机械合金化合成高临界场Sm0.85Nd0.15FeAsO0.85F0.15超导体

doi:10.3724/SP.J.1077.2012.11705

摘要/Abstract

摘要：

通过采用机械合金化方法制备的高活性的粉体, 可以高度可重复性地制备高质量的铁基超导材料Sm_0.85Nd_0.15FeAsO_0.85F_0.15. 样品具有高临界温度T_c(约51 K)和高临界场H_c2(达到377 T). 由WHH公式确定的H_c2显著高于常规固相方法制备样品的典型值(<200 T). 高的临界磁场H_c2与样品微结构有很大关系. 机械合金化处理的原始粉体包含大量的晶格畸变缺陷, 在快速升温和低温退火制备的小晶粒陶瓷样品中这些缺陷会部分残留, 因此形成有效的磁通钉扎, 从而提高样品的临界场.

关键词: 铁基超导体, 高临界场, 机械合金化, 低温烧结

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

中图分类号:

TM263

方爱华, 谢晓明, 黄富强, 江绵恒. 机械合金化合成高临界场Sm_0.85Nd_0.15FeAsO_0.85F_0.15超导体[J]. 无机材料学报, 2012, 27(4): 439-444.

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.

图/表 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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