Dependence of microwave dielectric properties on bond valence in (Pb1-xCax)(Fe0.5Nb0.5)O3 ceramics

Dielectric properties of (Pb1-xCax)(Fe0.5Nb0.5)O-3 (0.55less than or equal toxless than or equal to0.64) have been investigated at microwave frequencies. The dielectric constant was decreased with the increase of Ca content and the Qf showed a maximum value of 9000(GHz) at x=0.62, and then decreased. The decrease of bond valence with the substitution of Ca caused the deviation of observed dielectric polarizability from the calculated one. The temperature coefficient of resonant frequency (TCF) can be adjusted from a negative value of -12.0 ppm/degreesC to a positive value of +3.4 ppm/degreesC with the increase of Ca content. This result was due to the increase of tolerance factor with Ca content. Typically, K of 77, Qf of 9000 (GHz) and TCF of -9 ppm/degreesC were obtained in the (Pb1-xCax)(Fe0.5Nb0.5)O-3.