Ni/Te and Ni/Ag
2
Te interfacial reactions
Sinn-wen Chen
a, *
, Ting-ruei Yang
a
, Haw-wen Hsiao
b
, Po-han Lin
a
, Jia-hong Huang
b
,
Jenn-dong Huang
c
a
Department of Chemical Engineering, National Tsing Hua University, Taiwan
b
Department of Engineering and System Science, National Tsing Hua University, Taiwan
c
Material & Chemical Research Laboratory, Industrial Technology Research Institute, Taiwan
highlights
At 250
C and 200
C, the AgeNieTe isothermal sections are determined.
There are no ternary compounds in the AgeNieTe ternary system.
The reaction path is Ni/Ni
3
Te
2
/NiTe
0.775
/NiTe
2
/Te in the Ni/Te couples.
The reaction path is Ni/Ag/Ni
3
Te
2
/Ag
2
Te in the Ni/Ag
2
Te reaction couples.
article info
Article history:
Received 16 December 2015
Received in revised form
13 April 2016
Accepted 5 June 2016
Available online 11 June 2016
Keywords:
Interfacial reaction
Thermoelectric
Barrier layer
Ni
Ag
2
Te
abstract
Ag
2
Te is a promising thermoelectric compound, and Ni is commonly used as a barrier layer. The inter-
facial reactions in the Ni/Te and Ni/Ag
2
Te couples are examined at 200
C and 250
C. To illustrate the
reaction paths in the Ni/Ag
2
Te couples, the AgeNieTe isothermal sections at 200
C and 250
C are
determined based on experimental results of this study and related phase equilibria information. There is
no ternary compound phase found and the phase relationships are same at 200
C and 250
C. The
reaction paths of the two reaction couples are identical at these two temperatures. Three intermediate
phases, Ni
3
Te
2,
NiTe
0.775
and NiTe
2
, are formed in the Ni/Te couples. The reaction rate increases signifi-
cantly at 250
C, and is about six times higher than that at 200
C. Only the Ni
3
Te
2
and Ag phases are
observed in the Ni/Ag
2
Te couples. The reaction path is Ag
2
Te/Ni
3
Te
2
/Ag/Ni in the Ni/Ag
2
Te couples at both
200
C and 250
C.
© 2016 Elsevier B.V. All rights reserved.
1. Introduction
Ag
2
Te is a promising thermoelectric compound due to its low
thermal conductivity and high electronic mobility [1e4]. In ther-
moelectric devices there are usually numerous solder or braze
joints connecting arrays of thermoelectric modules. Barrier layers
between solders or brazes and thermoelectric materials are
required to avoid their direct contact and to prevent possible
interfacial reactions. Nickel is the most frequently used barrier layer
in these electronic solder joints, and is also used in thermoelectric
devices [5e10]. An understanding of the Ni/Ag
2
Te interfacial re-
actions is fundamentally important for the development of the
Ag
2
Te-base thermoelectric devices. It is found that there are no
significant reactions at the Ag/Ni contacts [11,12]. However, there
are no previous studies regarding the Ni/Te and Ni/Ag
2
Te interfacial
reactions. The Ni/Te and Ni/Ag
2
Te interfacial reactions at 200
C and
250
C are thus examined in this study. The isothermal sections of
the AgeNieTe at these temperatures are constructed to illustrate
the reaction paths.
2. Experimental procedures
The ternary AgeNieTe alloys and Te and Ag
2
Te substrates were
prepared with pure Ag shots (99.9 wt%, Alfa Aesar, War Hill, MA,
USA), Ni foil (99.9 wt%, Alfa Aesar, Ward Hill, MA, USA) and Te
pellets (99.9 wt%, Alfa Aesar, Ward Hill, MA, USA). Proper amounts
of pure constituent elements were weighed and encapsulated in
quartz tubes at 10
5
torr. vacuum. The sample capsules of
* Corresponding author.
E-mail address: swchen@mx.nthu.edu.tw (S.-w. Chen).
Contents lists available at ScienceDirect
Materials Chemistry and Physics
journal homepage: www.elsevier.com/locate/matchemphys
http://dx.doi.org/10.1016/j.matchemphys.2016.06.023
0254-0584/© 2016 Elsevier B.V. All rights reserved.
Materials Chemistry and Physics 180 (2016) 396e403