Crystal structure and Raman spectrum of hydroxyl-bastnasite-(Ce), CeCO3(OH)

Hydroxyl-bstnasite-(Ce), ideally CeCO3(OH), had been regarded isostructurall with bdstnasite-(Ce), CeCO3F, the dominant member of the bastnasite family that produces -70% of the world's supply of rare-earth elements. Using single-crystal X-ray diffraction and Raman spectroscopy, our structural analysis on hydroxyl-bastnasite-(Ce) shows that the previous assumption is incorrect. The crystal structure of hydroxyl-bastnasite-(Ce) possesses P (6) over bar symmetry with unit-cell parameters a = 12.4112(2), c = 9.8511(3) angstrom, and V= 1314.2(1) angstrom(3), in contrast to the space group P (6) over bar 2c and a approximate to 7.10, c approximate to 9.76 angstrom, and V approximate to 430 angstrom(3) for bastnasite-(Ce). Moreover, there are 6, 3, and 5 symmetrically-distinct CO3 groups, Ce cations, and (OH/F) ions, respectively, in hydroxyl-bastnasite-(Ce), but 1, 1, and 2 in bastnasite-(Ce). The two structures, nevertheless, are similarly characterized by the layers Of CO3 groups alternating with the Ce-(OH/F) layers along the c direction. The Raman spectrum of hydroxyl-bastnasite-(Ce) is dominated by three strong bands at 1080, 1087, and 1098 cm(-1) in the CO3 symmetrical stretching region, along with at least four bands in the OH stretching region. Our study further suggests that natural hydroxyl-bastnasite-(Nd) is most likely isotypic with hydroxyl-bastnasite-(Ce), rather than with bastnasite-(Ce), as previously proposed.