High Upper Critical Field of Sm0.85Nd0.15FeAsO0.85F0.15 Superconductors by Mechanical Alloying Synthesis

doi:10.3724/SP.J.1077.2012.11705

Abstract

Abstract:

High quality iron-based superconductors of Sm_0.85Nd_0.15FeAsO_0.85F_0.15 were reproducibly synthesized from highly reactive powders prepared by mechanical alloying method. The samples show T_c around 51 K, with an upper critical field (H_c2) up to 377 T determined from WHH formula, which is much higher than those found in the samples prepared from conventional solid state reactions (< 200 T). The high H_c2 is closely correlated with its microstructure. It is proposed that the mechanically alloyed raw materials contained high densities of lattice distortions, which were partially maintained during rapid heating and low temperature sintering, thus contributing to flux pinning in the final fine-grain ceramics.

Key words: iron-based superconductor, high upper critical field, mechanical alloying, low-temperature sintering

CLC Number:

TM263

FANG Ai-Hua, XIE Xiao-Ming, HUANG Fu-Qiang, JIANG Mian-Heng. High Upper Critical Field of Sm_0.85Nd_0.15FeAsO_0.85F_0.15 Superconductors by Mechanical Alloying Synthesis[J]. Journal of Inorganic Materials, 2012, 27(4): 439-444.

Figures/Tables 8

Fig. 1 Powder XRD patterns of the Sm0.85Nd0.15FeAsO0.85F0.15 sintered in different condition from MA powders

Table 1 Superconducting properties of Sm0.85Nd0.15FeAsO0.85F0.15 sintered at different conditions: critical temperature Tc, upper critical field Hc2, slope of temperature dependence of critical field dH/dT near Tc using the criteria of ρ90%, normal state resistivity ρ300K, normal-state residual resistivity ratio RRR = ρ300K/ρ55K

Sample	T_c/K	-dH_90%/dT (T·K^-1)	H_c2/ T	ρ_300K/ (mΩ·cm)	RRR	FWHM₍₁₀₂₎/(°)
1193 K-40 h	50.1	10.8	375	4.71	4.0	/
1253 K-20 min	51.4	10.2	363	2.44	3.8	0.108
1253 K-2 h	51.3	10.6	377	2.66	4.1	0.099
1253 K-12 h	51.9	10.2	367	1.99	4.3	0.092
1253 K-40 h	50.3	10.3	359	1.05	4.1	0.075
1433 K-20 min	49.0	8.7	295	2.90	3.6	/
1433 K-2 h	50.1	8.0	278	4.53	3.5	0.085
1433 K-40 h	50.4	7.7	272	0.47	3.8	0.070
1253 K-2 h*	46.9	7.1	215	5.55	3.1	/
1253 K-40 h*	49.8	6.6	228	0.83	3.6	0.069

Fig. 2 (a) Temperature dependent of resistivity of Sm0.85Nd0.15FeAsO0.85F0.15 samples sintered at different temperatures for 40 h from mechanical alloyed powders. (b) Temperature dependent of resistivity of Sm0.85Nd0.15FeAsO0.85F0.15 sample sintered at 1253 K for 40 h under different magnetic field. The inset shows the critical field vs Tc curve

Table 2 Typical critical temperature Tc (K) and upper critical field Hc2(0) (T) of SmFeAsO-based superconductors synthesized by using different methods

Sample	Synthesis condition	T_c/K	H_c2(0)/T	Remark
Sm_0.85Nd_0.15FeAsO_0.85F_0.15	1253 K, 2 h	51.3	377	MA, current study
SmFeAsO_0.85F_0.15^[13]	1433 K, 40 h	46	150	Solid state synthesis
SmFeAsO_0.65F_0.35^[14]	1433 K, 40 h	52	120	Solid state synthesis
SmFeAsO_0.85^[15]	1523 K, 2 h, 6 GPa	53.5	340^*	High pressure sintering

Fig. 3 SEM images of Sm0.85Nd0.15FeAsO0.85F0.15 sample sintered at 1253 K for 20 min to 40 h from mechanical alloyed powders

Fig. 4 EDS images of the Sm0.85Nd0.15FeAsO0.85F0.15 sample sintered at 1253 K for 40 h

Fig. 5 (a)-(d) SEM images of Sm0.85Nd0.15FeAsO0.85F0.15 sample sintered at 1253 K ranged from 20 min to 40 h from unmilled powders. (e)-(f) SEM images of Sm0.85Nd0.15FeAsO0.85F0.15 sample sintered for 40 h at different temperatures from unmilled powders

Fig. 6 (a) TEM image of the sample 1253 K-40 h, the inset shows the related diffraction pattern. (b) HRTEM image of the grain boundary in (a)

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