Microwave dielectric properties of (PbCa)(FeNb)O 3 ceramics with A site Nd 3+ substitution

The influence of Nd³⁺ A site charge unbalanced substitution on the microwave properties and crystal structure of (Pb_0.48Ca_0.52)(Fe_0.5Nb_0.5 )O₃ ceramics has been investigated. For Nd³⁺ content x ≤ 2 mol-%, specimens can be produced with a single phase of perovskite structure. Other specimens with Nd³⁺ content x > 2 mol-% possessed PbO–Nb₂O₅ pyrochlore phase, with linearly increasing content with increasing x. Permittivity first increased and then gradually decreased as Nd³⁺ content increased to 20 mol-%. The unloaded quality factor Qf reached a maximum of 5210 GHz when Nd³⁺ content reached 5 mol-%. At higher Nd³⁺ content, the relative content of pyrochlore phase began to exceed 14.5%, and Qf degenerated. The temperature coefficient of resonant frequencies could be effectively controlled from 37.8 to 0.9 ppm K^-1. A small value of 7.8 ppm K^-1 was obtained in the [(Pb_0.48Ca_0.52)_1-x Nd_x](Fe_0.5Nb_0.5)O₃ system when x = 0.05 and the permittivity and Qf value were 87.9 and 5210 GHz respectively. The relationship between microwave dielectric properties and crystal structure is also discussed.