Sr2LaAlTiO7: a new Ruddlesden–Popper compound with excellent microwave dielectric properties

Abstract

A new n = 2 type Ruddlesden–Popper compound Sr₂LaAlTiO₇ was synthesized and characterized, and the microwave dielectric properties were investigated together with their microstructures. X-ray diffraction (XRD) Rietveld analysis and selected area electron diffraction (SAED) patterns confirmed that these compounds belong to the I4/mmm space group with tetragonal crystal symmetry. The lattice parameters were calculated as a = b = 3.840 Å and c = 20.270 Å. The interlayer polarization was considerably lower than that of the previously reported SrLa₂Al₂O₇ ceramics, and a well ordered distribution of ions along the c axis was confirmed from the high resolution transmission electron microscopy (HRTEM) images. Excellent microwave dielectric properties were obtained and an optimal combination (ε_r = 26.5, Q × f = 110 850 GHz, τ_f = 2.95 ppm °C⁻¹) was obtained for the sample sintered at 1600 °C in air for 3 h. Considering the merits of a simple preparation, less process sensitivity and, most importantly, the comparatively cheap raw materials, Sr₂LaAlTiO₇ ceramics could be expected as promising new candidate for ultra-low loss microwave dielectric ceramics.