Stability of the Jahn-Teller effect and magnetic study of LaMnO3 under pressure -: art. no. 064426

We have studied the crystal structure of LaMnO3 under pressure up to 80 kbar at room temperature by TOF neutron diffraction. The analysis of the crystal structure as a function of pressure has revealed that the Jahn-Teller (JT) distortion is stable up to about 70 kbar. The contraction of the MnO6 octahedra is nearly isotropic, but the average tilt angle diminishes with increasing pressure. This behavior shows that LaMnO3 evolves towards a wider electronic band system. Above 70 kbar the compound undergoes a transition to an unknown phase. This transition is probably due to the suppression of,the Jahn-Teller effect because of the closing of the JT gap: the ionic Mn3+ species disappear and the system evolves towards a metalliclike phase. At low temperature the effect of the applied pressure is first to increase the transition temperature and second to suppress magnetic ordering when the metalliclike phase is reached.