Rietveld Refinement and Dielectric Properties of CaLa₄Ti₅O₁₇ and SrLa₄Ti₅O₁₇ Ceramics

Katarina Demšar,^a Srečo D. Škapin,^b Anton Meden^a and Danilo Suvorov^b

^a Faculty of Chemistry and Chemical Technology, University of Ljubljana, Slovenia
^b Jožef Stefan Institute, Ljubljana Slovenia
* Corresponding author: E-mail: katarina.demsar@fkkt.uni-lj.si

Abstract
The ceramic materials of CaLa₄Ti₅O₁₇ and SrLa₄Ti₅O₁₇ were synthesized using the solid-state reaction method. Rietveld refinements of XRD data were carried out using different models obtained from the structural database and the orthorhombic structure (Pmnn space group) proved to be most suitable for both compounds. Like in similar compounds of the general formula A_nB_nO_3n+2, where perovskite-like slabs are separated by oxygen-rich layers, Ca or La and Sr or La occupy the A site. The refined occupancies indicate that Ca preferably occupies the A sites within the perovskite slabs, while Sr is preferably found within the oxygen-rich layers. The characterization of microwave dielectric properties revealed that ceramics based on these compounds exhibit permittivity in the range of 39–51, high quality factor (Qxf) in the range of 13140–14200 and negative value of temperature coefficient of resonant frequency τ_f = –29 ppm/K for Ca- La₄Ti₅O₁₇ and positive value of τ_f = 58 ppm/K for the Sr-analog.

Keywords: Powder diffraction, Rietveld refinement, Microwave ceramics