Study of quadrupole interactions in nano-LaFeO3 perovskites by time differential perturbed angular correlation

The quadrupole interactions have been investigated in the nano-and crystalline LaFeO3 perovskites by TDPAC. The TDPAC probe nuclei 140La-140Ce were produced through the nuclear reaction 139La(n, γ)140La at the heavy water experimental reactor in CIAE. One electric quadrupole interaction was detected for each material, which is assigned to the La site. The quadrupole interaction frequencies of 687.4 Mrad/s, 698.3 Mrad/s and 742.9 Mrad/s with a distribution coefficient of 0.014, 0.009 and 0.001 were observed at room temperature for the 20 nm and 40 nm nano-LaFeO3 and crystalline LaFeO3, respectively. The fitting yielded the EFG asymmetry parameter η=0, which indicates that the principal axes of the EFG are aligned with the crystallographic axes. The experimental results show that the structure of crystalline LaFeO3 is rhombohedral, the structure change towards the orthorhombic takes place from crystalline LaFeO3 to nano- LaFeO3, and the smaller the nano-grain size, the larger the change. Since frequency distribution is caused by the perturbance of neighboring atoms, the distribution coefficient increases with the decrease of the nano-grain size. (authors)