Occupation in the Trigonal Columns of Tungstenbronze-Like Ba_6-3xSm_8+2xTi₁₈O₅₄ Solid Solutions

抄録

The microwave dielectric properties of Ba_6-3xR_8+2xTi₁₈O₅₄ (R=rare earth) tungstenbronze-like solid solutions with high dielectric constants depend on the site occupancy of large cations. The fundamental structural formula is [(R, Ba, V)₁₀]_A1[(Ba, V)₄]_A2[V₄]_CTi₁₈ O₅₄, where A1 is the rhombic site in perovskite blocks, A2 the pentagonal site, C the trigonal site, and V vacancy. The A1 and A2 sites are mainly occupied by R and Ba, respectively. The possibility that the occupation of lithium ions in C site was examined in the present study, based on lattice-parameter changes. From the present results, in the region of 0≤y≤1, for Ba₄Sm_(28-y)/3Li_yTi₁₈O₅₄ (R=Sm, x=2/3), lithium ions occupy A1 sites, as expressed in the structural formula [Sm_(28-y)/3Li_yV_2/3(1-y)]_A1[Ba₄]_A2[V₄]_CTi₁₈O₅₄; in the region of 1≤y≤7, the lithium ions also occupy C sites, as expressed in the structural formula [Sm_(28-y)/3Li_(2+y)/3]_A1 [Ba₄]_A2[Li_2/3(y-1)V_4-(2/3(y-1))]_CTi₁₈O₅₄. The microwave dielectric properties also change according to the presented structural formula.