The synthesis and microwave dielectric properties of SrxBa1−xAl2Si2O8 and CayBa1−yAl2Si2O8 ceramics

Dense, single-phase SrxBa1−xAl2Si2O8 (0 ≤ x ≤ 1) and CayBa1−yAl2Si2O8 (0 ≤ y ≤ 0.05) ceramics were synthesized and then structurally and dielectrically characterized. The substitution of Ba with Ca or Sr promotes the transformation of hexacelsian to monocelsian. The substitution with Ca led to a more-than-two-times-lower Q × f value at y = 0.05, whereas the Q × f value of the Sr0.05Ba0.95Al2Si2O8 (x = 0.05) was only 5% lower than the Q × f value of the BaAl2Si2O8, which exhibited Q × f values of 70,600 and 77,700 GHz when sintered at 1500 °C for 12 and 40 h, respectively. The improvement in the Q × f value with the prolongation of the heat-treatment time, which can be attributed to an increase in the Al:Si ordering, was also noticed for other SrxBa1−xAl2Si2O8 solid solutions. In contrast to the dielectric losses, the permittivity (ɛ = 7.3 and 7.2 at 1 MHz and 10.5 GHz, respectively) did not change significantly with the composition and the sintering conditions.