Microwave-Assisted Hydrothermal Synthesis of Ceric-Ammonium Phosphates (NH4)2Ce(PO4)2•H2O and NH4Ce2(PO4)3

The possibility of preparation of crystalline double cerium(IV) phosphates (NH4)(2)Ce(PO4)(2)center dot H2O and NH4Ce2(PO4)(3) under the conditions of microwave-assisted hydrothermal synthesis has been analyzed. It has been shown that these phosphates in a single-phase state can be obtained in the temperature range of 130-190 degrees C with a synthesis duration of >= 5 min, while the phase composition of the synthesis products is determined by the molar ratio of ammonia and phosphoric acid in the reaction mixture. Short-term (5 min) low-temperature (130 degrees C) hydrothermal synthesis under microwave heating leads to the preparation of (NH4)(2)Ce(PO4)(2)center dot H2O and NH4Ce2(PO4)(3) with a particle size of similar to 70 and similar to 200 nm, respectively. At higher temperatures and treatment times (190 degrees C and 24 h), the particle size of these phases increases to similar to 200 and similar to 500 nm, respectively. For the first time, the value of the optical band gap for (NH4)(2)Ce(PO4)(2)center dot H2O was determined to be 2.8 and 3.1 eV for indirect and direct transitions, respectively.