Microwave Dielectric Properties of Al-Substituted Forsterite Ceramics

In this paper, the nominal formula Mg
₂
(Si
_x
Al
_1-x
)O
_4-δ
(x≤0.2) ceramics were synthesized by traditional solid phase reaction methods, and the phase evolution and microstructures of that were investigated by XRD and SEM. The testing results of XRD and SEM show that by substitution of Al for Si in the B site of Mg
₂
SiO
₄
, the MgSiO
₃
secondary phase can be suppressed, whereas the secondary phase of MgAl
₂
O
₄
appears gradually with increasing Al-substitution amounts. The relative dielectric constants of Mg
₂
(Si
_x
Al
_1-x
)O
_4-δ
(x≤0.2) ceramics increase from 7.0 of Mg
₂
SiO
₄
to 9.5 of Mg
₂
(Si
_0.8
Al
_0.2
)O
₄
, and the Q×f value is improved significantly and reached the maximum at x=0.1 where the optimum combination of microwave dielectric properties are obtained: ε
_r
= 8.6, Q×f = 83,000 GHz, τ
_f
= -60ppm/°C.