Low-temperature Sintering Of Titanate Zinc Dielectric Ceramics

Zinc titanates ceramics have low sintering temperature (1100℃) and promising properties, and they can be sintered at 1100℃ without sintering aids. But hexagonal zinc metatitanate (ZnTiO₃) decomposes to orthotitanate (Zn₂TiO₄) with relatively bad microwave dielectric properties at ⁹45℃. It is extremely sensitive to the kinds and adding amount of raw materials and sintering aids to zinc titanates ceramics sintering and phase transition. So, it is very meaningful to prepare zinc titanates ceramics with relatively low sintering temperature and promising dielectric properties.Zinc titanate ceramics were prepared by conventional mixed-oxide method combined with a chemical processing. Doping oxides were added as sintering aids to lower the sintering temperature of the ceramics. Effects of raw materials on the low-temperature sintering and doping additions on microstructure and dielectric properties of zinc titanate ceramics were investigated.By conventional mixed-oxide method combined with a chemical processing, zinc titanates ceramics were prepared using zinc hydroxide carbonate, zinc acetate, TiO₂ and nanometer TiO₂. It was extremely sensitive to TiO₂ to the low- temperature sintering zinc titanates ceramics, while the effects of ZnO on the low- temperature sintering were not sensitive. The sintering temperature of samples with nanometer TiO₂ as raw materials decreased for 70℃ compared to that of samples with TiO₂.Based on the investigation of the effects of raw materials on the low-temperature sintering, zinc hydroxide carbonate and nanometer TiO₂ were selected to prepare zinc titanate ceramics with V2O5 and WO3 additions. The results showed that the sintering temperature was lowed significantly by V₂O₅ and WO₃ additions. Zinc titanate ceramics with 0.75wt% V₂O₅ addition could be well sintered to approach 96.1% theoretical density at 900 ℃, and to approach 95.2% theoretical density at 930 ℃ with 3.00wt% V₂O₅ addition. Also the phase transition temperature from hexagonal ZnTiO₃ phase to cubic Zn₂TiO₄ was lowed by adding V₂O₅. It was noticed that V enriched in the boundary of the exaggerated grains, while not be detected in the inner of exaggerated grains or in the boundary of small grains. At sintering temperature <950℃, orthotitanate phase Zn₂TiO₄ in zinc titanate ceramics with ≤1.00wt% WO₃ additions became major phase, while zinc metatitanate ZnTiO₃ became major phase with ≤1.00wt% WO₃ additions. For zinc titanate ceramics with V₂O₅ additions, the dielectric constants ε_r increased with the sintering temperature increasing. The highest dielectric constant (it reached 40.8) obtained at 950℃ when the amount of V₂O₅ addition reached 0.75wt%. The Q×f values of 0.75wt% V₂O₅-doped zinc metatitanate-based ceramics reached 8873GHz at 900℃ sintering temperature, while the dielectric constant reached 21.3. For zinc titanate ceramics with 1.00wt% WO₃ additions at 900℃ sintering temperature, ε_r=23.6 and tgδ=3.03×10^-3 in 10MHz region. It could be concluded that dielectric properties were affected seriously by adding sintering aids.To obtain zinc titanate ceramics with good dielectric properties, B₂O₃ was addedon the base of V2O5 and WO3 additions. The sintering temperature of zinc titanate ceramics was lowed by multiplex oxides of V2O5-B2O3 and WO3-B2O3 added. The bulk density of zinc titanate ceramics with 1.00wt% 3V2O5-B2O3 multiplex oxides addition reached 95.7% theoretical density at 900 °C. For zinc titanate ceramics with 1.00wt% 3WO3-B2O3 multiplex oxides addition, the bulk density reached 94.1% theoretical density at 930°C. The exaggerated grain growth resulted from single oxide V2O5 addition was restrained because of B2O3 added. For zinc titanate ceramics with 1.00wt% V2O5-B2O3 additions at 930°C sintering temperature, ï¿¡r=27.3 and tg<5= 1.92x10* in 10MHz region. In addition, the phase decomposition resulted from single oxide WO3 addition was restrained because of B2O3 added, and nano-size Zn2Ti3Og phase, a low temperature form of ZnTiC>3, precipitated in Zn2TiO4 ph...