Understanding the phase evolution with temperature in pure (BaFe12O19) and zinc-zirconium co-doped barium hexaferrite (BaZnZrFe10O19) samples using Pawley and Rietveld analysis

Abstract

Structural changes evolution taking place in ferrites with doping and increasing processing temperature are crucial from their performance point of view. The phase evolution is generally carried out by a manual comparison of experimental X-ray diffraction (XRD) peak positions with the reference data. In this study, a combination of Pawley and Rietveld analysis has been used to analyze the M-type (MFe12O19, where M is usually Barium (Ba), Strontium (Sr) or Lead (Pb)) phase evolution in undoped as well as Zinc (Zn) –Zirconium (Zr) co-doped barium hexaferrite samples synthesized using solid state reaction route. The raw mixed a) undoped and b) Zn-Zr co-doped barium hexaferrite samples were calcined between 900 °C – 1350 °C for different time (6–12 hours) durations. The structural studies reveal that a single M-type phase formation (both in undoped and doped samples) takes place between 1200 °C – 1350 °C. Fe2O3 phase in undoped and ZrO2 and ZnFe2O4 phases in doped samples have been observed as impurities below 1200 °C. The structural data in both cases was successfully refined using P63/mmc (number 194) space group. The structural studies also reveal an expansion of the hexagonal unit cell upon Zn-Zr co-substitution. The Raman data exhibits peaks corresponding to the dominant (hexaferrite) phase in the undoped and doped samples. The scanning electron microscopy (SEM) images reveal that the grain size increases linearly with an increase in calcination temperature in both types of samples. The lower average grain size of Zn-Zr co-doped sample with respect to undoped samples (at all calcination temperatures) suggests that Zn and Zr act as grain growth inhibitors. The study provides a more software oriented means of analyzing phase evolution in ferrites in particular and materials in general.