Amorphous dysprosium carbonate: characterization, stability, and crystallization pathways

The crystallization of amorphous dysprosium carbonate (ADC) has been studied in air (21–750 °C) and in solution (21–250 °C). This poorly ordered precursor, Dy2(CO3)3·4H2O, was synthesized in solution at ambient temperature. Its properties and crystallization pathways were studied by powder X-ray diffraction, Fourier transform infrared spectroscopy, scanning and transmission electron microscopy, thermogravimetric analysis, and magnetic techniques. ADC consists of highly hydrated spherical nanoparticles of 10–20 nm diameter that are exceptionally stable under dry treatment at ambient and high temperatures (<550 °C). However, ADC transforms in solution to a variety of Dy-carbonates, depending on the temperature and reaction times. The transformation sequence is (a) poorly crystalline metastable tengerite-type phase, Dy2(CO3)3·2–3H2O; and (b) the orthorhombic kozoite-type phase DyCO3(OH) at 165 °C after prolonged times (15 days) or faster (12 h) at 220 °C. Both the amorphous phase and the kozoite-type phase DyCO3(OH) are paramagnetic in the range of temperatures measured from 1.8 to 300 K.