Structure Transformation between Perovskite-type and B-type Rare Earth Structures

LaLnO3 (Ln = Dy, Ho, Y, Er, and Yb) and La(Ln, Ln’)O3 (Ln, Ln’ = Dy, Ho, Er, and Yb) systems were synthesized by solid state reaction method and characterized by X-ray diffraction. When Ln = Er or Yb which has smaller ionic radius than that of Y3+ (0.900 Å), the LaLnO3 showed an orthorhombic perovskite structure, while when Ln = Dy or Ho which has larger ionic radius than that of Y3+, it showed a monoclinic B-type rare earth structure. Next, the solid solution system of LaHoxYb1-xO3 was investigated in order to clarify the crystallochemical factor affecting the structural transformation. The XRD experiments revealed that the samples with x = 0.90 (rav.=0.8977 Å) showed the orthorhombic perovskite structure, changed to the mixed phases of monoclinic B-type rare earth, and orthorhombic perovskite structures with increasing x, and then the samples with x ≥ 0.95 (rav.=0.8994 Å) showed the monoclinic B-type rare earth structures, where rav. represents the average ionic radii of Ln and Ln’.