Hydrothermal Syntheses and Structural Phase Transitions of AgNbO_3

摘要

The phase-pure AgNbO_3 has been prepared through the hydro-thermal reactions of NH_4HF_2, Ag_2O, and Nb_2O_5. The room-temperature powder X-ray diffraction analysis reveals that it crystallizes in orthorhombic perovskite lattice with a space group of Pmc2_1 and cell parameters a = 15.6999(9), b = 5.5521(1), and c = 5.5830(1) A. The temperatures, pH values, and times play crucial roles in obtaining phase-pure silver niobate. The structural phase transitions were observed at 813 K from cubic to tetrahedral phase and to final ortho-rhombic phase at 718 K, confirmed by TGA-DTA.