Phase changes and lattice distortion in fluorite-related phases of R3TaO7 (3R2O3·Ta2O5, R=rare earth)

Yoshiyuki Yokogawa, Masahiro Yoshimura, Shigeyuki Somiya

研究成果: Article同行評審

28 引文 斯高帕斯(Scopus)


The crystal structuresof the compounds R3TaO7 (3R2O3·Ta2O5, RLaYb, Y) were studied by X-ray diffraction method. According to the powder X-ray patterns, R3TaO7 prepared by solid state reaction at 1700°C for for 4 h showed several polymorphic modifications based on fluorite-related structures. The diffraction patterns are of cubic fluorite-like type for smaller R3+ ions. For larger R3+ ions the superlattice lines appeared and the diffraction peak of the fundamental lines was broadened and/or apparently split, which is of weberite orthorhombic type. The orthorhombic structure has monoclinic distortion of the fluorite unit cell. With the increase of the ionic radii of R3+ ions until Nd3+, the distortion of the fluorite unit cell increased. The compounds of R3TaO7 with much larger radii for RLa3+ and Pr3+, however, have a different distortion type in their unit cells. Therefore, two orthorhombic fluorite related superstructures are formed, of space group Cmcm for RLa and Pr, and C2221 for Nd, Sm, Eu, Gd, Tb and Dy. The smaller ions such as Ho, Er, Yb and Y take the cubic fluorite structure.

頁(從 - 到)1449-1456
期刊Materials Research Bulletin
出版狀態Published - 1987 11月

All Science Journal Classification (ASJC) codes

  • 材料科學(全部)
  • 凝聚態物理學
  • 材料力學
  • 機械工業


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