Refractories based on 3Er2O3-Ta2O5

Crystal structures and magnetic properties of rare earth tantalates RE3TaO7(RE = rare earths)

“…The refined lattice and positional parameters are listed in tables 1 and 2, respectively. These lattice parameters are in good agreement with those reported previously [1][2][3][4][5][6][7][8]. 2(a) shows the fluorite-type structure.…”

“…Rare earth tantalates RE 3 TaO 7 (RE = rare earths) show polymorphic modifications based on a fluorite-type lattice. The RE 3 TaO 7 compounds containing small rare earth ions (RE = Ho-Lu) have a defect-fluorite-type cubic structure in which RE and Ta ions randomly occupy the cation sites in the molar ratio of 3:1 [1][2][3][4][5][6][7][8]. The RE 3 TaO 7 compounds with RE 3+ larger than Ho 3+ crystallize in an orthorhombic weberite-type supercell with dimensions a ∼ 2a fluorite , b ∼ c ∼ √ 2a fluorite [5][6][7][8].…”

Formation and Stability Regions of the High‐Temperature Fluorite‐Related Phase in the R2O3‐Ta2O5 System (R = La, Nd, Sm, Ho, Er, and Yb)

“…Phase equilibrium diagrams of the R 2 O 3 -Ta 2 O 5 system have been reported for R ‫ס‬ La, 1 Eu, 2 Gd, 3 Tb, 4 Er, 5,6 Lu, 7 and Y. [8][9][10] According to those studies, three compounds, with R 2 O 3 :Ta 2 O 5 stoichiometries of 3:1, 1:1, and 1:3, commonly represented stable phases.…”

“…T HE R 2 O 3 -Ta 2 O 5 system (where R is a rare-earth element) has been of interest from the standpoint of the science and technology of high-temperature structural ceramics, such as refractories and coatings, and of functional ceramics, such as lasers, optoelectronics, ferroelectronics, and solid-state ionics. Phase equilibrium diagrams of the R 2 O 3 -Ta 2 O 5 system have been reported for R ‫ס‬ La, 1 Eu, 2 Gd, 3 Tb, 4 Er, 5,6 Lu, 7 and Y. [8][9][10] According to those studies, three compounds, with R 2 O 3 :Ta 2 O 5 stoichiometries of 3:1, 1:1, and 1:3, commonly represented stable phases.…”

“…The R 3 TaO 7 (R 2 O 3 :Ta 2 O 5 ‫ס‬ 3:1) phases are believed to show polymorphic modifications based on the fluorite lattice, [11][12][13][14][15] because of the ordering of the cations and anions in each sublattice. These compounds have been reported to have orthorhombic structures and to be related to weberite, in the case of large rare-earth cations (R ‫ס‬ La 1 or Gd 3 ), or to be solid solutions with a defect-fluorite cubic structure, in the case of small rare-earth cations (R ‫ס‬ Eu, 2 Tb, 4 Er, 5,6 Lu, 7 or Y [8][9][10] ). Allpress and Rossell 12 found that the R 3 TaO 7 phase was one of two we-berite-type phases, depending on R: the first, labeled W1 type, was a compound belonging to the space group Cmcm when R ‫ס‬ La; the second, labeled W2 type, was a compound belonging to the space group C222 1 when R ‫ס‬ Nd through Y.…”