Superconductivity of the ternary ruthenium compounds HfRuP and ZrRuX (X = P, As, Si or Ge) prepared at a high pressure

Using a wedge-type cubic-anvil high-pressure apparatus, equiatomic Ru compo unds HfRuP and ZrRuX (X =P: As, Si or Ge) with layered structures have been prepared at high temperatures and high pressures. The super-conducting tra nsition temperatures T-c of these compounds were 12K for HfRuP, 13 K for Zr RuP, 11.5 K for ZrRuAs, 12.2K for ZrRuSi and 10.5 K for ZrRuGe. The electri cal resistivities of these ternary Ru compounds have been measured as funct ions of applied magnetic field at low temperatures. The upper critical fiel ds H-c2 Of HfRuP, ZrRuP, ZrRuAs, ZrRuSi and ZrRuGe are 14, 16, 14.1, 14.5 a nd 8.3 T respectively. The value of H-c2 for ZrRuP is the highest among the equiatomic Ru compounds The coherence lengths of these compounds are 48.5 A for HfRuP, 45.4 Angstrom for ZrRuP. 48.3 Angstrom for ZrRuAs, 47.7 Angstr om for ZrRuSi and 63.0 Angstrom for ZrRuGe. The superconductivity of the te rnary Ru compounds is discussed.