STRUCTURE AND DEVITRIFICATION CHEMISTRY OF RE(PO<SUB>3</SUB>)<SUB>3</SUB> (RE=La, Pr, Nd, Gd, Dy, Y) METAPHOSPHATE GLASSES

Abstract

The devitrification and structure of RE(PO3)3 (RE = La, Pr, Nd, Gd, Dy,Y) glasses are studied by infrared spectroscopy, X-ay diffraction and differential thermal analysis. The results from devitrification experiments show that RE(PO3)3 glasses (regardless of the size of RE3+) crystallize first to give monoclinic Yb(PO3)3 type crystals. The IR spectra of devitrified. La, Pr, and Nd samples differ, however, from those of Gd, Dy and Y in the range of symmetric POP stretching frequencies. To unravel the differences demonstrated in the IR spectra of devitrified RE(PO3)3 we performed preliminary Rietveld refinement on the crystal structure of the "metastable" Nd(PO3)3 [monoclinic, P21/c a = 11.468 (4)

Structure of rare-earth phosphate glasses by X-ray and neutron diffraction

“…The more narrow features of the S(Q) data of the crystal are due to its long-range correlations. Similar relations of glass and crystals were concluded from IR spectra [23]. Thus, the structures of R metaphosphate glasses are related to the m-RP 3 O 9 structures.…”

“…Several samples have already been used in earlier investigations where the preparations are described: metaphosphate glasses with R = La [9], and with R = Pr, Nd, Dy, Y [23]. For more details see Table 1.…”

“…So the short-range order of the related glasses is expected to be closer to structures with RO 6 octahedra. On the other hand, the decrease of R-O distances, e.g., by $0.020 nm when R varies from Ce to Er [14], should have effects on details of the glass structure as it also affects the stability of the crystal structures [23]. It has to be emphasized that R-O coordination numbers of eight are also suitable for all R ranging from La to Lu (Y included) [20].…”

“…Monoclinic RP 3 O 9 crystalline structures with RO 6 octahedra form with the smaller R 3+ ions; e.g., ErP 3 O 9 [21], YbP 3 O 9 [22]. Recrystallization of metaphosphate glasses, however, leads always to isostructural monoclinic forms with N RO = 6, which are found metastable for R = La, Pr, Nd [23]. So the short-range order of the related glasses is expected to be closer to structures with RO 6 octahedra.…”

Structure of ultraphosphate glasses with small rare-earth ions by X-ray diffraction

“…Eightfold coordination exists only for the larger R 3+ ions (R = La ... Gd) in the orthorhombic (o-)RP 3 O 9 . The monoclinic (m-)RP 3 O 9 polymorph has RO 6 units and is found for all R 3+ ions, although it is metastable for the larger lanthanides, R =La, Pr, and Nd [2].…”