A new solution phase synthesis of cerium(IV) pyrophosphate compounds of different morphologies using cerium(III) precursor

摘要

Here we report synthesis of undoped/doped cerium(IV) pyrophosphate compounds by a new solution phase method employing cerium(III) nitrate as metal precursor and H2O2 as oxidizing agent. The phase composition and microstructure of various samples is studied and the importance of various reactants and processing conditions in obtaining cerium(IV) pyrophosphates is analyzed. The phase development in material is studied by thermogravimetric analysis/differential thermal analysis (TGA/DTA), differential scanning calorimetry (DSC), and X-ray diffraction (XRD), and the microstructures of powders and sintered specimen are analyzed by scanning electron microscopy (SEM) and high resolution-transmission electron microscopy (HR-TEM). XRD shows that crystalline CeP2O7 phase is obtained only when precipitation is performed at pH <2. SEM shows that for P/Ce = 2 M ratio the pyrophosphate powders show sheet-type morphology but for P/Ce = 2.5 M ratio morphology changes to honeycomb-type, which is due to the coalescence of individual sheets in the presence of excess phosphoric acid. The variation in electrical conductivity of sintered specimen with temperature is studied by electrochemical impedance spectroscopy (EIS) in humid atmosphere (water vapor pressure, pH(2)O = 0.12 atm) for the possible application as electrolyte in ceramic electrolyte fuel cells in 110-230 degrees C range. With increasing temperature, the conductivity of a Gd3+-doped CeP2O7(Ce0.9Gd0.1P2O2; CGP) specimen increases from 1.48 x 10(-3) S cm(-1) at 110 degrees C to 1.04 x 10(-2) S cm(-1) at 190 degrees C. Similarly, UV-visible spectroscopy is performed for application as sunscreen materials and good UV absorption behavior is observed in 200-400 nm range. (C) 2019 Elsevier B.V. All rights reserved.