New mercury-based superconductors with the "1201" structure Hg0.4Pr0.6Sr2-xPrxCuO4+δ and Hg0.3Pb0.7Sr2-xLaxCuO4+δ

Abstract Two families of mercury-based superconductors, Hg 0.4 Pr 0.6 Sr 2− x Pr x and Hg 0.3 Pb 0.7 Sr 2− x La x CuO 4+δ , with a T c onset of 41 K, have been isolated. The praseodymium phase exhibits a narrow existence range x ⩽ 0.1; in the lead phase, lanthanum can be substituted for strontium up to x = 0.65. The X-ray diffraction and high-resolution electron microscopy analyses show that they both belong to the “1201” series; the structures can be described from the intergrowth of single perovskite layers with double oxygen-deficient rock-salt layers built up from the mixed layers [Hg 0.4 Pr 0.6 O δ ] ∞ and [Hg 0.3 Pb 0.7 O δ ] ∞ . Evidence is found for ordering between mercury and praseodymium and a structural model is proposed.