Structural evolution of SrLaAl1−x(Zn0.5Ti0.5)xO4 ceramics and effects on their microwave dielectric properties

Abstract

The structure and microwave dielectric properties of SrLaAl_1−x(Zn_0.5Ti_0.5)_xO₄ ceramics were determined in the composition range of x = 0–0.9. The single phase solid solutions with the I4/mmm (No. 139) space group were revealed by the Rietveld analysis of the X-ray diffraction (XRD) patterns. Abnormal variations of Sr/La–O2b and Al/(Zn,Ti)–O2 bonds along the c-axis were observed when x > 0.5, which were further confirmed by the evolutions of corresponding modes in Raman spectra. The Q × f value could be improved at the compositions around x = 0.5 and then turned to decrease rapidly with further increasing x, while the dielectric constant ε_r and the temperature coefficient of resonant frequency τ_f ascended linearly with increasing x. The drop of the Q × f value could be ascribed to the more unstable structure owing to the abnormal variations of the axial bonds, where lattice distortions and inhomogeneous regions were also confirmed by the HRTEM observation. Moreover, the infrared reflectivity (IR) spectra were recorded and fitted to further analyze the variation of the theoretical dielectric loss. The best combination of microwave dielectric properties was achieved at x = 0.5: ε_r = 23.5, Q × f = 102 000 GHz, τ_f = −3.4 ppm per °C.