Abstract:
The Ca(B'Ta-1/2(1/2))O-3 [B' = La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Y, Er, Yb, and In] double perovskite-type ceramics have been prepared by the conventional solid-state ceramic route. The phase purity and surface morphology of the sintered ceramics have been studied by X-ray diffraction (XRD) and scanning electron microscopy methods. XRD study revealed intersubstitution between Ca and B' ions. Ca(B'1/2Ta1/2)03 ceramics have relative permittivity (epsilon(r)) in the range 23-30, normalized quality factor (Q(u) x f) 20600-59200 GHz, and temperature coefficient of resonant frequency (tau(f)) -6 to -35 ppm/degrees C. The dielectric properties of Ca(B'Ta-1/2(f/2))O-3 ceramics have been tailored by the addition of positive tau(f) materials such as CaTiO3, TiO2, Ba(Y1/2Ta1/2)O-3, and Ba(Yb1/2Ta1/2)O-3, which form a solid solution or a mixture phase with the parent compound. The 0.7Ca(Y1/2Ta1/2)O-3-0.3Ba(Y1/2Ta1/2)O-3 ceramic has epsilon(r) = 27.5, Q(u) x f = 41900 GHz, and tau(f) = -1.2 ppm/degrees C, and the 0.6Ca(Yb1/2Ta1/2)O-3-0.4Ba(Yb1/2Ta1/2)O-3 ceramic has epsilon(r) = 27.7, Q(u) x f = 48000 GHz, and tau(f) = 1.8 ppm/degrees C.
