Grain growth and electric properties of liquid phase sintered AlN ceramics with CaCN2 additives

The effect of calcium cyanamide (CaCN2) additives on the grain growth and electric properties of liquid phase sintered AlN ceramics have been investigated using an X-ray diffractometer (XRD), a scanning electron microscope (SEM), a transmission electron microscope (TEM) attached with an energy dispersive X-ray microanalyzer (EDX) and an inductance-capacitance-resistance (LCR) meter. The grain sizes of the AlN compacts containing 1.5 wt.% CaCN2 additive and sintered at 1700, 1750 and 1800 °C for 1 h are about 0.35, 0.40 and 0.56 μm, respectively. When the compacts are sintered at 1750 °C for 12 and 6 h, the grain size decreases from 1.20 to 0.87 and 1.06 to 0.80 μm with the CaCN2 additive content increased from 0.50 to 3.0 wt.%, respectively. The grain size increases from 0.29 to 0.39 μm with the CaCN2 content increased from 1.0 to 1.5 wt.% when sintered at 1750 °C for 1 h. When the AlN compact containing 1.0 wt.% CaCN2 additive is sintered at 1750 °C for 6 h, the electric resistance is 5.0×1014 Ω. For the compacts containing 0.50 wt.% CaCN2 additive and sintered at 1700, 1750 and 1800 °C for 1 h, the electric resistances are 1.6×1014, 1.4×1014 and 6.3×1013 Ω, respectively. When measured at 1–10 kHz, the relative dielectric constant decreases from 7.0 to 3.5 for the AlN compacts containing 1.0 wt.% CaCN2 additive and sintered at 1750 °C for 1 h. The relative dielectric constant decreases from 3.5 to 1.4 when the testing frequency is in the range of 10 kHz–1 MHz. The grain size of the sintered AlN compacts with 1.01 wt.% CaCN2 additive is greater than 0.6 μm and the relative dielectric constant approaches 1.0.