A neutron and X-ray diffraction study of the structure of Nd phosphate glasses

Diffraction experiments were performed on two (Nd₂O₃)_x(P₂O₅) _1-x glasses for studying the environmental order of the Nd³⁺ cations. In case of the metaphosphate glass (x = 0.25) a combination of X-ray and neutron diffraction data was used to separate the Nd-O and O-O first neighbor peaks. An Nd-O coordination number of 6.6±0.3 and a mean Nd-O distance of (0.239±0.001) nm were determined. In the ultraphosphate glass studied (x = 0.20) these values increase to 6.9±0.3 and (0.240±0.001) nm where the Nd-O coordination number is equal to the number of terminal oxygen atoms (O_T) which are available for coordination of each Nd³⁺ cation. This indicates the formation of NdO_n polyhedra not sharing any O atom where also all O_T's are in Nd-O_T-P positions. In the metaphosphate glass the NdO_n polyhedra have to share some O_T sites.