Effect of nitrogen to niobium atomic ratio on superconducting transition temperature of δ-NbN x powders
Tóm tắt
Powders of cubic niobium nitride δ-NbN
x
with a particle size of below 20 μm were prepared by reactive diffusion at T = 1455−1475°C under nitrogen pressures of P
1(N2) = 0.1−3 MPa and P
2(N2) = 25 MPa. For these powders, the values of the stoichiometric coefficient x, lattice parameter a, and the superconducting transition temperature Tc were measured and the a(x), T
c(x) and T
c(a) functions were analyzed. The T
c values were found to linearly grow with increasing a (decreasing structure imperfection). A maximum value of T
c (15.8 K) corresponded to a maximum value of a (4.3934 Å). Maximain the a(x) and T
c(x) curves were found to correspond to a slightly substoichiometric nitride with x = 0.98. Having synthesized cubic niobium nitrides with 0.892 < x < 1.062, we managed to measure the dependences of a and T
c on x all over the almost entire homogeneity range for δ-NbN
x
. Our a(x) and T
c(a) functions were found to reasonably agree with those previously reported for SHS-produced δ-NbN
x
powders.
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