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Phase equilibria of Gd–Sn–Te system at Te rich corner
Journal of Alloys and Compounds 475 (2009) 281–285
Contents lists available at ScienceDirect
Journal of Alloys and Compounds journal homepage: www.elsevier.com/locate/jallcom
Phase equilibria of Gd–Sn–Te system at Te rich corner Yongzhong Zhan ∗ , Jianbo Ma, Guanghua Zhang, Zhaohua Hu, Chunhui Li Key Laboratory of Nonferrous Metal Materials and New Processing Technology, Ministry of Education, Guangxi University, Nanning, Guangxi 530004, PR China
a r t i c l e
i n f o
Article history: Received 20 July 2008 Received in revised form 6 August 2008 Accepted 7 August 2008 Available online 21 September 2008 Keywords: Metals and alloys Phase diagrams X-ray diffraction
a b s t r a c t The method of synthesis of the Gd–Sn–Te system alloys as well as the phase equilibria have been described in this paper. Experimental results show that the samples have got phase equilibrium after heat treatment. In the isothermal section of Gd–Sn–Te ternary system at room temperature at Te rich corner(Te ≥ 50 at.%), 4 three-phase regions, i.e. Te + SnTe + GdTe3 , GdTe3 + SnTe + GdTe2 , Gd2 Te3 + SnTe + GdTe2 and Gd2 Te3 + (Sn,Gd)Te + GdTe are determined. The solubility of Gd in SnTe is about 11 at.%. The lattice parameters of Sn1−x Gdx Te (x = 0.02, 0.04, 0.06, 0.08 and 0.10) decrease with the increase of Gd content. © 2008 Elsevier B.V. All rights reserved.
1. Introduction Diluted magnetic semiconductors (DMSs) are semiconducting crystals whose lattice is made up in part of substitutional magnetic ions, and there have been considerable progress in the design and realization of DMSs. DMSs based on II–VI and III–V group compounds have been extensively investigated [1–3]. The development of magnetic semiconductors would be compatible with standard semiconductor technology and open new opportunities for various application. In recent years, it is found that the IV–VI group compound semiconductors, i.e. Sn–Te and Ge–Te system alloys possess some novel characteristics including magneto optical property, magneto transport, quickly write/clear reversible phase transformations optic storage, and ferromagnetism conduced by the RKKY (Ruderman–Kittel–Kasuya–Yoshida) exchange interaction of free carriers [4,5]. New magnetic and optic semiconductors in possession of perfect ordered ferromagnet can be obtained by normal preparation method such as magnetron sputtering, because the dielectric constant of IV–VI compound semiconductors is high. Due to the interplay of magnetism and semiconductor physics, the research of IV–VI DMS has attracted considerable attention and has been a hot spot of electronic materials and spintronics [6,7]. However, up to now few research on semiconductors doped with rare earth (RE) has been reported. Investigations on the rare earth-based DMS are just being carried out internationally. It should be pointed out that the lack of the basic data, such as phase diagram of the
∗ Corresponding author. Tel.: +86 771 3272311; fax: +86 771 3233530. E-mail address: [email protected] (Y. Zhan). 0925-8388/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2008.08.015
ternary system and crystal structure of the compounds, etc., has greatly impeded the researches of the rare earth-based DMS. The purpose of this work is to explore the synthesis method of the alloy samples of Gd–Sn–Te system and investigate the phase relation of this ternary system at room temperature at Te rich corner. For the Gd–Sn–Te system, the melting point of Gd (1311 ◦ C) is much higher than the melting point and boiling point of Te (Tm = 449.5 ◦ C, Tb = 989.8 ◦ C). Furthermore, the steam pressure of Te is so high that it is very easy to volatilize at high temperature. Therefore, when the alloys are melted by the routine electric arc furnace or high frequency furnace under pure argon atmosphere, the deflection of the composition would be large. In other words, it is difficult to synthesize Gd–Sn–Te system alloys with accurate composition through common smelting methods. In the present work, some of the samples were enveloped in the high-vacuum quartz tube, and then heated up by high frequency furnace. The other samples were prepared using a powder metallurgy method. The phase diagram of the Gd–Sn–Te system at room temperature at Te rich corner is constructed. The solid solubility of Gd in SnTe is determined by phase disappearing method and lattice parameter method. 2. Experimental details 2.1. Preparation of Gd–Sn–Te ternary alloys The Gd–Sn–Te ternary alloys were prepared by melting the high-vacuum enveloped materials with a high frequency furnace and by powder metallurgy. The details of the smelting experiment are as follows:
(1) Quartz tubes filled with high-purity Gd, Sn and Te (Gd: 99.9 wt.%, Sn: 99.9 wt.%, Te: 99.9 wt.%) were enveloped using acetylene–oxygen flame.
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Y. Zhan et al. / Journal of Alloys and Compounds 475 (2009) 281–285
Fig. 1. The samples prepared using high frequency furnace method. 36#: Gd 1 at.%, Sn 49 at.%, Te50%; 37#: Gd 2 at.%, Sn 48 at.%, Te 50%; and 38#: Gd 3 at.%, Sn 47 at.%, Te 50%. (2) The numbered samples were heated in the electrical resistance furnace at 500 ◦ C for 1 h, and then cooled down to room temperature spontaneously. (3) The samples filled in the high-vacuum quartz tubes were then heated up by high frequency furnace for several minutes. (4) The melted samples were annealed at 820 ◦ C for 2 h and then slowly cooled down at 1 ◦ C/h to 790 ◦ C for 48 h, and finally cool them down to 200 ◦ C for 5–15 days. Finally they were slowly cooled to room temperature. In this work, 16 equilibrated samples have been obtained. Each sample was prepared with a total weight of 2 g by weighing appropriate amounts of the pure components. 0.5 wt.% excess of Te over the stoichiometric composition was added in order to offset the volatilization of Te when the quartz tube was enveloped by acetylene–oxygen flame. Step 2 was carried out for two purposes. Firstly, the intermediate compound SnTe (with a boiling point higher than 989 ◦ C) may be synthesize at 500 ◦ C. Secondly, in this process the fragments of Sn, Te and SnTe will become an alloy button, which will envelop the element Gd after the quartz tube is heated at 500 ◦ C. Thus the samples may reach macrouniformity more easily in step 3. Powder metallurgy method was employed to prepare some of the samples that could not be melted through high frequency furnace or that difficult to get equilibrated. The starting materials were pure Gd and Sn powders and pure Te particles powdered in the carnelian mortar. Then the powders were mixed with required weight and compressed to cylinder buttons with diameter of 10 mm, using a desk-type powder tabletmachine. The cylinder buttons were enveloped in the high-vacuum quartz tube with inner diameter of 11 mm. Homogenization treatment was carried out at 400 ◦ C for 20–30 days. Finally, the samples were slowly cooled to room temperature.
Fig. 2. The patterns of the samples prepared through the powder metallurgy method. 51#: Gd 20 at.%, Sn 28 at.%, Te 52%; 52#: Gd 20 at.%, Sn 24 at.%, Te 56%; and 53#: Gd 17.5 at.%, Sn 20 at.%, Te 62.5%.
to merge as a whole. The buttons exhibit good appearance and metallic luster. Fig. 2 shows the pictures of the samples prepared by powder metallurgy method. Compact appearance that free of crack and macro-pore can be clearly seen. XRD analysis showed that most
2.2. Phase analysis The phase relationships in the Gd–Sn–Te system were determined by means of X-ray powder diffraction (XRD). The equilibrated alloys were analyzed at room temperature on a Rigaku D/Max 2500 V diffractometer with Cu K␣ ( = 0.154056 nm) radiation and graphite monochromator operated at 40 kV, 200 mA. The XRD data were collected by step scan. The most scanning area was between 20◦ and 60◦ , some of the scanning area was between 20◦ and 100◦ . The scan rate was 10◦ /min. The Materials Data Inc. software Jade 5.0 and Powder Diffraction File (PDF release 2002) were used for phase identification.
3. Result and discussion 3.1. Synthesis result of the alloys Some of the equilibrated samples prepared through the high frequency furnace method are shown in Fig. 1. It is clear that after heat treatment the inwall of the quartz tube is free of any volatile matter (the left sample). The starting materials have been smelted
Fig. 3. The isothermal section of the Gd–Sn–Te ternary system at room temperature at Te rich corner.
Table 1 Crystal structure data in the Sn–Te and Gd–Te binary system Compound
SnTe SnTe GdTe Gd2 Te3 GdTe2 GdTe2 Gd2 Te5 GdTe3 GdTe3
Space group
¯ Fm3m ¯ Fm3m ¯ Fm3m Pnma P4/nmm P4/mbm Cmcm Cmcm P42/n
Structure type
NaCl NaCl NaCl S3 Sb2 Cu2 Sb La4 Te7 Nd2 Te5 NdTe3 LaTe3
Lattice parameters (nm)
Reference
a
b
c
0.6315(1) 0.6328 0.6130 1.2009(9) 0.4317 0.910 0.4336(10) 0.4326 0.4321
– – – 0.43012(6) – – 4.36(1) 2.528 –
– – – 1.1818(2) 0.8951 0.930 0.4336(10) 0.4326 2.554
[9] [10] [9] [9] [9] [10] [9] [9] [10]
Y. Zhan et al. / Journal of Alloys and Compounds 475 (2009) 281–285
283
Fig. 4. The XRD patterns of some equilibrated Gd–Sn–Te ternary system samples: (a) Gd 17.5 at.%, Sn 20 at.% and Te 62.5 at.%; (b) Gd 20 at.%, Sn 24 at.% and Te 56 at.%; and (c) Gd 20 at.%, Sn 28 at.% and Te 52 at.%.
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Fig. 5. The XRD patterns of the equilibrated alloys of Sn1−x Gdx Te (x = 0.10, 0.12 and 0.14).
of the samples had got equilibrated state, which will be illustrated in Figs. 4–6.
3.2. Phase relations The binary phase diagram of Sn–Te shows that there is only one compound SnTe in this alloy system [8]. The crystal structure data of SnTe is shown in Table 1. The lattice parameter of SnTe confirmed in this work was different from that reported in Ref. [9], but agreed well with that in Ref. [10]. Five binary compounds, namely GdTe, Gd2 Te3 , GdTe2 , Gd2 Te5 and GdTe3 have been reported in Ref. [9]. The binary compounds GdTe, Gd2 Te3 , GdTe2 and GdTe3 were confirmed in this work. The crystal structure data of GdTe2 and GdTe3 determined in this work were same with the ones reported in Ref. [10]. However, the compound Gd2 Te5 was not found in this work. The equilibrated sample containing Gd 17.5 at.%, Sn 20 at.% and Te 62.5 at.% was composed of three phases GdTe3 , SnTe and GdTe2 , as shown in Fig. 4a. Gd2 Te5 phase cannot be detected in this equilibrated sample. The XRD patterns of the other samples at the three-phase region GdTe3 + SnTe + GdTe2 displayed the same result. The isothermal section of Gd–Sn–Te ternary system at room temperature at Te rich corner (Te ≥ 50 at.%) is shown in Fig. 3. Fig. 4b illustrated the XRD pattern of the equilibrated sample containing Gd 20 at.%, Sn 24 at.% and Te 56 at.%. It is obvious that there are three phases, i.e. Gd2 Te3 , SnTe and GdTe2 . Another equilibrated sample containing Gd 20 at.%, Sn 28 at.% and Te 52 at.% consists of three phases Gd2 Te3 , SnTe and GdTe, as indicated in the XRD pattern of Fig. 4c. As a result, the 2 three-phase regions Gd2 Te3 + SnTe + GdTe2 and Gd2 Te3 + SnTe + GdTe can be confirmed. In conclusion, based on the result of XRD test, 4 three-phase regions, i.e. Te + SnTe + GdTe3 , GdTe3 + SnTe + GdTe2 , Gd2 Te3 + SnTe + GdTe2 and Gd2 Te3 + (Sn,Gd)Te + GdTe are determined at the Te rich corner (Te ≥ 50 at.%). Correspondingly, 9 two-phase regions and 6 singlephase regions can be confirmed at the Te rich corner (Te ≥ 50 at.%). In this work, samples of Sn1−x Gdx Te (x = 0.02, 0.04, 0.06, 0.08, 0.1, 0.12, 0.14 and 0.16) were synthesized. The solid solubility of Gd in SnTe was determined by phase disappearing method and lattice parameter method. The results of XRD analysis showed that the solubility of Gd in SnTe was about 11 at.%, which was close to the data reported in Ref. [4]. There was only one phase observed in the sam-
Fig. 6. The lattice parameters of Sn1−x Gdx Te (x = 0.02, 0.04, 0.06, 0.08, 0.1, 0.12, 0.14 and 0.16).
ples of Sn1−x Gdx Te (x = 0.02, 0.04, 0.06, 0.08 and 0.10). However, another phase GdTe can be found in the samples of Sn1−x Gdx Te (x = 0.12, 0.14 and 0.16). The XRD patterns of Sn1−x Gdx Te (x = 0.10, 0.12 and 0.14) are shown in Fig. 5. The lattice parameters were then calculated by the method of extrapolation. Fig. 6 shows that the lattice parameters of Sn1−x Gdx Te (x = 0.02, 0.04, 0.06, 0.08 and 0.10) decrease almost linearly with increase of Gd content, while the lattice parameters of Sn1−x Gdx Te (x = 0.12, 0.14 and 0.16) keep constant. Therefore, it is concluded that the solubility of Gd in SnTe is about 11 at.%. 4. Conclusion The samples prepared by the method designed in this work have got phase equilibrium. The isothermal section of Gd–Sn–Te ternary system at Te rich corner at room temperature is determined. There are 4 three-phase regions, i.e. Te + SnTe + GdTe3 , GdTe3 + SnTe + GdTe2 , Gd2 Te3 + SnTe + GdTe2 and Gd2 Te3 + (Sn,Gd)Te + GdTe at the Te rich corner (Te ≥ 50 at.%). The solid solubility of Gd in SnTe is determined to be about 11 at.%, using
Y. Zhan et al. / Journal of Alloys and Compounds 475 (2009) 281–285
phase disappearing method and lattice parameter method. The lattice parameters of Sn1−x Gdx Te (x = 0.02, 0.04, 0.06, 0.08 and 0.10) decrease with the increase of Gd content. Acknowledgements The authors wish to express thanks to the financial support of the National Natural Science Foundation of China (50601006), the Key Project of China Ministry of Education (207085) and the Opening Foundation of State Key Laboratory of Powder Metallurgy (2007). References [1] T.M. Pekarek, D.J. Arenas, B.C. Crooker, I. Miotkowski, A.K. Ramdas, Magnetic measurements on ferromagnetic behavior in the bulk II–VI diluted magnetic semiconductor Zn1−x Crx Te, J. Appl. Phys. 95 (2004) 7178–7180.
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[2] H. Nojiri, Study of Mn doped II–VI and III–V DMS, Physica B: Cond. Matter 256 (1999) 569–572. [3] N. Kim, S.J. Lee, T.W. Kang, Study on phase transitions of III–Mn–V diluted magnetic semiconductor quantum wires, Phys. Lett. A 302 (2002) 341– 344. [4] T. Story, M. Górska, M. Arciszewska, E. Grodzicka, Z. Gołacki, R.R. Gałazka, Magnetic and electronic properties of Sn1−x Gdx Te, J. Magn. Magn. Mater. 140–144 (1995) 2041–2042. [5] Y. Fukuma, N. Nishimura, H. Asada, T. Koyanagi, Appearance of ferromagnetism by crystallizing a-Ge1−x Mnx Te film, Physica E 10 (1–3) (2001) 268–272. [6] Y. Fukuma, H. Asada, N. Nishimura, T. Koyanagi, Ferromagnetic properties of IV–VI diluted magnetic semiconductor Ge1−x Mnx Te films prepared by radio frequency sputtering, J. Appl. Phys. 93 (7) (2003) 4034–4039. [7] Y. Fukuma, H. Asada, J. Miyashita, N. Nishimura, T. Koyanagi, Magnetic properties of IV–VI compound GeTe based diluted magnetic semiconductors, J. Appl. Phys. 93 (10) (2003) 7667–7769. [8] R.C. Sharma, Y.A. Chang, Bull. Alloy Phase Diagrams 7 (1) (1986). [9] P. Villars, Pearson’s Handbook of Crystallographic Data, ASM International, Materials Park, OH, 1997, pp. 1970–1971, 2854. [10] Materials Data JADE Release 5.0, XRD Pattern Processing, Materials DaTa Inc., Livermore, CA, 2002.
Contents lists available at ScienceDirect
Journal of Alloys and Compounds journal homepage: www.elsevier.com/locate/jallcom
Phase equilibria of Gd–Sn–Te system at Te rich corner Yongzhong Zhan ∗ , Jianbo Ma, Guanghua Zhang, Zhaohua Hu, Chunhui Li Key Laboratory of Nonferrous Metal Materials and New Processing Technology, Ministry of Education, Guangxi University, Nanning, Guangxi 530004, PR China
a r t i c l e
i n f o
Article history: Received 20 July 2008 Received in revised form 6 August 2008 Accepted 7 August 2008 Available online 21 September 2008 Keywords: Metals and alloys Phase diagrams X-ray diffraction
a b s t r a c t The method of synthesis of the Gd–Sn–Te system alloys as well as the phase equilibria have been described in this paper. Experimental results show that the samples have got phase equilibrium after heat treatment. In the isothermal section of Gd–Sn–Te ternary system at room temperature at Te rich corner(Te ≥ 50 at.%), 4 three-phase regions, i.e. Te + SnTe + GdTe3 , GdTe3 + SnTe + GdTe2 , Gd2 Te3 + SnTe + GdTe2 and Gd2 Te3 + (Sn,Gd)Te + GdTe are determined. The solubility of Gd in SnTe is about 11 at.%. The lattice parameters of Sn1−x Gdx Te (x = 0.02, 0.04, 0.06, 0.08 and 0.10) decrease with the increase of Gd content. © 2008 Elsevier B.V. All rights reserved.
1. Introduction Diluted magnetic semiconductors (DMSs) are semiconducting crystals whose lattice is made up in part of substitutional magnetic ions, and there have been considerable progress in the design and realization of DMSs. DMSs based on II–VI and III–V group compounds have been extensively investigated [1–3]. The development of magnetic semiconductors would be compatible with standard semiconductor technology and open new opportunities for various application. In recent years, it is found that the IV–VI group compound semiconductors, i.e. Sn–Te and Ge–Te system alloys possess some novel characteristics including magneto optical property, magneto transport, quickly write/clear reversible phase transformations optic storage, and ferromagnetism conduced by the RKKY (Ruderman–Kittel–Kasuya–Yoshida) exchange interaction of free carriers [4,5]. New magnetic and optic semiconductors in possession of perfect ordered ferromagnet can be obtained by normal preparation method such as magnetron sputtering, because the dielectric constant of IV–VI compound semiconductors is high. Due to the interplay of magnetism and semiconductor physics, the research of IV–VI DMS has attracted considerable attention and has been a hot spot of electronic materials and spintronics [6,7]. However, up to now few research on semiconductors doped with rare earth (RE) has been reported. Investigations on the rare earth-based DMS are just being carried out internationally. It should be pointed out that the lack of the basic data, such as phase diagram of the
∗ Corresponding author. Tel.: +86 771 3272311; fax: +86 771 3233530. E-mail address: [email protected] (Y. Zhan). 0925-8388/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2008.08.015
ternary system and crystal structure of the compounds, etc., has greatly impeded the researches of the rare earth-based DMS. The purpose of this work is to explore the synthesis method of the alloy samples of Gd–Sn–Te system and investigate the phase relation of this ternary system at room temperature at Te rich corner. For the Gd–Sn–Te system, the melting point of Gd (1311 ◦ C) is much higher than the melting point and boiling point of Te (Tm = 449.5 ◦ C, Tb = 989.8 ◦ C). Furthermore, the steam pressure of Te is so high that it is very easy to volatilize at high temperature. Therefore, when the alloys are melted by the routine electric arc furnace or high frequency furnace under pure argon atmosphere, the deflection of the composition would be large. In other words, it is difficult to synthesize Gd–Sn–Te system alloys with accurate composition through common smelting methods. In the present work, some of the samples were enveloped in the high-vacuum quartz tube, and then heated up by high frequency furnace. The other samples were prepared using a powder metallurgy method. The phase diagram of the Gd–Sn–Te system at room temperature at Te rich corner is constructed. The solid solubility of Gd in SnTe is determined by phase disappearing method and lattice parameter method. 2. Experimental details 2.1. Preparation of Gd–Sn–Te ternary alloys The Gd–Sn–Te ternary alloys were prepared by melting the high-vacuum enveloped materials with a high frequency furnace and by powder metallurgy. The details of the smelting experiment are as follows:
(1) Quartz tubes filled with high-purity Gd, Sn and Te (Gd: 99.9 wt.%, Sn: 99.9 wt.%, Te: 99.9 wt.%) were enveloped using acetylene–oxygen flame.
282
Y. Zhan et al. / Journal of Alloys and Compounds 475 (2009) 281–285
Fig. 1. The samples prepared using high frequency furnace method. 36#: Gd 1 at.%, Sn 49 at.%, Te50%; 37#: Gd 2 at.%, Sn 48 at.%, Te 50%; and 38#: Gd 3 at.%, Sn 47 at.%, Te 50%. (2) The numbered samples were heated in the electrical resistance furnace at 500 ◦ C for 1 h, and then cooled down to room temperature spontaneously. (3) The samples filled in the high-vacuum quartz tubes were then heated up by high frequency furnace for several minutes. (4) The melted samples were annealed at 820 ◦ C for 2 h and then slowly cooled down at 1 ◦ C/h to 790 ◦ C for 48 h, and finally cool them down to 200 ◦ C for 5–15 days. Finally they were slowly cooled to room temperature. In this work, 16 equilibrated samples have been obtained. Each sample was prepared with a total weight of 2 g by weighing appropriate amounts of the pure components. 0.5 wt.% excess of Te over the stoichiometric composition was added in order to offset the volatilization of Te when the quartz tube was enveloped by acetylene–oxygen flame. Step 2 was carried out for two purposes. Firstly, the intermediate compound SnTe (with a boiling point higher than 989 ◦ C) may be synthesize at 500 ◦ C. Secondly, in this process the fragments of Sn, Te and SnTe will become an alloy button, which will envelop the element Gd after the quartz tube is heated at 500 ◦ C. Thus the samples may reach macrouniformity more easily in step 3. Powder metallurgy method was employed to prepare some of the samples that could not be melted through high frequency furnace or that difficult to get equilibrated. The starting materials were pure Gd and Sn powders and pure Te particles powdered in the carnelian mortar. Then the powders were mixed with required weight and compressed to cylinder buttons with diameter of 10 mm, using a desk-type powder tabletmachine. The cylinder buttons were enveloped in the high-vacuum quartz tube with inner diameter of 11 mm. Homogenization treatment was carried out at 400 ◦ C for 20–30 days. Finally, the samples were slowly cooled to room temperature.
Fig. 2. The patterns of the samples prepared through the powder metallurgy method. 51#: Gd 20 at.%, Sn 28 at.%, Te 52%; 52#: Gd 20 at.%, Sn 24 at.%, Te 56%; and 53#: Gd 17.5 at.%, Sn 20 at.%, Te 62.5%.
to merge as a whole. The buttons exhibit good appearance and metallic luster. Fig. 2 shows the pictures of the samples prepared by powder metallurgy method. Compact appearance that free of crack and macro-pore can be clearly seen. XRD analysis showed that most
2.2. Phase analysis The phase relationships in the Gd–Sn–Te system were determined by means of X-ray powder diffraction (XRD). The equilibrated alloys were analyzed at room temperature on a Rigaku D/Max 2500 V diffractometer with Cu K␣ ( = 0.154056 nm) radiation and graphite monochromator operated at 40 kV, 200 mA. The XRD data were collected by step scan. The most scanning area was between 20◦ and 60◦ , some of the scanning area was between 20◦ and 100◦ . The scan rate was 10◦ /min. The Materials Data Inc. software Jade 5.0 and Powder Diffraction File (PDF release 2002) were used for phase identification.
3. Result and discussion 3.1. Synthesis result of the alloys Some of the equilibrated samples prepared through the high frequency furnace method are shown in Fig. 1. It is clear that after heat treatment the inwall of the quartz tube is free of any volatile matter (the left sample). The starting materials have been smelted
Fig. 3. The isothermal section of the Gd–Sn–Te ternary system at room temperature at Te rich corner.
Table 1 Crystal structure data in the Sn–Te and Gd–Te binary system Compound
SnTe SnTe GdTe Gd2 Te3 GdTe2 GdTe2 Gd2 Te5 GdTe3 GdTe3
Space group
¯ Fm3m ¯ Fm3m ¯ Fm3m Pnma P4/nmm P4/mbm Cmcm Cmcm P42/n
Structure type
NaCl NaCl NaCl S3 Sb2 Cu2 Sb La4 Te7 Nd2 Te5 NdTe3 LaTe3
Lattice parameters (nm)
Reference
a
b
c
0.6315(1) 0.6328 0.6130 1.2009(9) 0.4317 0.910 0.4336(10) 0.4326 0.4321
– – – 0.43012(6) – – 4.36(1) 2.528 –
– – – 1.1818(2) 0.8951 0.930 0.4336(10) 0.4326 2.554
[9] [10] [9] [9] [9] [10] [9] [9] [10]
Y. Zhan et al. / Journal of Alloys and Compounds 475 (2009) 281–285
283
Fig. 4. The XRD patterns of some equilibrated Gd–Sn–Te ternary system samples: (a) Gd 17.5 at.%, Sn 20 at.% and Te 62.5 at.%; (b) Gd 20 at.%, Sn 24 at.% and Te 56 at.%; and (c) Gd 20 at.%, Sn 28 at.% and Te 52 at.%.
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Fig. 5. The XRD patterns of the equilibrated alloys of Sn1−x Gdx Te (x = 0.10, 0.12 and 0.14).
of the samples had got equilibrated state, which will be illustrated in Figs. 4–6.
3.2. Phase relations The binary phase diagram of Sn–Te shows that there is only one compound SnTe in this alloy system [8]. The crystal structure data of SnTe is shown in Table 1. The lattice parameter of SnTe confirmed in this work was different from that reported in Ref. [9], but agreed well with that in Ref. [10]. Five binary compounds, namely GdTe, Gd2 Te3 , GdTe2 , Gd2 Te5 and GdTe3 have been reported in Ref. [9]. The binary compounds GdTe, Gd2 Te3 , GdTe2 and GdTe3 were confirmed in this work. The crystal structure data of GdTe2 and GdTe3 determined in this work were same with the ones reported in Ref. [10]. However, the compound Gd2 Te5 was not found in this work. The equilibrated sample containing Gd 17.5 at.%, Sn 20 at.% and Te 62.5 at.% was composed of three phases GdTe3 , SnTe and GdTe2 , as shown in Fig. 4a. Gd2 Te5 phase cannot be detected in this equilibrated sample. The XRD patterns of the other samples at the three-phase region GdTe3 + SnTe + GdTe2 displayed the same result. The isothermal section of Gd–Sn–Te ternary system at room temperature at Te rich corner (Te ≥ 50 at.%) is shown in Fig. 3. Fig. 4b illustrated the XRD pattern of the equilibrated sample containing Gd 20 at.%, Sn 24 at.% and Te 56 at.%. It is obvious that there are three phases, i.e. Gd2 Te3 , SnTe and GdTe2 . Another equilibrated sample containing Gd 20 at.%, Sn 28 at.% and Te 52 at.% consists of three phases Gd2 Te3 , SnTe and GdTe, as indicated in the XRD pattern of Fig. 4c. As a result, the 2 three-phase regions Gd2 Te3 + SnTe + GdTe2 and Gd2 Te3 + SnTe + GdTe can be confirmed. In conclusion, based on the result of XRD test, 4 three-phase regions, i.e. Te + SnTe + GdTe3 , GdTe3 + SnTe + GdTe2 , Gd2 Te3 + SnTe + GdTe2 and Gd2 Te3 + (Sn,Gd)Te + GdTe are determined at the Te rich corner (Te ≥ 50 at.%). Correspondingly, 9 two-phase regions and 6 singlephase regions can be confirmed at the Te rich corner (Te ≥ 50 at.%). In this work, samples of Sn1−x Gdx Te (x = 0.02, 0.04, 0.06, 0.08, 0.1, 0.12, 0.14 and 0.16) were synthesized. The solid solubility of Gd in SnTe was determined by phase disappearing method and lattice parameter method. The results of XRD analysis showed that the solubility of Gd in SnTe was about 11 at.%, which was close to the data reported in Ref. [4]. There was only one phase observed in the sam-
Fig. 6. The lattice parameters of Sn1−x Gdx Te (x = 0.02, 0.04, 0.06, 0.08, 0.1, 0.12, 0.14 and 0.16).
ples of Sn1−x Gdx Te (x = 0.02, 0.04, 0.06, 0.08 and 0.10). However, another phase GdTe can be found in the samples of Sn1−x Gdx Te (x = 0.12, 0.14 and 0.16). The XRD patterns of Sn1−x Gdx Te (x = 0.10, 0.12 and 0.14) are shown in Fig. 5. The lattice parameters were then calculated by the method of extrapolation. Fig. 6 shows that the lattice parameters of Sn1−x Gdx Te (x = 0.02, 0.04, 0.06, 0.08 and 0.10) decrease almost linearly with increase of Gd content, while the lattice parameters of Sn1−x Gdx Te (x = 0.12, 0.14 and 0.16) keep constant. Therefore, it is concluded that the solubility of Gd in SnTe is about 11 at.%. 4. Conclusion The samples prepared by the method designed in this work have got phase equilibrium. The isothermal section of Gd–Sn–Te ternary system at Te rich corner at room temperature is determined. There are 4 three-phase regions, i.e. Te + SnTe + GdTe3 , GdTe3 + SnTe + GdTe2 , Gd2 Te3 + SnTe + GdTe2 and Gd2 Te3 + (Sn,Gd)Te + GdTe at the Te rich corner (Te ≥ 50 at.%). The solid solubility of Gd in SnTe is determined to be about 11 at.%, using
Y. Zhan et al. / Journal of Alloys and Compounds 475 (2009) 281–285
phase disappearing method and lattice parameter method. The lattice parameters of Sn1−x Gdx Te (x = 0.02, 0.04, 0.06, 0.08 and 0.10) decrease with the increase of Gd content. Acknowledgements The authors wish to express thanks to the financial support of the National Natural Science Foundation of China (50601006), the Key Project of China Ministry of Education (207085) and the Opening Foundation of State Key Laboratory of Powder Metallurgy (2007). References [1] T.M. Pekarek, D.J. Arenas, B.C. Crooker, I. Miotkowski, A.K. Ramdas, Magnetic measurements on ferromagnetic behavior in the bulk II–VI diluted magnetic semiconductor Zn1−x Crx Te, J. Appl. Phys. 95 (2004) 7178–7180.
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