Microwave dielectric properties of A1−3x/2Lax(Mg1/2W1/2)O3 (A = Ba, Sr, Ca; 0.0 ≤ x ≤ 0.05) double perovskites

The structure, sintering behavior and microwave dielectric properties of A1−3x/2Lax(Mg1/2W1/2)O3 (A = Ba, Sr, Ca; 0.0 ≤ x ≤ 0.05) ceramics have been investigated in this paper by XRD, Raman, SEM and network analyzer. XRD phase analysis shows that La-substituted samples maintain the same crystal symmetry as their corresponding un-substituted samples. BaWO4, SrWO4 and CaWO4 existed as impurity phase in BLMW, SLMW and CLMW series, respectively. Small amount of La substitution increases, whereas further increase of the substitution amount decreases the B-site ordering of tungsten-based double perovskite compounds. For a well densified sample, all compounds have dielectric constant in the range 19-20. The Q × f value varies greatly with bulk density, B-site ordering and second phase. The absolute value of τf decreases as the sequence of BLMW, SLMW and CLMW series. Excellent combination microwave dielectric properties were obtained for BLMW sample with x = 0.04 sintered at 1450 °C/2 h: ɛr ∼ 20, Q × f = 87,680 GHz and τf = −1.2 ppm/°C.