Rietveld Refinement and Dielectric Properties of CaLa4Ti5O17 and SrLa4Ti5O17 Ceramics

Katarina Demšar,a Srečo D. Škapin,b Anton Medena and Danilo Suvorovb

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

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 AnBnO3n+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 τf = –29 ppm/K for Ca- La4Ti5O17 and positive value of τf = 58 ppm/K for the Sr-analog.

Keywords: Powder diffraction, Rietveld refinement, Microwave ceramics