Formation of Tungsten Bronze-Type (Ba _{6- 3x}Sm _{8+ 2x})_αTi _18-yAl_yO ₅₄ (α=1+y/36) Solid Solutions and Microwave Dielectric Properties

The composition range of tungsten bronze-type Ba_6-3xSm_8+2xTi₁₈O₅₄ solid solutions, which are excellent microwave dielectric resonators, has been extended to (Ba_6-3xSm_8+2x)_αTi_18-yAl_yO₅₄ (α=1+y/36) with the B-site substituted by Al. In this two-dimensional solid solution region, (Ba_4.2Sm_9.2)_αTi_18-yAl_yO₅₄ (0≤y ≤1.61), which includes the best end member composition (x=0.6) of Ba_6-3xSm_8+2xTi₁₈O₅₄ solid solutions, was selected for study of solid solutions and their dielectric properties. In the whole region of the solid solution formula, tungsten bronze-type solid solutions have been formed and the dielectric constants, Q·f values and τ _f have been measured. ε _r and τ _f decreased as the amount of substituted Al increased. The decrease in τ _f with Al substitution is expected to be especially large for dielectric materials with large positive τ _f. These properties are discussed in terms of the structure.