Microwave Dielectric Properties of CaTiO3–(LiNd)TiO3–(BiNa)TiO3 Ceramics

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The microwave dielectric properties of the CaTiO3–(Li1/2Nd1/2)TiO3–(Bi1/2Na1/2)TiO3 (CT–LNT–BNT) ternary ceramics were studied on the basis of their crystal structure. The microwave dielectric constant improved from 139 to 432, and $\mathit{Qf}$ decreased continuously from 3249 to 124 GHz with an increase in BNT content in the 0.4CT–($0.6-x$)LNT–$x$BNT ternary compositions. The crystal structures of 0.4CT–($0.6-x$)LNT–$x$BNT ($x=0--0.6$) ceramics were confirmed to be perovskite with an orthorhombic crystal system $Pcmn$ (No. 62) and the lattice parameter differences between the $a$- and $c$-axes became small with increasing BNT content ($x$). The increase in the dielectric constant with the increase in BNT content could be explained by not only the large polarizability of a Bi ion but also the crystal structure change: increases in bond lengths, volumes of octahedra and cuboctaheda, and the tilt angle of an octahedron. The tendency of the crystal structure to change from paraelectric orthorhombic to ferroelectric trigonal or tetragonal perovskite structure resulted in a decrease in $\mathit{Qf}$ value with increasing BNT content.
2010-09-25