Boron substitution in ternary metal phosphide superconductors

Partial substitution of boron for phosphorus in the ternary phosphide superconductors ZrRuP and LaRu₂P₂ induces highly anisotropic structural changes and suppresses the superconducting transition temperatures. Undoped ZrRuP [hexagonal, a=6.445(4) Å, c=3.765(2) Å] systematically expands for ZrRuP_1−xB_x (x=0.05, 0.10, 0.15, 0.20, 0.40) in the a direction to 6.949(4) Å and shrinks in the c direction to 3.601(3) Å. Superconductivity is still present in the boron-substituted samples, although T_c drops from 10.1 K in ZrRuP to 5.6 K in ZrRuP_0.6B_0.4. LaRu₂P₂ [tetragonal, a=4.032(2) Å, c=10.632(7) Å] remains essentially unchanged along the a axis [a=4.037(1) Å] upon substitution at a starting composition of LaRu₂P_1.6B_0.4, but shrinks along the c axis to 10.477(5) Å. Accordingly, the superconducting T_c drops from 4.0 K for LaRu₂P₂ to 2.0 K for LaRu₂P_1.6B_0.4.