Control of the Critical Current Density Through Microstructural Design by Ho2O3 and Te Co-addition into MgB2 Processed by Ex Situ Spark Plasma Sintering (original) (raw)

Superconductivity, 2019

Abstract

Dense samples with starting composition (MgB2)0.99(Tex(HoO1.5)y)0.01, x/y = 0/0, 0.73/027, 0.57/043, 0.4/0.6, 0.31/0.69, and 0.25/0.75 were processed by spark plasma sintering. Material is a bi-composite with a systematic microstructural change between “clean” and “dirty” MgB2 regions. The maximum self-field critical current density Jc0 and volume pinning force Fp, max are obtained for x/y = 0.4/0.66 = 0.67 where “clean” regions separate as isolated islands in a “dirty” matrix. The maximum value of Fp, max is high (9.2 GN/m3 at 5 K and 4.4 GN/m3 at 20 K). In the samples with x/y > 0.67 variation of the pinning-force-related parameters is small, while a decreasing x/y < 0.67 promotes a strong variation towards grain boundary pinning. In the curves of the pinning force vs. magnetic field, a shoulder occurs for a decreasing x/y (x/y < 0.67). Two pinning-behavior regimes can be defined, namely, below and above ∼25 K. When x/y decreases, variation of the midpoint critical temper...

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