Cryst. Res. Technol. 43, No. 5, 537 – 541 (2008) / DOI 10.1002/crat.200711079

© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Wet-chemical synthesis and characterization of NiBi nano- and

micro-particles

I. M. Odeh1, S. Mahmoud

2, and G. P. Vassilev*

3

1 Yarmouk University, Physics Department, Irbid, Jordan 2 Yarmouk University, Chemistry Department, Irbid, Jordan 3 University of Plovdiv, Faculty of Chemistry, Plovdiv, Bulgaria

Received 19 September 2007, revised 5 December 2007, accepted 16 December 2007

Published online 1 February 2008

Key words transition metal alloys and compounds, X-ray diffraction, Ni–Bi intermediate phases.

PACS 81.05.Bx, 81.07.Wx, 81.16.Be

Preparation and characterization of NiBi nano- and micro-particles are presented. Firstly, predetermined

compositions were obtained by simultaneous precipitation from solutions of Bi(NO3)3 and Ni(NO3)2. The

precipitates were heated under oxygen flow and in air, and thereafter reduced to metals under hydrogen flow

at 673 K. Correlation between the predetermined and the actual compositions of the products was found.

Characterization of the precipitates was carried out employing X-ray diffraction, scanning and transmission

electron microscopy. Nickel-bismuth intermetallic phase (NiBi) particles with nano- and micro-dimensions

were observed in the samples after reduction. The other possible Ni–Bi intermediate phase (NiBi3) did not

form at these conditions although its presence was expected according to the phase diagram. This finding

might be useful for the implementation of Bi-based solders where the growth of the compound NiBi3 in the

solder joints must be prevented.

© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

1 Introduction

Nickel is one of the most common metallization materials in integrated circuit (IC) packages and its use is

expected to increase with the development of the advanced packaging technologies, such as the ball-grid-array

packaging [1–3]. The other component (Bi) of the studied materials is an important ingredient of many

prospective lead-free microelectronic solders [4–6]. Moreover, nickel–bismuth alloys are applied to control the

silicon steels kinetics of galvanizing [7] and are sought as bismuth suppliers in order to substitute lead in free-

machining steels [8].

As both, Ni and Bi, are constituents of forthcoming lead-free multicomponent systems, the system Ni–Bi

was included in the Thermodynamic database composed as contribution to the concerted European action

COST 531 [9]. In this aspect, experimental studies and thermodynamic optimization of this system have

recently been done by Vassilev et al. [6,10,11]. Moreover, Teyeb et al. [12] synthesized NiBi nanosized

particles using organic precursors but these are relatively expensive compared to the inorganic reagents. In this

view, the purpose of the present work is to study the possibility to synthesize nickel–bismuth nano- and micro-

sized particles by wet-chemistry methods using inorganic precursors.

2 Experimental

Aqueous solutions of Bi(NO3)3.5H2O and Ni(NO3)2.6H2O with appropriate concentrations were prepared. The

contents of nickel and bismuth (nickel versus bismuth) in these solutions had approximately the molar ratios

(MR) 4:1, 1:4, 1:3, 3:1 and 1:1 (Table 1, column MR). The numbers 1 to 5 (in the same order) were prescribed

to the respective samples obtained from these solutions. Their pH was adjusted to be inferior of 7 with 1 M ____________________

* Corresponding author: e-mail: gpvassilev@excite.com

538 I. M. Odeh et al.: NiBi nano- and micro-particles

© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.crt-journal.org

NaOH aqueous solution, then precipitation was achieved by adding concentrated solution of Na2CO3(aq) with

continuous stirring. The total masses of the precipitated hydroxides were around 10 g. The precipitates were

washed, dried and annealed under oxygen flow in order to decompose the eventual carbonates and to obtain

nickel and bismuth oxides only. Thereafter they were treated for 4 h at 673 K in hydrogen gas flow to reduce

nickel and bismuth ions to metals. The details of the procedures were the same as those applied to the synthesis

of Co–Bi micro- and nanoparticles reported freshly in [13].

Elemental analyses of the powders were done after the reduction process. They were carried out by atomic

absorption spectrometer (Analytic Gana 300AAF) for Ni and by ICP–OES, Varian Vista–AMPX apparatus –

for Bi and Ni. The scattering of the results was less than 1 at. % for each element. No special care against

possible secondary oxidation by air was taken.

X-ray diffraction (XRD) data of the powders were obtained by a computer controlled Philips PW1710/1050

Diffractometer. Morphology, microstructure and chemical analyses in microvolumes were performed by a

scanning electron microscope (SEM, FEI model QUANTA 200) equipped with an energy dispersive

spectrometer (EDX) and transmission electron microscope (TEM, Zeiss EM10CR). The samples for the SEM

analyses were prepared by spraying gently the powders onto graphite holder placed inside the apparatus.

3 Results and discussion

The chemical compositions of the master samples were determined by the spectral methods mentioned above

and are shown in table 1. As one can see, only rough correspondence between the atomic Ni:Bi ratios in the

aqueous solutions and in the precipitates was observed.

Table 1 Measured chemical compositions of the Ni–Bi master samples and the molar ratios (MR) of nickel

vs. bismuth in the initial solutions.

No Ni, at% Bi, at% MR

1 78 22 4:1

2 12 88 1:4

3 16 84 1:3

4 70 30 3:1

5 53 47 1:1

According to the Ni–Bi phase diagram [6,10] two intermetallic compounds NiBi and NiBi3 are stable at 673 K.

They melt peritectically at 919 and 738 K, respectively. The bismuth is liquid at this temperature because its

melting point is as low as 544.3 K (appr. 271 OC) [14]. Moreover, the compound NiBi3 and the liquid phase

consisting of almost pure bismuth are in equilibrium at 673 K in the system Ni–Bi. Nevertheless, it was found

by means of X-ray diffraction and scanning electron microscopy (SEM) studies, that the intermediate phase

NiBi3 did not form in the samples. It turned out that at 673 K the reaction (1) took place:

Nis + Biliq → NiBis (1)

Here the subscripts (s) and (liq) stay for solid and liquid phases, respectively.

The NiBi phase crystal structure has been determined initially by Hägg and Funke [15] using a specimen

with chemical composition of 45 at. % Bi. Later, Feschotte and Rosset [16] as well as Vassilev et al. [10,11]

have found that the compound NiBi is almost equiatomic. Further details are available in a number of

specialized handbooks [17–21]

The pure stable metallic phases: rhombohedral bismuth (Bi) and face-centered cubic nickel (fcc-Ni) were

identified following XRD data of JCPDS cards nos. 50519, and 4-850 and 45-1027, respectively, as well as

data of Mirkin [17]. Diffractograms of pure (Bi) and (Ni) specimens were done in order to get sampling for

comparison with the diffractograms of the bimetallic alloys.

It might be expected that bismuth oxides were not entirely reduced or a secondary air reduction might

occur. That is why care was taken to verify their presence in the specimens. Literature data [18] show that

various polymorphic modifications of the bismuth oxide exist (cards nos. 16-0654, 18-0244, 27-0049, 27-0050,

27-0051, 27-0052, 27-0054, 29-0236, 41-1449, 45-1344). The diffraction peaks of the bismuth oxide (Bi2O3)

found in the Co–Bi specimens [13], corresponded to the patterns given by JCPDS cards No. 29-0236 and No.

27-0050 (i.e. γ-Bi2O3) [18] with the most strongest peaks at 0.319 nm and 0.2737 nm (in that order).

Cryst. Res. Technol. 43, No. 5 (2008) 539

www.crt-journal.org © 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

We show in figure 1 the diffractograms of the five master samples (Table 1). In order to make the figure

more comprehensible the positions of the diffractograms Nos. 1–4 were shifted upright. Sketch-diffractogram

of the NiBi3 phase was plotted for comparison. The XRD data about this phase are taken from ref. [20] (Data

Sheet S1251713). Lee et al. [22] recently obtained similar NiBi3 diffraction pattern.

As one can see, the diffractograms of the specimens Nos. 1, 4 and 5, from one side, and these of Nos. 2 and

3 are similar by pairs (concerning the location of the strongest peaks). In the first three diffractograms (Nos. 1,

4 and 5) the strongest peaks belong to the phase NiBi (see Fig. 2a&b). In the samples Nos. 2 and 3 the

predominant phase is again NiBi, but Bi2O3 and (Bi) are also clearly present (Fig. 3).

Fig. 1 Experimental X-ray diffractograms (Cu Kα) of

the master samples: 1–5. The numbers of the curves

correspond to the numbers of the specimens. The curves

1–4 are shifted vertically by 5000 a.u. Sketch-

diffractogram (vertical segments) of the NiBi3 phase [22]

is plotted for comparison. The intensities of the

diffraction peaks (arbitrary units, a.u.) are plotted along

the ordinate, and the diffraction angles, 2Θ, (deg) are

plotted along the abscissa. (Online color at www.crt-

journal.org).

Fig. 2 a) X-ray diffractogram (line 1) of specimen No. 1 (47.10 at. % Bi). Sketch-diffractogram (vertical

segments) of the NiBi phase is plotted in order to illustrate its predominance. Experimental diffractogram of

Bi2O3 is shown for comparison. The intensity of the diffraction peaks (arbitrary units, a.u.) and the

diffraction angles (2Θ, deg) are plotted along the ordinate and the abscissa, respectively. b) X-ray

diffractogram (line 1) of specimen No. 1 (47.10 at. % Bi) where the NiBi phase is predominant.

Experimental diffractogram of pure nickel (Ni) and sketch-diffractogram (vertical segments) of the pure

bismuth phase (Bi) are shown for comparison. The intensity of the diffraction peaks (arbitrary units, a.u.)

and the diffraction angles (2 Θ, deg) are plotted along the ordinate and the abscissa, respectively. (Online

color at www.crt-journal.org).

Details of XRD data of specimen No. 1 are shown in figure 2 a&b. They are compared with literature

information or experimental diffractograms of Bi2O3, NiBi, (Ni) and (Bi) are shown. The diffractogram of

specimen No. 5 is not exhibited because it is quite similar to that of the sample No. 1 (see Fig. 1).

Clearly, the X-ray diffractogram of specimen No. 1 (as well as that one of specimen No. 5) corresponds to

the diffraction peaks system of the NiBi phase. The presence of some small quantities of Bi2O3 and of

unreacted (Bi) and (Ni) is plausible as well. It is of worth noting that the presence of Bi2O3 was more evident in

the X-ray diffractograms of Co–Bi specimens reported previously (see Fig. 2 in [13]) although it was not found

there by SEM. Thus, the X-rays diffractogram studies were found to be more sensible than the electron

540 I. M. Odeh et al.: NiBi nano- and micro-particles

© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.crt-journal.org

microprobe analyses. In figure 3 the diffractograms (found to be similar one to another) of the specimens Nos.

2 and 3 are exhibited. The diffractions peaks are marked with symbols, relating them with the respective

phases (i.e., NiBi, (Bi), Bi2O3). The phase (Ni) is not anticipated (either it was not observed) because the

specimens are bismuth-rich and all nickel should have reacted with the bismuth to form the compound NiBi.

Except the diffraction peaks of the latter compound (NiBi is the predominant phase) the presence of pure

bismuth phase (Bi) as well as of Bi2O3 was found. The interpretation of the diffractograms shown in figure 3 is

hindered, because many interlattice distances of the present phases are quite near one to another.

In figure 4 is exhibited SEM micrograph of specimen No. 3. The measurement of the composition by

electron microprobe analyses has shown that darker particles are Ni-rich (around 92 at. % Ni) while the lighter

crystals are Bi-rich (around 70 at. % Bi). As one can see no clear borders between dark and lighter areas were

observed. This might be explained by the circumstance that the system has not reached equilibrium state, due

to the short reaction-time.

Fig. 3 X-ray diffractograms (Cu Kα) of specimen

Nos. 2 and 3. The numbers of the curves correspond

to the numbers of the specimens. The diffraction

peaks of the phases identified in the samples (NiBi,

γ-Bi2O3, (Bi)) are marked as shown in the legend.

The intensity of the diffraction peaks (arbitrary

units, a.u.) and the diffraction angles (2 Θ, deg) are

plotted along the ordinate and the abscissa,

respectively. (Online color at www.crt-journal.org).

Fig. 4 SEM micrograph of specimen No. 3. The

darker particles are Ni-rich while the lighter crystals

are Bi-rich.

The solid-state kinetics of the interactions between nickel and bismuth was previously studied by Dybkov et al.

[23,24] in the temperature interval 150–250°C (423–523 K). The latter authors found that only NiBi3 layers

formed at the interface (Ni)/(Bi). Further, Lee et al. [22] investigated diffusion couples constituted by pure Ni

and NiBi3 and observed that NiBi layers grow (in the interval 330– 450°C (603–723 K). The phase

composition of the nickel–bismuth contact zone is important, because NiBi3 is soft and brittle, thus, its

formation could worsen the mechanical properties of the solder joints. In this connection, the finding that NiBi

phase forms by reaction of small solid Ni and liquid Bi particles could open a way to prevent the formation of

NiBi3 intermetallic layers in Ni and Bi containing lead-free solders.

4 Conclusions

Wet chemical method was applied to produce small Ni–Bi particles. Rough correspondence between the

atomic Ni:Bi ratios in the aqueous solutions and in the precipitates was observed. It was found that solid nickel

and liquid bismuth particles reacted to form NiBi phase during the reduction at 673 K. Thus, the compound

NiBi was identified in the samples, while the second Ni–Bi intermediate phase NiBi3 did not form at these

conditions. This finding might be useful for the implementation of Bi-based solders where the formation of the

compound NiBi3 is undesirable.

Cryst. Res. Technol. 43, No. 5 (2008) 541

www.crt-journal.org © 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Acknowledgements We would like to thank those who helped this work: namely, Dr.Y. Hamam and Dr. M.Rida (VSM),

Dr. I. Momani (ICP–OES), Dr. F Ababneh, W.Yousef (SEM), K.Mahafzah (AA), M. Khodor (TEM), I. Zayed, M.Jabali,

and A. Shehadeh (Workshop), and the Deanship of Higher Studies and Scientific Research at Yarmouk University, Jordan.

This work is related with the European COST action MP0602 (HISOLD).

References

[1] E. Bradley and K. Banerji, IEEE Trans. Compon. Pack. Manufact.Technol. B 19, 320 (1996).

[2] B. M. Romenesko, Int. J. Microcirc. Elec. Pack. 19, 64 (1996).

[3] Z. Mei, P. Gallery, D. Fisher, F. Hua, and J. Glazer, J. Adv. Elec. Pack. 2, 1543 (1997).

[4] C. Chen, C. Ho, A. Lin, and C. Kao, JEM 29, 51 (2000).

[5] W. Tao, C. Chen, C. Ho, W. Chen, and C. Kao, Chem. Mater. 13, 1051 (2001).

[6] G. Vassilev, J. Romanowska, and G. Wnuk, Intern. J. Mater. Res. 98, 468 (2007).

[7] R. Fratesi, N. Ruffini, M. Malavolta, and T. Bellezze, Surf. Coat. Techn. 157, 34 (2002).

[8] M. Iwase and A. McLean, Met. Trans. 14B, 765 (1983).

[9] COST 531, http://www.univie.ac.at/cost531/

[10] G. Vassilev, X. J. Liu, and K. Ishida, J. Phase Eq. Diff. 26, 161 (2005).

[11] G. Vassilev and K. Lilova, Cryst. Res. Technol. 42, 237 (2007).

[12] O.-E. Teyeb, J. Thurston, A. Kumar, M. Respaud, W. Guo, C. Weidenthaler, and K.. Whitmire, Chem. Mater. 17,

4750 (2005).

[13] I. Odeh, S. Mahmoud, and G. P. Vassilev, Int. J. Mater. Res. 98, 884 (2007).

[14] T. Massalski, “Binary Phase Diagrams”, Second Edition, ASM International, ASM CD-ROM, Ohio, USA (1996).

[15] G. Hägg and G. Funke, Z. Phys. Chem. B 6, 272 (1929). (in German)

[16] P. Feschotte and J. Rosset, J. Less-Com. Met. 143, 31 (1988). (in French)

[17] L. Mirkin, “Handbook of X-ray analyses of polycrystals”, GIFML, Moscow (1961) p. 863. (in Russian)

[18] JCPDS (Joint Committee on Powder Diffraction Standards) - ICDD (International centre for Diffraction Data),

http://www.icdd.com/, CD 1998.

[19] P. Villars (Ed.), “Pearson’s Handbook Desk Edition”, ASM International, 1997, ISBN 978-0-87170-603-4, OH,

USA.

[20] P. Villars (Editor in Chief), Pauling File Binaries Edition, Inorganic Materials Database and Design System, CD-

ROM, Germany, 2002, ISBN 3-00-009043-6.

[21] ICSD (Inorganic Crystal Structure Database), 2004, http://icsdweb.FIZ-Karlsruhe.de, card 58820.

[22] M. Lee, C. Chen, and C. Kao, Chem. Mater. 11, 292 (1999).

[23] O. Duchenko and V. Dybkov, J. Mater. Sci. Lett. 14, 1725 (1995).

[24] V. Dybkov and O. Duchenko, J. Alloys Comp. 234, 295 (1996).