Critical current density and superconducting parameters T<inf>c</inf>, H<inf>c2</inf>, and k in neutron-irradiated and annealed V<inf>3</inf>Si

Abstract

Single and polycrystalline V <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> Si was neutron irradiated at 240°C up to a fluence of 1.2 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">19</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> and subsequently isochronally annealed up to 1330°C. Measurements include the critical current density, j <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</inf> , the critical temperature, T <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</inf> , the upper critical field, H <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c2</inf> , and the residual resistance. Dislocation loops are identified by TEM as the part of the radiation induced defects responsible for j <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</inf> . Two different annealing temperatures are found for T <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</inf> and j <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</inf> , respectively. Due to the high irradiation temperature, T <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</inf> recovery occurs in one stage only, corresponding to thermally produced vacancles. All samples exhibit a scaling behavior of the volume pinning force between 0.9 and 0.6 reduced temperature. A j <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</inf> (H) peak is observed at low fluences and high annealing temperatures. The explanation for this behavior is based on a concentration dependent reduction of the theoretical threshold. A saturation behavior of the volume plnning force for high fluences and low annealing temperatures is observed, which is in quantitative agreement with the high-field mechanism of Kramers model above 0.8 reduced field. With these results we can explain the field dependent enhancement of j <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</inf> after neutron irradiation of A15 superconductors with grain boundary pinning.