Precipitation behavior of highly Sr-doped LaPO4 in phosphoric acid solutions

Abstract

The precipitation condition of LaPO4 in phosphoric acid solution was investigated under both atmospheric and humidified conditions. The crystal morphology, Sr doping level, H2O incorporation, and high temperature stability of Sr-doped LaPO4 precipitates were also analyzed. Increasing pH2O from 0.01 to 1 atm extends the precipitation region of LaPO4 in phosphoric acid solutions toward higher temperatures by nearly 100 °C. Under such conditions (e.g. T = 250 °C and pH2O = 1 atm), it is possible to obtain aggregated crystals up to 200 μm. The Sr doping level in LaPO4 shows a strong dependence on the precipitation ratio of La, X_[La]. The Sr doping level is higher in the low X_[La] region, reaching 20 mol% at maximum. This value is one order of magnitude higher than the previously reported solubilities. It was confirmed H2O is certainly incorporated in the bulk by Sr doping. The solubility of Sr in LaPO4 would be sufficiently high (at least 20.1%) even at 600 °C; however, it becomes considerably lower at 1200 °C.