The crystal structure of the low-temperature A-type modification of Pr2O3 from X-ray powder and electron single crystal diffraction

Abstract The crystal structure of A-Pr2O3 has been studied by X-ray powder diffraction and high-energy electron diffraction (HEED) from single crystals. The space group has been unambiguously established as P 3 m1 (No. 164) by HEED, though the intensities of hhl reflections with l=2n+1 are very weak. These reflections are difficult to observe in X-ray diffractometry and could mislead one to consider the existence of a c-glide plane and, therefore, to a wrong space group. The structure is in agreement with the usually accepted so-called Pauling model for the A-type of rare-earth sesquioxides. The final value of Rconv=2.1% indicates an excellent refinement. Slightly distorted OPr4 tetrahedra are the most important polyhedra in this structure. They share edges and form (PrO)22+ layers, which are embedded in O2− layers. The OPr4 tetrahedron has four OPr distances of 2.344 A on average. Three of them are very short with distances of 2.305 A. These partially covalent bonds should be emphasized with respect to similar short distances in ordered PrOF structures.

[1]  P. Aldebert,et al.  Etude par diffraction neutronique des structures de haute temperature de La2O3 et Nd2O3 , 1979 .

[2]  O. Greis.  A contribution to the structural chemistry of A-type rare earth sesquioxides , 1980 .

[3]  T. Petzel,et al.  Thermodynamics of the rhombohedral-cubic phase transition of ROF with R Y, La, Pr, Nd, SmEr , 1993 .

[4]  G. Will,et al.  Powls-80 : program for calculation and refinement of Powder diffraction data , 1983 .

[5]  P. Caro.  OM4 Tetrahedra linkages and the cationic group (M0)nn+ in rare earth oxides and oxysalts , 1968 .

[6]  H. Bärnighausen,et al.  The crystal structure of A-Ce2O3☆ , 1985 .

[7]  H. Müller-Buschbaum,et al.  Zur Struktur der A‐Form der Sesquioxide der Seltenen Erden. Strukturuntersuchungen an La2O3 , 1965 .

[8]  W. C. Koehler,et al.  Neutron-diffraction study of the structure of the A-form of the rare earth sesquioxides , 1953 .

[9]  J. Boucherle,et al.  Refinement of the Nd2O3 structure and determination of the neutron scattering length of neodymium , 1975 .

[10]  R. Hoppe,et al.  Eine Notiz zum A-Typ der Lanthanoidoxide: Über Pr2O3 , 1985 .

[11]  C. Djerassi,et al.  The Crystal Structure of ScOF. , 1966 .

[12]  G. Villeneuve,et al.  Etude cristallographique et par resonance magnetique nucleaire de l'oxyfluorure ScOF , 1979 .

[13]  W. Prandtl,et al.  Über die schwarzen Oxyde des Praseodyms , 1925 .

[14]  A. Mann,et al.  The crystal structure of stoichiometric yttrium oxyfluoride, YOF , 1970 .