The effect of nitrogen vacancies in La3Ni2B2N3−δ

2010 
Polycrystalline samples of the layered boronitride superconductor La3Ni2B2N3−δ with various nominal nitrogen stoichiometries and identified an approximate width of formation ranging from δ ~ 0.1 to δ ~ 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 δ an increase of the residual resistivity ρ0 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).
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