Effects of molten salt synthesis (MSS) parameters on the morphology of Sr3Ti2O7 and SrTiO3 seed crystals

A two-step molten salt synthesis process was utilized to fabricate Sr3Ti2O7 and SrTiO3. High aspect ratio SrTiO3 seed crystals were developed by optimizing processing conditions such as temperature, salt-to-oxide ratio, and flux type in a systematic fashion. Sr3Ti2O7 seeds were synthesized at temperatures ranging from 1050-1350 degrees C, using salt-to-oxide ratios of 3:1, 1:1, and 1:3, and various salt types, including NaCl, KCl, and a 1:1 combination of NaCl and KCl. Sr3Ti2O7 seeds synthesized at 1250 degrees C with a 1:1 salt-to-oxide ratio in 100% NaCl salt resulted in a majority of higher aspect ratio platelets and elongated platelets as opposed to lower aspect ratio cubic-like and tetragonal-like morphologies. The seeds were 10-40 mu m in length with aspect ratios of highly elongated platelets as high as 25:1. A second MSS step was used to synthesize SrTiO3 seeds of the proper composition by TiO2 addition to the Sr3Ti2O7 seeds and heat treatment at 1100 degrees C. These studies showed that highly anisotropic SrTiO3 seeds could be produced at 1250 degrees C using a 1:1 salt-to-oxide ratio in 100% NaCl flux. XRD studies of the resulting SrTiO3 seeds revealed that the increase in aspect ratio for these particular seeds also resulted in the enhancement of (200) peaks, which are of major interest for texturing of PMN-PT.