Comment on “Microwave dielectric properties of AWO4 (A = Ca, Ba, Sr) ceramics synthesized via high energy ball milling method” by Lin Cheng, Peng Liu, Shi-Xian Qu, Huai-Wu Zhang, J. Alloys Compd. 581 (2013) 553–557

Abstract

In this letter, our comment concerns about the phase formation of CaWO4 compound in short duration by high-energy ball milling method. The article by Cheng et al. [1] reported in the J. Alloys Compd. 581 (2013) 553–557 describes that the phase pure AWO4; A = Ba, Sr, Ca compounds with scheelite structure can be produced by ball milling of the reaction mixtures at 300/450 rpm in short duration (10–30 minutes). This finding raises serious question about the pure phase formation of the AWO4 structure under the condition employed by them. We have adopted a quite similar ball milling conditions of Cheng et al. to syntheses especially the CaWO4 materials under different time durations (10 minutes −10 hours) by high-energy ball milling of the reaction mixture (CaCO3 and WO3) at 300 rpm. Based on the literature on ball milling of different oxide materials and from our present XRD results, we conclude that it is not possible to obtain the phase pure CaWO4 materials by ball-milling of the reaction mixtures at 300 rpm in short duration (10–30 minutes). Even after ball milling for 10 hours, no formation of CaWO4 phase is seen from our present XRD patterns. Subsequent annealing of the as-milled powders at high temperature may yield phase pure CaWO4 materials. Our present XRD result is absolutely different from the report of Cheng et al.