Effects of zinc substitution on crystal structure and microwave dielectric properties of CaLa4Ti5O17 ceramics

Zinc-substituted CaLa4Ti5O17 microwave dielectric ceramics with the composition of Ca1-xZnxLa4Ti5O17 (x=0-1) were prepared by a solid-state reaction method. The effects of zinc substitution on sintering behavior, crystal structure, and microwave dielectric properties of CaLa4Ti5O17 ceramics were investigated. Zinc substitution can effectively lower the sintering temperature of CaLa4Ti5O17 ceramics from 1500 degrees to 1100 degrees C. X-ray diffraction and Raman spectra analysis reveal that with increasing zinc content, the n value of the A(n)B(n)O(3n+2) structures changed and distinct compounds formed. With increasing Zn2+ content, the perovskite-slabs decreased from 5-[BO6] to 4.5-[BO6] in the range of 0.13 <= x <= 0.2, and then collapsed to 4-[BO6] at about x=0.6, with Zn2TiO4 as the secondary phase. The microwave dielectric properties of the sintered ceramics vary with the Zn2+ content. The present ceramics with a small amount of zinc substitution show a relatively small temperature coefficient of resonant frequency of 4.9-8.7 ppm/degrees C, epsilon(r) of 57-58, and a Q x f value of 11 300-17 400 GHz. When x=0.01, the best combination of dielectric properties, a near-zero temperature coefficient of resonant frequency of tau(f)similar to 4.9 ppm/degrees C, epsilon(r)similar to 57.6, and Q x f similar to 17 100 GHz, is obtained.