Structure and microwave dielectric properties of La5−x Sr x Ti4+x Ga1−x O17 ceramics

Single phase polycrystalline ceramics in the La5−x Sr x Ti4+x Ga1−x O17 (x = 0–1) system with A5B5O17 type layered perovskite structure were prepared via a mixed-oxide, solid state sintering route. X-ray diffraction revealed orthorhombic, Pnnm symmetry with Raman spectra consistent with this space group. The sintered ceramics exhibited a plate-like grain structure with a relative density, 94–97.5 %. The end member, La5Ti4GaO17 had e r = 42.31, Q × f o = 17,093 GHz, τ f = −34.53 but τ f could be tuned close to zero by Sr and Ti substitution at the A- and B-sites, respectively. An optimum composition La4.5Sr0.5Ti4.5Ga0.5O17 was achieved at x = 0.5 with e r = 51, Q × f o = 15,290 GHz and τ f = −2.2 ppm/oC.