Molten-salt-mediated synthesis and low-temperature electrical conduction of LnCoO3 (Ln = Pr, Nd, Sm, and Gd)

• Orthorhombic LnCoO3 (Ln = Pr, Nd, Sm, and Gd) has been prepared using a facile molten salt method.
• An orthorhombicity maximum is observed for NdCoO3.
• Increase of CoO6 octahedra tilting leads to the split and shift of bending mode of CoO bond.
• The bulk conductivities for LnCoO3 are determined by impedance technique.

A series of perovskite compounds LnCoO3 (Ln = Pr, Nd, Sm, and Gd) have been prepared using a facile molten salt method. This methodology is demonstrated convenient to obtain single-phases by avoiding aggregates, superior to the conventional solid state reactions. All LnCoO3 samples crystallized in an orthorhombic structure. Structural refinements showed that the orthorhombicity reduces slightly from Pr to Nd and then increases rapidly to Gd, while CoO6 octahedra tilting exhibits a monotonous increase. Further investigation of the infrared spectrum reveals that the bending vibrational bands of CoO are split and shifted toward higher wavenumbers, while the stretching vibrations are less susceptible. All samples follow a semi-conducting behavior in a low temperature region from 100 K to room temperature. The decrease of bulk conductivity and increase of activation energies for small polarons hopping conduction with the reduction of Ln3+ ionic radius were interpreted in term of the bandwidth of the eg band.