123 Phases in Ce-La-Nd-2Cu-Mg-O and Ce-2Nd-2Cu-Mg-O samples

Abstract

We show that the substitution of lanthanum by neodymium, whose oxide melts at a temperature 500°C lower than La₂O₃, appreciably facilitates the synthesis of 123 phases with their Cu(1) positions fully or selectively substituted by magnesium. 123 phases with unit cells doubled in plane ab (phases “336”) and with compositions close to Ce₂(La_1.4Nd₂Ba_0.6){ Cu ²⁺_3.4 Cu ³⁺_0.6 } [Mg₂]O₁₆ (a = b = 0.5498(5) nm, c = 1.6425(8) nm), and Ce₂(La_1.7Nd₂K_0.3){ Cu ²⁺_3.4 Cu ³⁺_0.6 } [Mg₂]O₁₆ (a = b = 0.5498(5) nm, c = 1.6488(8) nm), and Ce₂(Nd_3.4Ba_0.6){ Cu ²⁺_3.4 Cu ³⁺_0.6 } [Mg₂]O₁₆ (a = b = 0.5474(5) nm, c = 1.6425 nm), where the parentheses indicate the Ba positions, the braces indicate the Cu(2) positions, and the brackets indicate the Cu(1) positions, were synthesized using modified nitrate technology at 810°C in flowing oxygen. The existence of Cu³⁺ in the Cu(2) positions endows the phases with electrical conductivity. The conductivity versus temperature curves show the semiconductor trend. The samples do not experience superconducting transitions up to 60 K.