Abstract
We present high-temperature powder x-ray diffraction data of the orbital-order-induced structural distortion of RMnO3, with R a rare earth element. The associated phase transition takes place in a temperature interval of ≈200 K in which the orbitally ordered phase and the orbitally disordered phase coexist. We analyse the evolution of the RMnO3 perovskite structure with the size of the rare-earth ion and with temperature. We show that the rotation of the MnO6 octahedra stabilizes the cooperative Jahn–Teller distortion to higher temperature.
Highlights
The rare-earth perovskites RTO3, with R a rare-earth element and T a transition metal, have been intensively studied because of their wide variety in physical phenomena such as superconductivity, ferroelectricity and colossal magnetoresistance
This transition is associated with drastic changes in the resistivity, thermo-electric power, and thermal conductivity [3]. This behaviour is associated with two consecutive transitions with decreasing temperature from an orbitally disordered, via a shortrange ordered regime, T ∗ < T < TJT, to a long-range orbitally ordered state [3]. These authors suggest that the phase transition changes from first order for LaMnO3 to second order for smaller rare earth ions, i.e. NdMnO3 and PrMnO3 [3]
Combining our work with earlier studies, we find that a smaller rare-earth ionic radius stabilizes the cooperative JT distortion to higher temperature in RMnO3 perovskites
Summary
The rare-earth perovskites RTO3, with R a rare-earth element and T a transition metal, have been intensively studied because of their wide variety in physical phenomena such as superconductivity, ferroelectricity and colossal magnetoresistance In all these phenomena, the electronic properties are intimately related to the lattice. The orbital ordering induces changes in the crystal structure and has pronounced effects on the electronic properties This transition is associated with drastic changes in the resistivity, thermo-electric power, and thermal conductivity [3]. This behaviour is associated with two consecutive transitions with decreasing temperature from an orbitally disordered, via a shortrange ordered regime, T ∗ < T < TJT , to a long-range orbitally ordered state [3]. The nature of the phase transition and the effect of ionic size of the rare earth ion remain subjects to debate
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