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

• This is the first study of dielectric properties of Al2TeO6–TeO2 sintered at 900 °C.
• The sintering at 900 °C contributed to densification, but it causes TeO2 evaporation.
• The annealing at 750 °C was effective for the further densification.
• The both εr and Q · f in the Al2TeO6–TeO2were improved with the annealing.

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 °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 (εr) increased by adding TeO2 content from 35 to 45 wt%, although the quality factor (Q · f) decreased. During sintering at 900 °C, the εr 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 °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 °C after sintering at 900 °C. Apparent densities or εr 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 °C. The results show that annealing at 750 °C is effective to facilitate sintering and to control TeO2 evaporation.