Electrocrystallization of PrO_2 and TbO_(2-x) from alkali hydroxide melts and characterization of the fluorite- related TbO_(2-x)

摘要

Single crystals of PrO_2 and of the oxygendeficient fluorite related phase TtbO_(2-x) have been obtainedby anodic electrocrystallization from alkaline hydroxide meltscontaining PrCl_3 and TbCl_3, respectively. Magneticmeasurements, X-ray diffraction data and TEM investigationsconfirm the identity of the products. PrO_2 crystallizes in afluorite type of structure with a=5.3945(3)? and showsparamagnetic behaviour with a magnetic moment as expectedfor Pr~(4+) (#mu#_(eff)=2.49#mu#_B, #THETA#=-109K,T_N=10K). According to precession photographs and anexamination with an area sensitive X-ray detector, TbO_(2-x)exhibits a superstructure of fluorite with a pseudocubic subcellwith a_f=5.2810(1)?. This lattice constant is intermediatebetween those of TbO_2 and Tb_2O_3 (C-type), the same istrue for its paramagnetic behaviour (#mu#_(eff)=8.58#mu#_B,#THETA#=-22K, T_N=5K). The supercell was found to behexagonal with a=25.836(1)? and c=36.672(2)?, the symmetryof the intensity distribution being monoclinic. Electrondiffraction revealed a cubic cell with a=10.6?, space group#IOTA#A-3, indicating reduction of the material in the electron beam.