BaLa 4 Ti 4 O 15 (BLT) is a hexagonal perovskite-related compound with a temperature coefficient of resonant frequency ( f ) of À2 ppm/ C, relative permittivity ð" r Þ $ 44 and figure of merit ðQ Á f Þ $ 44000 GHz. Ba 4 Nd 9:333 Ti 18 O 54 (BNT) has a tungsten-bronze-related structure with " r $ 78, Q Á f % 11000 GHz and f of þ47 ppm/ C. The microstructures and microwave dielectric properties of xBNT-(1 À x)BLT (0 x 1) composite ceramics have been studied. X-ray diffraction analysis and scanning electron microscopy revealed that there was limited inter-reaction between the two phases and that samples were composed largely of BNT and BLT, although some deterioration in measured " r with respect to calculated values was observed. The optimum compositions were x ¼ 0:55 and 0.75 for which " r $ 63, f $ À20 ppm/ C and Q Á f > 10;000 GHz.

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and MgO in order to tune the temperature coefficient of the resonant frequency (s f ) and improve the MW quality factor (Q Â f r ) Optimized compositions, 0.45La(Zn 0.395 Ti 0.385 Ta 0.01 Al 0.21 )O 3 -0.55CaTiO 3 (LZT-CT) and 0.32Nd (Zn 0.45 Mg 0.05 Ti 0.5 )O 3 -0.10NdAlO 3 -0.58CaTiO 3 (NZT-CT)were prepared by solid-state reaction and have been characterized. X-ray diffraction (XRD) and scanning electron microscopy revealed that both compositions were single phase with a bulk microstructure composed of equiaxed grains (B10 lm). Electron diffraction and XRD demonstrated that, at room temperature, LZT-CT and NZT-CT were orthorhombic with space group Pnma, consistent with an a À a À c 1 tilt system. Diffraction contrast transmission electron microscopy revealed a complex domain structure consisting of ferroelastic and antiphase domain boundaries. LZT-CT and NZT-CT had zero s f , e r 5 49 and 44, Q Â f r 5 29 600 GHz (at 1.957 GHz), and 32 200 GHz (at 1.971 GHz), respectively.

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