Structural and electrical properties of lanthanum copper oxide epitaxial thin films with different domain morphologies

Herein, we investigated the domain morphologies of defect-perovskite LaCuOx (2.5 ≤ x ≤ 3.0) thin films grown on cubic SrTiO3 (100) and orthorhombic NdGaO3 (110) substrates by pulsed-laser deposition.

Role of Sr Addition on the Structure Stability and Electrical Conductivity of Sr-Doped Lanthanum Copper Oxide Perovskites

The structural and electrical properties of lanthanum copper oxide were examined as a function of Sr addition. It was observed that the lanthanum oxide and copper oxide formed La2CuO4 with K2NiF4 structure when the powder mixture was heated at 800 °C in ambient pressure. Interestingly, the samples of Sr-doped (15∼25%) lanthanum copper oxides showed single perovskite-based phase after being heated at 800 °C. Without Sr addition, a single-perovskite phase of lanthanum copper oxide was observed only under the oxygen pressure as high as 65 kbar. The stabilization of perovskite structure in lanthanum copper oxide was effectively achieved by the addition of Sr. Based on the titration analysis and pertinent defect reactions, the enhancement of perovskite stability was due to the presence of trivalent copper ions that were created to balance the electrical charge of doping ion (SrLa′). With the increasing concentration of trivalent copper ions (or electron holes equivalently) in Sr-doped samples, lanthanum copper oxide also changed from a semiconductor to metallic conductor. When the Sr dopant exceeded its solubility limit of approximately 25% in the A-site sublattice, the Sr-rich second phases, La2SrCu2O6 and Cu2SrO3, appeared and suppressed the electronic conduction drastically.

Optically Active Vibrations of Doped Lanthanum Copper Oxide Compound (La2−xMxCuO4)

Normal coordinate analysis of the optically active vibrations of doped lanthanum copper oxide (La2– x M xCuO4) has been made, with the assumption of an infinite [(CuO2)O2]6– layer model. On the basis of the results of this treatment, some of the observed bands so far reported have been successfully assigned to the Cu-O lattice vibrations. The force constants concerning Cu-O bonds have been obtained within the framework of a modified valence force field. It has been found that the present analysis based on the infinite layer model is useful for assigning the relatively high vibrational frequencies observed at the center (wave vector k = 0) of the first Brillouin zone in La2– x M xCuO4.

Anisotropic Thermal Conductivity of Superconducting Lanthanum Cuprate

The thermal conductivities of superconducting, Sr-doped lanthanum copper oxide single crystals have been measured from room temperature to below 100 mK parallel and perpendicular to the copper oxide planes. While the results indicate that the heat conduction is strongly anisotropic, the data have been analyzed in terms of a modified Bardeen-Rickhayzen-Tewordt theory of lattice thermal conductivity. It is shown that while electron scattering plays an important role in limiting the in-plane heat conductivity, this scattering channel is masked by other mechanisms for heat transport across the planes.