High-Temperature Structural Disorder in R₃NbO₇

Structure and dielectric properties of Ln3NbO7 (Ln=Nd, Gd, Dy, Er, Yb and Y)

“…The XRD profiles for these four compounds are all consistent with a cubic fluorite structure and show no reflections associated with the pyrochlore structure. However, according to Raman spectroscopy analysis by Kovyazina et al 9 , Y 3 NbO 7 shows the six characteristic active Raman spectroscopy lines (A 1g ,E g ,4F 2g ) for the pyrochlore structure. It is quite possible then that the same local ordering is occurring in other Ln 3 NbO 7 (Ln = Dy, Er and Yb) compounds.…”

“…Further proof for this crystallographic assignment has been obtained in the past by Raman spectroscopy, also pointing to Gd 3 NbO 7 as a weberite related structure. 9 The peaks with relative intensities larger than 1% are indexed and others are indicated by diamond symbols in Fig. 3.…”

“…5 From Raman spectroscopy studies, Kovyazina et al 9 proposed Y 3 NbO 7 as a "domain pyrochlore" structure, in which the oxygen vacancies are ordered in the same way as in a pyrochlore structure but only at a local (domain) level. This local order was also proposed as an explanation of the non-ideal pyrochlore X-ray diffraction (XRD) profile observed.…”

“…This local order was also proposed as an explanation of the non-ideal pyrochlore X-ray diffraction (XRD) profile observed. 9 Finally, an orthorhombic weberitetype structure with space group Cmcm has been reported for Ln 3 NbO 7 (Ln = La 3+ , Pr 3+ and Nd 3+ ). [3][4][5][6][7][8]10 Some insight on this discrepancy regarding the crystal structure reported for these compounds can be obtained by contrasting the different crystal structures proposed.…”

Phase formation and dielectric properties of Ln2(Ln′0.5Nb0.5)2O7 (Ln=rare earth element)

“…These two structures can be described as a network of corner-shared BO 6 octahedra. However, a significant difference between the two is that all of the oxygen ions in weberites participate in the formation of BO 6 octahedra, but only 6 out of 7 oxygen ions participate in pyrochlore structures (see Fig. 1).…”