We have utilized the technique of neutron-induced disorder to study the effect of atomic ordering on the superconducting transition temperature ${T}_{c}$ of the $A\ensuremath{-}15$ compound ${\mathrm{Nb}}_{3}$Al. Large depressions in ${T}_{c}$ are observed when ${\mathrm{Nb}}_{3}$Al is irradiated with high-energy neutrons ($Eg1$ MeV) at 140 \ifmmode^\circ\else\textdegree\fi{}C. For samples whose value of ${T}_{c}$ before irradiation was 18.7 K no superconductivity was oberved to 1.4 K after irradiation to a fluence of $1.4\ifmmode\times\else\texttimes\fi{}{10}^{19} \frac{n}{{\mathrm{cm}}^{2}}$. The widths of the transition temperatures remain constant as ${T}_{c}$ is depressed and ${T}_{c}$ is recovered by annealing at 750 \ifmmode^\circ\else\textdegree\fi{}C after irradiation. The Bragg-Williams long-range-order parameter $S$ was determined by least-squares analysis of neutron-diffraction data from powdered samples both before and after irradiation. A reduction in $S$ of 18% is observed for samples irradiated to a fluence of $1.2\ifmmode\times\else\texttimes\fi{}{10}^{19} \frac{n}{{\mathrm{cm}}^{2}}$. For the same fluence ${T}_{c}$ is depressed to 52% of its value before irradiation. The lattice parameter ${a}_{0}$ of the $A\ensuremath{-}15$ phase expands upon irradiation, increasing from 5.183 \AA{} for unirradiated samples to 5.200 \AA{} for samples irradiated to $5.0\ifmmode\times\else\texttimes\fi{}{10}^{19} \frac{n}{{\mathrm{cm}}^{2}}$. The results are discussed in terms of $A$-site occuptation in the ${A}_{3}B A\ensuremath{-}15$ structure and extrapolations of ${T}_{c}$ for complete order are considered.

Superconductivity and atomic ordering in neutron-irradiated Nb 3 Al

Superconducting A-15 compounds: A review

The effects of high energy (E > 1 MeV) neutron irradiation on the properties of Nb/sub 3/Ge prepared by chemical vapor deposition have been studied. Irradiation to a fluence of 3.4 x 10/sup 19/ n/cm/sup 2/ produces a decrease in the superconducting transition temperature T/sub c/ from 20.9 to 4.4 K and in the long-range order parameter S from 0.86 to 0.46, and an increase in the lattice parameter a/sub 0/ from 5.142 A to 5.174 A. For a fluence of 6.5 x 10/sup 19/ n/cm/sup 2/, most of the Nb/sub 3/Ge is transformed into a noncrystalline phase. The A15 phase is recovered after annealing.

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Superconductivity and atomic ordering in neutron-irradiated Nb/sub 3/Ge

Neutron irradiation of superconducting compounds

Electrical and optical properties of silicide single crystals and thin films

Large, reversible changes in the superconducting transition temperature ${T}_{c}$ of the Nb-based $A\ensuremath{-}15$ compounds ${\mathrm{Nb}}_{3}$Al, ${\mathrm{Nb}}_{3}$Sn, ${\mathrm{Nb}}_{3}$Ga, ${\mathrm{Nb}}_{3}$(Al, Ge), and ${\mathrm{Nb}}_{3}$Ge are observed when irradiated with high-energy ($Eg1$ MeV) neutrons at 60\ifmmode^\circ\else\textdegree\fi{}C. The transition widths of the irradiated samples are of the same order as the unirradiated samples and the original ${T}_{c}'\mathrm{s}$ are recovered by annealing. The results are discussed in terms of atomic ordering in the $A\ensuremath{-}15$ structure.

G. W. Webb

Papers

Atomic Ordering and Superconductivity in High-T c A-15 Compounds

Atomic ordering and superconductivity in high-T/sub c/ A-15 compounds