Isostructural Cd3E2 (E = P, As) Microcrystals Prepared via a Hydrothermal Route

Cd3P2 and α' '-Cd3As2 microcrystals were hydrothermally synthesized at 180 °C in aqueous ammonia. Their powder X-ray diffraction patterns were indexed to an isostructural tetragonal lattice with a = 8.7360 Å, b = 12.2953 Å for Cd3P2 and a = 8.9843 Å, b = 12.6550 Å for Cd3As2 (α' '-, metastable phase) with good reliability (instead of the stable phase α-Cd3As2). Transmission and scanning electron microscopy (TEM, SEM) images showed that Cd3P2 crystallized as octahedral microcrystals of 100−500 nm with {101} cleavage planes, and α' '-Cd3As2 crystallized as fine nanocrystals (20 nm), which assembled into secondary spherical particles of 100 nm. X-ray photoelectron spectroscopy (XPS) showed that the as-prepared hydrothermal products were pure Cd3E2 (E = P, As) without obvious surface oxidation or hydrolysis. Cd3P2 octahedral microcrystals showed three Raman peaks at 250.7, 300.8, and 599.1 cm-1, and α' '-Cd3As2 nanocrystals showed two broad and red-shifted peaks at 189 and 244.5 cm-1, both of which were different from their bulk counterparts. Their optical absorption spectra were characterized, and α' '-Cd3As2 nanocrystals showed an obvious blue-shift of the absorption onset.