Amorphous dysprosium carbonate: characterization, stability, and crystallization pathways

The crystallization of amorphous dysprosium carbonate (ADC) has been studied in air (21-750 degrees C) and in solution (21-250 degrees C). This poorly ordered precursor, Dy-2(CO3)(3)center dot 4H(2)O, 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 degrees 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, Dy-2(CO3)(3)center dot 2-3H(2)O; and (b) the orthorhombic kozoite-type phase DyCO3(OH) at 165 degrees C after prolonged times (15 days) or faster (12 h) at 220 degrees 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.