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参考文献

1 Introduction▲
2 Experimental▲
3 Results and discussion▲
3.1 Structural analysis
3.2 Electronic transport properties
3.3 Magnetic performance
4 Conclusion▲
图表▲

Rare Metals2017年第11期

Electronic transport and magnetic performance of Ni-Nb-Zr metallic glasses

Hai-Bin Wang Qing Wang Chong-Lin Chen Chuang Dong

School of Materials Science and Engineering, Jiangsu University of Science and Technology

School of Materials Science and Engineering, Dalian University of Technology

Department of Physics and Astronomy,University of Texas at San Antonio

收稿日期：14 February 2014

基金：financially supported by the National Natural Science Foundation of China (No.51171035);the Doctor Research Start-Up Funding of Jiangsu University of Science and Technology (No.1062921406);

Electronic transport and magnetic performance of Ni-Nb-Zr metallic glasses

Hai-Bin Wang Qing Wang Chong-Lin Chen Chuang Dong

School of Materials Science and Engineering, Jiangsu University of Science and Technology

School of Materials Science and Engineering, Dalian University of Technology

Department of Physics and Astronomy,University of Texas at San Antonio

Abstract：

The electronic transport and magnetic performances of Ni-Nb-Zr metallic glasses under low temperature were investigated. X-ray diffraction(XRD) analysis indicates that the Ni-Nb-Zr ribbons prepared by induction melting and melt spinning method have single amorphous phase. The electrical transport property results of these metallic glass alloys indicate that the Ni-Nb-Zr metallic glasses have negative resistivity temperature coefficients(RTC) and lowtemperature drift. The negative RTC and corresponding possible values of Fermi energy of Ni-Nb-Zr metallic glasses are interpreted by the extended Ziman-Faber diffraction theory.The magnetic measurements indicate that the magnetic intensities of the Ni-Nb-Zr metallic glasses are related to Ni content and atomic sizes while the low temperature has few influences on the magnetic properties.

Keyword：

Metallic glass; Electrical resistance; Magnetic properties;

Author： Hai-Bin Wang haibin666666@163.com;

Received： 14 February 2014

1 Introduction

Since the discovery of quasicrystals by Shechtman,amorphous and quasicrystalline materials of metastable phase alloys have been rapidly developed [ 1, 2, 3, 4] .Recently,Nibased metallic glasses have attracted great attention due to their excellent mechanical and chemical properties [ 5, 6, 7, 8, 9] .Ni-Nb and Ni-Zr systems such as Ni-Nb-Sn alloys [ 7] and Ni-Zr-Y-Al alloys [ 10] were found to have good glassforming ability (GFA) and better mechanical properties than traditional Ni-based metallic glasses.The goldschmidt atomic radii of Ni,Nb,and Zr are 0.128,0.146,and0.160 nm,respectively,which is in good agreement with Miracle'efficient cluster packing model [ 11] .As the result,the ternary Ni-Nb-Zr system becomes a good candidate for the development of new Ni-base bulk metallic glass (BMGs) with higher GFA and better mechanical properties.

In the ternary Ni-Nb-Zr phase diagram,many metallic glass compositions were found [ 9, 12] .Yamaura et al. [ 13] reported the fabrication of a 20-mm-width and 40-μmthickness ribbon with (Ni_0.6Nb_0.4)_100-xZr_x (x=0,20,30,40,and 50;at%) to study the hydrogen permeation.It was found that the permeability of the Ni-Nb-Zr amorphous alloys significantly increased with Zr content and temperature.The recent research [ 14] using the cluster-plusglue-atom model [ 15, 16] and a eutectic-related binary cluster M-Ni₆Nb₆ (M=0.5 Ni+0.5 Nb) derived from a eutectic phase Ni₇Nb₆ (Fe₇W₆ type) shows that the alloy rods with 3 mm in diameter and single glassy phase of these compositions are successfully achieved.A series of the new chemical compositions of[M-Ni₆Nb₄MZr]Ni₃alloys were designed,such as[M-Ni₆Nb_5-xMZr_x]Ni₃(x=0.76,0.84,0.92,1.00,1.08,1.16).In addition to the studies of mechanical properties and chemical stability of these new types of metallic glasses,studies on electrical transport property of these metallic glasses show many interesting and anomalous physical phenomena [ 17, 18] .One of the most interesting phenomena is that such alloys with amorphous structure can have either a positive or a negative resistivity temperature coefficient (RTC).In this research,four different composition alloys were fabricated,including the Ni-rich composition Ni_63.29Nb_31.65Zr_5.06,two new designed compositions Ni_62.5Nb_32.75Zr_4.75 ([M-Ni₆Nb_4.24MZr_0.76]Ni₃) and Ni_62.5Nb_31.25Zr_6.25 ([M-Ni₆Nb₄MZr₁]Ni₃) using cluster-plus-glue-atom model [ 14] ,and one Zr-rich composition Ni₄₈Nb₃₂Zr₂₀ for the development of hydrogen permeation materials [ 13] .The resistances as the function of temperature were studied to understand the electronic transport behavior.Furthermore,the effects of compositions as well as temperature on the magnetic properties of these alloys were analyzed to fully understand the Ni-Nb-Zr metallic glasses.

2 Experimental

Master ingots with compositions of Ni63.29Nb31.65Zr5.06,Ni62.5Nb_32.75Zr_4.75 ([M-Ni₆Nb_4.24MZr_0.76]Ni₃),Ni_62.5Nb_31.25Zr_6.25([M-Ni₆Nb₄MZr₁]Ni₃),and Ni₄₈Nb₃₂Zr₂₀ were first prepared by arc melting the mixtures of the constituent elements under argon atmosphere.The purities of the elements are 99.99 wt%for Ni,99.99 wt%for Zr,and 99.95 wt%for Nb,respectively.The ingots were remelted three times to improve compositional homogeneity.Then,these master ingots were remelted by induction melting in a quartz tube,and ribbon samples with width of 2-3 mm and thickness of 20-30μm were produced by a single roller melting-spinning apparatus at a wheel surface velocity of 50 m·s^-1.X-ray diffraction (XRD) with Cu Kαradiation (λ=0.15406 nm) was employed to study the crystallinity of these alloys.The electrical resistances of these ribbons in the temperature range of77-293 K were measured by a standard four-point method using the Lake Shore 370 AC resistance bridge.Liquid nitrogen was used to cooling down the ribbons to 77 K.Magnetic measurements were taken using a Quantum design physical property measurement systems(PPMS-9 system) with a vibrating sample magnetometer(VSM) at room temperature and low temperature cooled by liquid helium.

3 Results and discussion

3.1 Structural analysis

Figure 1 shows the typical XRD patterns of the as-prepared Ni_63.29Nb_31.65Zr_5.06,Ni_62.5Nb₃_2.75Zr_4.75,Ni_62.5Nb_31.25Zr_6.25,and Ni₄₈Nb₃₂Zr₂₂ ribbons.The XRD patterns of the first three samples with richer Ni contents show wide diffused peaks near 42°and no detectable crystalline peaks,indicating that all of these three samples have fully amorphous phases.The lower Ni content alloy Ni₄₈Nb₃₂Zr₂₀ also has a fully amorphous phase,but its amorphous peak shifts left obviously due to its larger average atomic radius.

Fig.1 XRD patterns of Ni-Nb-Zr ribbons with different compositions

3.2 Electronic transport properties

The electrical resistances of the ribbon samples as a function of temperature are shown in Fig.2a.All ribbon samples of Ni-Nb-Zr alloys exhibit negative RTC over the entire temperature range of 77-293 K.As shown in Fig.2b,the magnitudes of the resistances increase by2.0%-3.5%from room temperature to the boiling point of liquid nitrogen.Using this formula,

where RTC_ave is the average resistivity temperature coefficient,R_max is the maximum resistance of a sample,R_min is its minimum resistance,andΔT is the temperature difference,their average RTCs can be obtained:90×10^-6-162×10^-6 K^-1.The values are much smaller than those of most pure metals,such as Ni:～0.05 K^-1,Zr:～0.003 K^-1.and Pt:～0.002 K^-1 [ 19] .By means of heat treatment to produce part crystallization phase in metallic glass,it is possible to bring the value of RTC of ribbon metallic glasses further close to zero like BMGs [ 20] .So the ribbon samples of Ni-Nb-Zr metallic glasses possess the prospects to become candidate for low-temperature drift resistor used at low temperature because of their negative and small RTC.

Although various models were developed to understand the electric transport properties of metallic glasses,the Ziman-Faber diffraction model is usually adopted [ 21, 22, 23] by assuming a nearly free electron (NFE) model based on the Boltzmann equation.For metallic glasses containing transition elements,the formula of resistivity (ρ(T)) is as follows [ 24, 25, 26] :

Fig.2 Temperature dependence of resistance of Ni-Nb-Zr metallic glass ribbons in temperature range of 77-293 K a and ratio of resistances at boiling point of liquid nitrogen and room temperature b

where h is the reduced Planck constant,m is the mass of a electron,e is the electric charge of a electron,k_F is the Fermi wave number,E_F is the Fermi energy,Ωis the atomic volume,η₂(E_F) is the d-partial-wave phase shift describing the scattering of the conduction electrons by the ion cores which carry a muffin-tin potential centered on each ion position,S₀(2k_F) is the structure factor at T=0 K and scattering factor K=2k_F,and W is the DebyeWaller factor.

Using Eq.(2),the RTC can be got by taking derivatives ofρ(T) with respect to T.

For T≥θ_D,αis given by:

whereθ_D is the Debye temperature.This equation demonstrates thatαis negative if S_T(2k_F)>1.Therefore,the negative RTC of ribbon samples of Ni-Nb-Zr alloys means 2k_F lies in the vicinity of K_p,corresponding to K value at the first peak of structure factor S(K).More precisely,the negative RTC means the relative difference(η) between 2k_F and K_p,given by:

must satisfyη≤10%according to the extended ZimanFaber theory.

The width of the main Brillouin zone (K_p) can be obtained from XRD patterns using:

where 2θ_p is the Bragg diffraction angle corresponding to the first peak of structure factor S(K).Using Eqs.(5) and(6),the possible values of k_F and E_F of these Ni-Nb-Zr metallic glasses are calculated,as listed in Table 1.

3.3 Magnetic performance

Figure 3 shows the hysteresis M-H loops of the Ni-Nb-Zr ribbon samples under magnetic field up to 8×10⁵A·m^-1.The saturated moments are 0.175,0.125,0.050,and0.050 A·m²·kg^-1 under high magnetic field for the Ni-NbZr amorphous samples Ni_63.29Nb_31.65Zr_5.06,Ni_62.5Nb_32.75Zr_4.75,Ni_62.5Nb_31.25Zr_6.25,and Ni₄₈Nb₃₂Zr₂₀.

Although the Ni-rich metallic glass Ni_63.29Nb_31.65Zr_5.06has the highest saturated moment of 0.175 A·m²·kg^-1 among these Ni-Nb-Zr ribbon samples,it is still a weak magnetic substance compared with most Fe-and Co-based magnetic metallic glasses [ 27] of which the saturated moment is about60 A·m²·kg^-1.There are three major reasons for such low magnetic intensities of Ni-based metallic glass.First,among the three transition magnetic elements,Ni has the lowest atomic magnetic moment.Second,according to SlaterPauling rule [ 28, 29] of transition alloys,the average atomic magnetic moment is always shown as a function of the average atomic electron number.The electron numbers of Nb(41) and Zr(40) in Ni-Nb-Zr alloys are so large that highenergy electrons from Nb or Zr are likely to lower their energies and affect the 3d orbital of Ni.As a result,the average atomic magnetic moment is leveled.Among these Ni-Nb-Zr alloys,with the decrease in Ni content,the average atomic electron number decreases,so the decrease in magnetic intensities with Ni content decreasing is shown in Fig.3.The third reason is the decrease in exchange energy as a function of interatomic distance,causing low magnetic intensities of Ni-Nb-Zr metallic glasses.In the Ni-Nb-Zr system,the atomic radii of Nb and Zr are larger than that of Ni,while most of Fe-and Co-based magnetic metallic glasses contain some small-sized atoms,such as B.This phenomenon can also be found in Figs.3 and 4.For example,the Ni_62.5Nb_32.75Zr_4.75 ([M-Ni₆Nb_4.24MZr_0.76]Ni₃) and Ni_62.5Nb_31.25Zr_6.25 ([M-Ni₆Nb₄MZr₁]Ni₃) have same Ni content but show different magnetic properties.As Zr has a bigger atomic radius of 0.160 nm,the increase in Zr content could reduce the exchange interaction;consequently,the Ni_62.5Nb_31.25Zr_6.25 shows a lower magnetic intensity compared with Ni_62.5Nb_32.75Zr_4.75.Figure 4 shows the curves of intensity of magnetization with magnetic field intensity (M-H hysteresis loops) of the Ni_63.29Nb_31.65Zr_5.06 amorphous ribbon sample at 10,150,and 300 K.The saturated moment increases from 0.175 to 0.182 A·m²·kg^-1 with the decrease in temperature from 300 to 10 K.While the cold reduces the interatomic distance,the exchange interaction becomes stronger;consequently,the hysteresis M-H loops show a higher saturated moments at lower temperature.

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Table 1 Calculated values corresponding to relation of 2k_F and K_p

Fig.3 Magnetization curves of Ni-Nb-Zr samples under high magnetic field.Inset being detail of curves around origin of coordinates

Soft magnetic materials are defined as low coercivity(H_c<800 A·m^-1) and high permeability.As shown in the insets of Figs.3 and 4,they all exhibit high coercivities.The coercivity(Hc) of Ni_62.5Nb_32.75Zr_4.75,Ni_62.5Nb_31.25Zr_6.25,and Ni₄₈Nb₃₂Zr₂₀ are about 4000 A·m^-1,while that of Ni_63.29Nb_31.65Zr_5.06 is about 1000-2000 A·m^-1 at different temperatures.

Fig.4 Magnetization curves of Ni_63.29Nb_31.65Zr_5.06 at 10,150,and300 K.Inset being detail of curves around origin of coordinates

4 Conclusion

Ni-Nb-Zr ribbon samples with amorphous structure exhibit negative RTC in the temperature range of 77-293 K.Low-temperature drift with average RTC of 93×10^-6-162×10^-6 K^-1 demonstrates that the Ni-Nb-Zr metallic glasses possess the prospects to become candidate for lowtemperature drift resistor used at low temperature from room temperature to 77 K.

The magnetic intensities of Ni-Nb-Zr metallic glasses decrease with the increases in average atomic electron number and the interatomic distance.The Ni-rich metallic glass Ni_63.29Nb_31.65Zr_5.06 e×hibits the highest saturated moment of0.175 A·m²·kg^-1 and the lowest coercivity of 2000 A·m^-1among these Ni-Nb-Zr ribbon samples at 300 K.At 10 K,its s aturated moment reaches 0.182 A·m²·kg^-1 and its coercivity decreases to～1000 A·m^-1.

Acknowledgments This study was financially supported by the National Natural Science Foundation of China (No.51171035) and the Doctor Research Start-Up Funding of Jiangsu University of Science and Technology (No.1062921406).