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)(ε′r) and dielectric loss (tan δ), at all the frequencies, were found to rise with progressive increase in sample's temperature albeit the rise being less at higher frequencies (≥100 kHz). The room temperature values of ε′rε′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′rε′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′rε′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.