Significant improvement of Jc and flux pinning force of MgB2 by doping NTE-ZrW2O8 particles

• ZrW 2 O 8 doped MgB 2 was firstly synthesized with solid-state reaction method. • ZrW 2 O 8 doping significantly enhances J c of MgB 2 by inducing thermal strains. • Best J c @(4.2 K,5T) of doped sample is 4.1 × 10 4 A/cm 2 , 105 % of the undoped one. • Doping ZrW 2 O 8 does not significantly change the flux pinning type of MgB2. Although introducing second phase particles as additional pinning centers is an effective method to improve the current carrying capacity of MgB 2 , the thermal strain caused by second phase particles in MgB 2 and their impact on flux pinning have not received much attention. In this paper, flux pinning behavior of the thermal strain induced by the second phase particles in the MgB 2 bulk materials was studied by doping ZrW 2 O 8 particles which have negative thermal expansion (NTE) characteristics. Due to the significant difference in thermal expansion characters between ZrW 2 O 8 and MgB 2 , drastic thermal strain was induced in the lattice of MgB 2 by doping the NTE-ZrW 2 O 8 particles. These strains work as additional flux pinning centers and significantly enhance the irreversibility field, H irr , and critical current density, J c , of the MgB 2 . Taking J c as an example, at 4.2 K and 5 T, its J c value reaches 4.1 × 10 4 A/cm 2 , which is a 105 % performance improvement compared to the 2.0 × 10 4 A/cm 2 of the pure MgB 2 sample W-0; at 20 K and 2 T, its J c also reaches 1.3 × 10 5 A/cm 2 , which is 1.78 times of the 7.3 × 10 4 A/cm 2 for the pure MgB 2 sample under the same conditions. It is interesting that doping ZrW 2 O 8 does not significantly change the scaling behavior of the pinning force, indicating that the lattice strain work like surficial pinning center, while the point defect pinning center initiated by ZrW 2 O 8 particles themselves may only contribute to the high field region, causing the peak in the pinning force scaling curve to shift towards higher fields.