Ruddlesden-Popper Nickelates Research Articles

Synthesis, Structure, and Properties of Ln4Ni3O10-δ (Ln = La, Pr, and Nd)

The Ruddlesden-Popper nickelates Ln4 Ni3O10-δ, with Ln = La, Pr, and Nd, have been synthesized by a precursor method. Power X-ray diffraction studies show orthorhombic symmetry with space group Fmmm for all three compounds; however, electron diffraction patterns of single crystals show that the space group symmetry is lower than F or C. The orthorhombic unit cell parameters decrease monotonically with decreasing effective ionic radius of the lanthanide ion. The distortion from ideal tetragonal symmetry and the orthorhombic strain increase with decreasing radius of the lanthanide ion; Nd was the smallest lanthanide for which Ln4 Ni3O10-δ could be stabilized. Pr4Ni3O10-δ and Nd4Ni3O10-δ are oxygen deficient (δ ∼ 0.15), while La4Ni3O10 is nearly stoichiometric. The resistivity measurements indicate metallic temperature dependence for La4Ni3O10, and a metal-to-metal transition for Pr4Ni3O10-δ and Nd4Ni3O10-δ at 145 and 165 K, respectively. These anomalies are attributed to charge-density-wave driven instabilities and are confirmed by differential scanning calorimetry to coincide with first-order structural phase transitions. The magnetic susceptibility of metallic La4Ni3O10 is nearly temperature independent above 100 K, and shows paramagnetic behavior at lower temperatures. Pr4Ni3O10-δ and Nd4Ni3O10-δ show paramagnetic behavior in the temperature range 4-300 K, due to the large magnetic contributions of the lanthanides to the total moment.