Polymorphism of ScBO3 at the Solid Phase Synthesis from Amorphous Precursors

Abstract

Detailed X-ray studies of changes in the structure of the scandium orthoborate ScBO₃ in the process of serial isothermal annealing of the initial charge in the form of amorphous precursor were carried out. It was shown that upon successive annealing of the amorphous precursor, the crystalline phase first forms at an annealing temperature of 710°C, the positions of the reflections of which do not coincide with the positions that of the known calcite structure. This phase exists in a very narrow temperature range (≈30°C) and, when the annealing temperature is increased to 750°C, it completely transfers to the known rhombohedral phase of calcite. Using the ENDEAVOR software, the cell parameters, atom positions in the cell, and the spatial symmetry group of the new phase were determined. It turned out that the new phase corresponds to the hexagonal structure of the faterite (S.G. P63/mmc), known for other orthoborates of rare-earth elements (REE).