Zn site substituting effects on structural evolution and microwave dielectric properties of rutile Zn_0.15Nb_0.3Ti_0.55O₂ ceramics

In this work, the structure–property relationship of four types of divalent ions doped rutile Zn_0.15Nb_0.3Ti_0.55O₂ microwave dielectric ceramics, including Co²⁺, (Cu_0.5Co_0.5)²⁺, (Cu_0.5Ba_0.5)²⁺, and Ca²⁺, were studied. It is found that impurity phases with contents less than 1.5% were identified in Ca²⁺ and (Cu_0.5Ba_0.5)²⁺ doped systems. There are decreased trends of axis length and cell volume along with the decrease of radius of doped ions. The extrinsic factors, including amounts of grain boundaries, and uniformity of grain size distribution, contribute to the development of microwave dielectric properties. More importantly, based on the P–V–L bond theory, it is shown that the variations of bond ionicity, lattice energy, and bond energy are responsible for the dielectric constant, quality factor, and temperature coefficient of resonance frequency, where Nb–O bonds own the largest bond ionicity and bond energy among all the types of bonds, and Ti–O bonds provide about 52% of the total lattice energy. This study provides an idea for further improving the microwave dielectric properties of rutile Zn_0.15Nb_0.3Ti_0.55O₂ ceramics by moderating the bond characteristics.