LANTHANIDES

Borides

• A variety of binary borides exist e.g. YB₂, YB₄, YB₆, YB₁₂, YB₆₆
• Most important are LnB₆
  • contain B₆ octahedral clusters
  • isomorphous with CaB₆
  • black, metallic conductivity

    (c.f. CaB₆ white, insulator)

  • formulated as Ln³⁺(B₆^2-)(e^-)

    except EuB₆, YbB₆ which are Ln²⁺(B₆^2-)

• MT₄B₄ compounds
  • M = Sc, Y, Ln, Th, U
  • T = Ru, Os, Co, Rh, Ir
  • of current interest for their superconductivity

    e.g. CeCo₄B₄ structure

    

    YRh₄B₄ T_c = 11.3 K

    ErRh₄B₄ T_c = 8.7 K

    also ferromagnetic (T_Curie = 0.93 K)