Table Lattice parameter ratios a c and b

In the second mechanism that applies for small RE ions, the transition could result from a subtle balance between tilt (appearance of the mode at 300 cm−1) and octahedral rigidity associated with the Goldchmidt tolerance factor and the masse effect [18]. However, the calculated value of Gd–O distance at room temperature is smaller than that of Bi–O (2.33 and 2.43 Å, respectively, according to the Shanon table) [17] which might result in higher rigidity of the octahedra.