Low-temperature sintering and microwave dielectric properties of Al2TeO6-TeO2 ceramics

We propose Al2TeO6-TeO2 ceramics as a candidate for use as low-temperature co-fired ceramics (LTCC). We investigated microwave dielectric properties and low-temperature sintering conditions for Al2TeO6-TeO2 ceramics. The calcined Al2TeO6 powders were sintered at 900 degrees C for 2-10 h with 30-50 wt% additive TeO2. X-ray powder diffraction patterns showed that the sintered samples were Al2TeO6-TeO2 composite with no other phase. The apparent density was improved with the additive TeO2 content of up to 45 wt%. The dielectric constant (er) increased by adding TeO2 content from 35 to 45 wt%, although the quality factor (Q . f) decreased. During sintering at 900 degrees C , the epsilon(r) of the Al2TeO6-TeO2 decreased slightly, whereas the Q . f increased gradually. The observed microstructures showed that the longer sintering time makes fewer pores in Al2TeO6-TeO2 ceramics. Sintering at 900 degrees C for a long time contributes to densification, but it simultaneously causes TeO2 evaporation. To prevent TeO2 evaporation, we investigated the effects of annealing at 750 degrees C after sintering at 900 degrees C . Apparent densities or er for the annealed samples were higher than those of the non-annealed samples. The Q . f improved with increasing annealing duration time, suggesting that sintering proceeded well during annealing with slower TeO2 evaporation at 750 degrees C. The results show that annealing at 750 degrees C is effective to facilitate sintering and to control TeO2 evaporation. (C) 2015 Elsevier B.V. All rights reserved.