Evolution of the Jahn-Teller distortion of MNO{sub 6} octahedra in RMnO{sub 3} perovskites (R = Pr, Nd, Dy, Tb, Ho, Er, Y): A neutron diffraction study
Stoichiometric RMnO{sub 3} perovskites have been prepared in the widest range of R{sup 3+} ionic sizes, from PrMnO{sub 3} to ErMnO{sub 3}. Soft-chemistry procedures have been employed; inert-atmosphere annealings were required to synthesize the materials with more basic R cations (R = Pr, Nd), in order to minimize the unwanted presence of Mn{sup 4+}. On the contrary, annealings in O{sub 2} flow were necessary to stabilize the perovskite phases for the last terms of the series, HoMnO{sub 3}ErMnO{sub 3}, and YMnO{sub 3}, thus avoiding or minimizing the formation of competitive hexagonal phases with the same stoichiometry. The samples have been investigated at room temperature by high-resolution neutron powder diffraction to follow the evolution of the crystal structures along the series. The results are compared with reported data for LaMnO{sub 3}. The distortion of the orthorhombic perovskite (space group Pbnm), characterized by the tilting angle of the MnO{sub 6} octahedra, progressively increases from Pr to Er due to simple steric factors. Additionally, all of the perovskites show a distortion of the MnO{sub 6} octahedra due to the orbital ordering characteristic of the Jahn-Teller effect of Mn{sup 3+} cations. The degree of orbital ordering slightly increases from La to Tb and then remains almost unchanged for the last terms of the series. The stability of the crystal structure is also discussed in light of bond-valence arguments.
- Research Organization:
- CSIC, Madrid (ES)
- OSTI ID:
- 20023365
- Journal Information:
- Inorganic Chemistry, Journal Name: Inorganic Chemistry Journal Issue: 5 Vol. 39; ISSN 0020-1669; ISSN INOCAJ
- Country of Publication:
- United States
- Language:
- English
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