The effect of nitrogen vacancies in La3Ni2B2N3

Polycrystalline samples of the layered boronitride superconductor La3Ni2B2N3?? with various nominal nitrogen stoichiometries and identified an approximate width of formation ranging from ? ~ 0.1 to ? ~ 0.4 were prepared. The relation between nitrogen stoichiometry and superconducting properties were studied by resistivity and specific heat measurements. With increasing nitrogen off-stoichiometry ? an increase of the residual resistivity ?0 and a simultaneous decrease of the superconducting transition temperature Tc from 14.2 K to 12.2 K is observed. The trend of Tc(p0) extrapolates to a clean limit Tc ~ 16K for terminal La3Ni2B2N3. The pressure dependence of Tc yields an initial slope dTc/dp = ?80mK/kbar for La3Ni2B2N2.92(5).