiO4, which is attributed to relative increase in grain size and density in case of Cu2+, and reduction in tetragonality of the unit cell for Mn2+ substitution.