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Experimental study of the 773 K isothermal section in the Ce–Ti–Si ternary system
Journal of Alloys and Compounds 496 (2010) 174–177
Contents lists available at ScienceDirect
Journal of Alloys and Compounds journal homepage: www.elsevier.com/locate/jallcom
Experimental study of the 773 K isothermal section in the Ce–Ti–Si ternary system Yongzhong Zhan ∗ , Xinjiang Zhang, Wenchao Yang, Chunhui Li 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 22 January 2010 Received in revised form 6 February 2010 Accepted 10 February 2010 Available online 18 February 2010 Keywords: Metals and alloys Phase diagrams X-ray diffraction Ce–Ti–Si alloys Isothermal section
a b s t r a c t The isothermal section at 773 K of the Ce–Ti–Si ternary system has been investigated by means of X-ray powder diffraction (XRD), differential thermal analysis (DTA) and scanning electron microscope–energy dispersive X-ray spectroscopy (SEM–EDX). The existences of 11 binary compounds, namely Ce5 Si3 , Ce3 Si2 , Ce5 Si4 , CeSi, Ce3 Si5 , CeSi2 , Ti3 Si, Ti5 Si3 , Ti5 Si4 , TiSi and TiSi2 have been confirmed. No ternary compound was found in this work. The results show that the phase equilibria consists of 14 single-phase regions, 25 binary phase regions and 12 ternary phase regions. The existence of the binary compound Ce5 Si3 with the Cr5 B3 -type crystal structure (space group: I4/mcm, a = 0.7890, c = 1.373) was experimentally confirmed. © 2010 Elsevier B.V. All rights reserved.
1. Introduction It is well known that the ternary compounds RE-TM-X (RE = rare earth, TM = transition metal, X = Si or Ge) exhibit some interesting properties such as heavy-fermion superconductivity, anomalous magnetism, Kondo behavior and/or intermediate valency [1–3]. Since phase diagrams are important basis for the research and application of materials, it is of importance to make clear the phase relationship of the RE-Ti–Si systems. In Refs. [4–8], the phase relation investigation of the (La, Nd, Pr, Gd and Dy)–Ti–Si ternary systems have been reported respectively by means of experimental methods. As a part of the systematic study, the investigation of the Ce–Ti–Si ternary system has not been reported yet. The binary systems bounding the Ce–Ti–Si ternary system have been described in detail in the previous literatures. In Ref. [9], the Ce–Ti phase diagram without intermediate compound was reported. Ti–Si binary phase diagram [10] shows five intermediate phases, i.e. Ti3 Si, Ti5 Si3 , Ti5 Si4 , TiSi and TiSi2 . Morozkin [8] did not absolutely confirm that Ti5 Si4 existed in the Dy–Ti–Si system at 1200 K. The Ce–Si binary phase diagram is given by Refs. [11,12]. The existence and the crystal structures of the compounds Ce5 Si3 , Ce3 Si2 , Ce5 Si4 , CeSi, Ce3 Si5 and CeSi2 were afforded. The structural data of the intermetallic compounds in the Ce–Ti–Si systems are given in Table 1.
∗ Corresponding author. Tel.: +86 771 3272311; fax: +86 771 3233530. E-mail address: [email protected] (Y. Zhan). 0925-8388/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2010.02.105
The purpose of the present work is to investigate experimentally the Ce–Ti–Si phase diagram by means of equilibrated alloy method, so as to provide essential information about the crystal structure of the intermetallic compounds and about the interaction of the components in the Ce–Ti–Si ternary system. 2. Experimental details Each sample was prepared to have a total weight of 2 g by weighing appropriate amounts of the pure components (Ce: 99.9 wt.%, Si: 99.99 wt.%, Ti: 99.99 wt.%). The alloy samples were produced in an electric arc furnace under an argon atmosphere using a non-consumable tungsten electrode and a water-cooled copper tray. The alloys were melted three times and turned around after melting in order to achieve complete fusion and homogeneous composition. The weight loss is less than 1% after melting. The samples were kept sealed in silica tubes in vacuum during homogenization. The heat treatment temperature of the samples was determined by differential thermal analysis (DTA) results of some typical ternary alloys or based on previous works of the three binary systems, i.e. Ce–Ti, Ce–Si and Ti–Si. The binary and ternary samples that contain more than 60% Ce were firstly annealed at 1023 K for 720 h, then cooled down to 773 K at a rate of 0.15 K/min, and finally kept at 773 K for 240 h. The other samples were firstly homogenized at 1173 K for 720 h, then cooled down to 773 K at a rate of 0.15 K/min, and finally kept at 773 K for 240 h. The cooling rate of 0.15 K/min was chosen to ensure complete solid state transition of the as annealed samples. Finally, all these annealed buttons were quenched in liquid nitrogen. X-ray powder diffraction (XRD) was used to determine the equilibria in the Ce–Ti–Si system. The XRD analysis was performed using a Rigaku D/Max 2500V diffractometer with Cu k␣ radiation and graphite monochromator operated at a voltage of 40 kV and a current of 200 mA. The scanning electron microscopy (SEM) with energy dispersive analysis (EDX) was used for microstructural analysis. The materials data were analyzed by using JADE 5.0 software [14] and PCW (Powder Cell Windows software) [15]. A Powder Diffraction File (PDF release 2002) was used to determine the phase existence in each sample.
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Table 1 Binary crystal structure data in the Ce–Ti–Si system. Phase
Composition, at.% Si
Structure type
Space group
Ce5 Si3 Ce3 Si2 Ce5 Si4 CeSi Ce3 Si5 CeSi2 Ti3 Si Ti5 Si3 Ti5 Si4 TiSi TiSi2
37.5 40 44.4 50 62.5 63.5–66.7 25 37.5 44.4 50 66.7
Cr5 B3 U3 Si2 Zr5 Si4 FeB ␣-GdSi2 ␣-ThSi2 TiP3 Mn5 Si4 Zr5 Si4 FeB TiSi2
I4/mcm P4/mbm P41 21 2 Pnma Imma I41 /amd P42/n P63/mcm P41 21 2 Pnma Fddd
3. Results and discussion 3.1. Phase analysis 3.1.1. Ce–Ti system In the Ce–Ti binary system, no binary compound was found in this work, which agreed well with the results of Ref. [9]. 3.1.2. Ti–Si system In the Ti–Si binary system, the phase diagram [10] shows five binary compounds, namely Ti3 Si, Ti5 Si3 , Ti5 Si4 , TiSi and TiSi2 . They were all experimentally confirmed at 773 K by analyzing the equilibrated samples. 3.1.3. Ce–Si system According to Ref. [11], six intermediate phases exist in the Ce–Si binary system, namely Ce5 Si3 , Ce3 Si2 , Ce5 Si4 , CeSi, Ce3 Si5 , CeSi and CeSi2 . At 773 K, they are confirmed in this work. For instance, the XRD pattern of the equilibrated sample containing 66.66 at.% Ce and 33.34 at.% Si clearly indicates the existence of a single-phase CeSi2 (Fig. 1). Furthermore, the XRD pattern and the SEM micrograph of the equilibrated sample containing 12 at.% Ce, 34 at.% Ti and 54 at.% Si clearly indicates the existence of three phases, i.e. CeSi2 , Ti5 Si4 and TiSi, as are shown respectively in Figs. 2 and 3. In Fig. 3, EDX result indicated that the black phase was Ti5 Si4 , the gray one was TiSi while the pale phase was CeSi2 . Another equilibrated sample containing 6 at.% Ce, 38 at.% Ti and 56 at.% Si consists of three phases CeSi2 , TiSi2 and TiSi, as indicated in Fig. 4. The microstructure of this sample examined by SEM and EDX clearly observed the three phases. EDX result indicated that the black phase was TiSi, the gray one was TiSi2 while the pale phase was CeSi2 , as is shown in Fig. 5.
Fig. 1. The XRD pattern of the equilibrated sample (66.66 at.% Ce and 33.34 at.% Si) indicating the existence of CeSi2 phase.
Lattice parameters (nm)
Reference
a
b
c
0.7890 0.779 0.795 0.829 0.4192 0.4192 1.0196 0.74610(3) 0.7133 0.657 0.8236(6)
– – – 0.396 0.413 – – – – 0.364 0.4773(4)
1.373 0.436 1.500 0.598 1.392 1.390 0.5097 0.51508(1) 1.2977 0.503 0.8523(6)
[12], this work [11,12] [11,12] [11,12] [11,12] [11,12] [13] [13] [13] [13] [13]
There is still considerable confusion in the crystallographic modifications of the compound Ce5 Si3 . Refs. [11,16] reported that Ce5 Si3 crystallized with the W5 Si3 -type and the Mn5 Si3 -type, respectively. Mayer and Shidlovsky [17] have reported that rare earth silicides RE5 Si3 crystallize with tetragonal Cr5 B3 -type for La to Nd but with hexagonal Mn5 Si3 -type for Sm to Lu except Eu. Furthermore, Ce5 Si3 was cited to be stable of the Cr5 B3 -type crystal structure in Refs. [17–19]. In this work, the XRD pattern of the equilibrated sample of the binary compound Ce5 Si3 containing 62.5 at.% Ce and 37.5 at.% Si is illustrated in Fig. 6. The analysis result using Jade 5.0 indicates that its crystal structure is Cr5 B3 -type structure. Its space group is I4/mcm and the lattice constants are a = 0.7890 nm, c = 1.373 nm.
Fig. 2. The XRD pattern of the sample (12 at.% Ce, 34 at.% Ti and 54 at.%Si) containing three phases CeSi2 , Ti5 Si4 and TiSi.
Fig. 3. The SEM micrograph of the sample containing 12 at.% Ce, 34 at.% Ti and 54 at.% Si.
176
Y. Zhan et al. / Journal of Alloys and Compounds 496 (2010) 174–177
Fig. 4. The XRD pattern of the sample (6 at.% Ce, 38 at.% Ti and 56 at.% Si) containing CeSi2 , TiSi2 and TiSi.
Fig. 7. The XRD pattern of the sample (40 at.% Ce, 24 at.% Ti and 36 at.% Si) containing Ce5 Si3 , Ti5 Si3 and Ce.
At 773 K, the binary compound Ce5 Si3 belonging to the Cr5 B3 -type crystal structure is confirmed. Moreover, the XRD pattern of the sample containing 40 at.% Ce, 24 at.% Ti and 36 at.% Si also clearly indicates the existence of Ce5 Si3 phase besides the Ti5 Si3 and Ce phases, as is shown in Fig. 7. 3.2. Isothermal section By analyzing 122 equilibrated samples, the isothermal section of the ternary Ce–Ti–Si system at 773 K was determined, which is shown in Fig. 8. XRD results confirm that 11 binary compounds,
Fig. 8. Isothermal section of the Ce–Ti–Si system at 773 K.
Fig. 5. The SEM micrograph of the sample containing 6 at.% Ce, 38 at.% Ti and 56 at.% Si.
namely Ce5 Si3 , Ce3 Si2 , Ce5 Si4 , CeSi, Ce3 Si5 , CeSi2 , Ti3 Si, Ti5 Si3 , Ti5 Si4 , TiSi and TiSi2 exist in this system at 773 K. Moreover, it is confirmed that no ternary compound exists in this work. The isothermal section consists of 14 single-phase regions, 25 twophase regions and 12 three-phase regions. Constitutions of the three-phase regions and compositions of the typical alloys are listed in Table 2. The solid solubility ranges of the single phases were determined using the phase-disappearing method and comparing the shift of the XRD patterns of the samples near to the compositions of the Table 2 Details of the three-phase regions and compositions of the typical alloys of the Ce–Ti–Si system at 773 K. Phase regions
Fig. 6. The XRD pattern of the equilibrated sample (62.5 at.% Ce and 37.5 at.% Si) indicating the existence of Ce5 Si3 phase.
1 2 3 4 5 6 7 8 9 10 11 12
Alloy composition (at.%) Ce
Ti
Si
10 6 12 16 12 26 22 46 30 40 10 16
10 38 34 32 40 20 36 12 32 24 60 74
80 56 54 52 48 54 42 42 38 36 30 10
Phase composition
TiSi2 + CeSi2 + Si TiSi2 + CeSi2 + TiSi Ti5 Si4 + CeSi2 + TiSi Ti5 Si4 + CeSi2 + Ti5 Si3 Ce3 Si5 + CeSi2 + Ti5 Si3 Ce3 Si5 + CeSi + Ti5 Si3 Ce5 Si4 + CeSi + Ti5 Si3 Ce5 Si4 + Ce3 Si2 + Ti5 Si3 Ce5 Si3 + Ce3 Si2 + Ti5 Si3 Ce5 Si3 + Ti5 Si3 + Ce Ti3 Si + Ti5 Si3 + Ce Ti3 Si + Ti + Ce
Y. Zhan et al. / Journal of Alloys and Compounds 496 (2010) 174–177
binary phases [20]. The results indicate that the compound Ti5 Si3 has a homogeneity range extending from about 37 to 38 at.% Si at 773 K, which has also been confirmed in our previous work [5,6], and the homogeneity range of CeSi2 stretches from 63.5 to 66.7 at.% Si. Moreover, the other intermediate compounds in the ternary Ce–Ti–Si system do not find a remarkable solid solution at 773 K. 4. Conclusion The isothermal section of the Ce–Ti–Si ternary system at 773 K has been determined using equilibrated alloy method for the first time. No ternary compound is found in this system. The isothermal section consists of 14 single-phase regions, 25 binary phase regions and 12 ternary phase regions. The following three-phase equilibria were observed, which were TiSi2 + CeSi2 + Si, TiSi2 + CeSi2 + TiSi, Ti5 Si4 + CeSi2 + TiSi, Ti5 Si4 + CeSi2 + Ti5 Si3 , Ce3 Si5 + CeSi2 + Ti5 Si3 , Ce3 Si5 + CeSi + Ti5 Si3 , Ce5 Si4 + CeSi + Ti5 Si3 , Ce5 Si4 + Ce3 Si2 + Ti5 Si3 , Ce5 Si3 + Ce3 Si2 + Ti5 Si3 , Ce5 Si3 + Ti5 Si3 + Ce, Ti3 Si + Ti5 Si3 + Ce, Ti3 Si + Ti + Ce. The existence of a binary compound Ce5 Si3 with the Cr5 B3 -type crystal structure (space group: I4/mcm, a = 0.7890, c = 1.373) was confirmed. Acknowledgements This work was supported by the National Natural Science Foundation of China (nos. 50761003, 50601006), the Key Project of China Ministry of Education (207085) and the Graduate Innovative Projects of Guangxi (no. 105930903091).
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References [1] Y.D. Seropegin, A.V. Gribanov, O.L. Kubarev, A.I. Tursina, O.I. Bodak, J. Alloys Compd. 317–318 (2001) 320–323. [2] A.V. Gribanov, Y.D. Seropegin, A.I. Tursina, O.I. Bodak, P. Rogl, H. Noël, J. Alloys Compd. 383 (2004) 286–289. [3] Y.D. Seropegin, B.I. Shapiev, A.V. Gribanov, O.I. Bodak, J. Alloys Compd. 288 (1999) 147–150. [4] Y. Zhan, Z. Yu, C. Li, Z. Sun, Y. Xu, Y. Wang, Y. Zhuang, J. Alloys Compd. 461 (2008) 128–131. [5] C. Li, Y. Zhan, J. Liu, Y. Du, Q. Gao, X. Li, J. Alloys Compd. 477 (2009) 274–277. [6] Y. Zhan, C. Li, J. Liu, Y. Du, H. Mo, J. Alloys Compd. 479 (2009) 201–203. [7] Y. Zhan, J. Ma, Z. Sun, Z. Hu, Y. Du, J. Alloys Compd. 475 (2009) 268–272. [8] A.V. Morozkin, J. Alloys Compd. 345 (2002) 155–157. [9] J. Zhang, L. Gao, W. Cao, J. Rare Earths 24 (2006) 182–187. [10] T.B. Massalski, H. Okamoto, P.R. Subramanian, L. Kacprzak (Eds.), Binary Alloy Phase Diagrams, vol. 2, 2nd ed., The Materials Information Society, Materials Park, OH, 1990, pp. 3099–3101, 3105–3108, 3367–3371. [11] A. Munitz, A.B. Gokhale, G.J. Abbaschian, Bull. Alloy Phase Diagrams 10 (1989) 73–78. [12] T.B. Massalski, P.R. Subramanian, H. Okamoto, L. Kacprzak, Binary Alloy Phase Diagrams, 2nd ed., ASM International, Materials Park, OH, USA, 1990. [13] P. Villars, Pearsons Handbook of Crystallographic Data, ASM International, Materials Park, OH, 1997, pp. 2842–2843, 2847. [14] Materials Data JADE Release 5.0, XRD Pattern Processing, Materials Data Inc., Livermore, CA, 2003. [15] Powder Cell for Windows, Version 2.4, 2000. [16] P. Villars, A. Prince, H. Okamato, Handbook of Ternary Alloy Phase Diagrams, ASM International, Materials Park, OH, USA, 1995. [17] I. Mayer, I. Shidlovsky, Inorg. Chem. 8 (1969) 1240. [18] E. Cordruwisch, D. Kaczorowski, P. Rogl, A. Saccone, R. Ferro, J. Alloys Compd. 320 (2001) 308–319. [19] D. Berthebaud, O. Tougait, M. Potel, H. Noel, J. Alloys Compd. 442 (2007) 104–107. [20] Y. Zhan, Y. Du, Y. Zhuang, in: J.-C. Zhao (Ed.), Methods for Phase Diagram Determination, first ed., Elsevier Science Press, Amsterdam, The Netherlands, 2007, pp. 108–150.
Contents lists available at ScienceDirect
Journal of Alloys and Compounds journal homepage: www.elsevier.com/locate/jallcom
Experimental study of the 773 K isothermal section in the Ce–Ti–Si ternary system Yongzhong Zhan ∗ , Xinjiang Zhang, Wenchao Yang, Chunhui Li 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 22 January 2010 Received in revised form 6 February 2010 Accepted 10 February 2010 Available online 18 February 2010 Keywords: Metals and alloys Phase diagrams X-ray diffraction Ce–Ti–Si alloys Isothermal section
a b s t r a c t The isothermal section at 773 K of the Ce–Ti–Si ternary system has been investigated by means of X-ray powder diffraction (XRD), differential thermal analysis (DTA) and scanning electron microscope–energy dispersive X-ray spectroscopy (SEM–EDX). The existences of 11 binary compounds, namely Ce5 Si3 , Ce3 Si2 , Ce5 Si4 , CeSi, Ce3 Si5 , CeSi2 , Ti3 Si, Ti5 Si3 , Ti5 Si4 , TiSi and TiSi2 have been confirmed. No ternary compound was found in this work. The results show that the phase equilibria consists of 14 single-phase regions, 25 binary phase regions and 12 ternary phase regions. The existence of the binary compound Ce5 Si3 with the Cr5 B3 -type crystal structure (space group: I4/mcm, a = 0.7890, c = 1.373) was experimentally confirmed. © 2010 Elsevier B.V. All rights reserved.
1. Introduction It is well known that the ternary compounds RE-TM-X (RE = rare earth, TM = transition metal, X = Si or Ge) exhibit some interesting properties such as heavy-fermion superconductivity, anomalous magnetism, Kondo behavior and/or intermediate valency [1–3]. Since phase diagrams are important basis for the research and application of materials, it is of importance to make clear the phase relationship of the RE-Ti–Si systems. In Refs. [4–8], the phase relation investigation of the (La, Nd, Pr, Gd and Dy)–Ti–Si ternary systems have been reported respectively by means of experimental methods. As a part of the systematic study, the investigation of the Ce–Ti–Si ternary system has not been reported yet. The binary systems bounding the Ce–Ti–Si ternary system have been described in detail in the previous literatures. In Ref. [9], the Ce–Ti phase diagram without intermediate compound was reported. Ti–Si binary phase diagram [10] shows five intermediate phases, i.e. Ti3 Si, Ti5 Si3 , Ti5 Si4 , TiSi and TiSi2 . Morozkin [8] did not absolutely confirm that Ti5 Si4 existed in the Dy–Ti–Si system at 1200 K. The Ce–Si binary phase diagram is given by Refs. [11,12]. The existence and the crystal structures of the compounds Ce5 Si3 , Ce3 Si2 , Ce5 Si4 , CeSi, Ce3 Si5 and CeSi2 were afforded. The structural data of the intermetallic compounds in the Ce–Ti–Si systems are given in Table 1.
∗ Corresponding author. Tel.: +86 771 3272311; fax: +86 771 3233530. E-mail address: [email protected] (Y. Zhan). 0925-8388/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2010.02.105
The purpose of the present work is to investigate experimentally the Ce–Ti–Si phase diagram by means of equilibrated alloy method, so as to provide essential information about the crystal structure of the intermetallic compounds and about the interaction of the components in the Ce–Ti–Si ternary system. 2. Experimental details Each sample was prepared to have a total weight of 2 g by weighing appropriate amounts of the pure components (Ce: 99.9 wt.%, Si: 99.99 wt.%, Ti: 99.99 wt.%). The alloy samples were produced in an electric arc furnace under an argon atmosphere using a non-consumable tungsten electrode and a water-cooled copper tray. The alloys were melted three times and turned around after melting in order to achieve complete fusion and homogeneous composition. The weight loss is less than 1% after melting. The samples were kept sealed in silica tubes in vacuum during homogenization. The heat treatment temperature of the samples was determined by differential thermal analysis (DTA) results of some typical ternary alloys or based on previous works of the three binary systems, i.e. Ce–Ti, Ce–Si and Ti–Si. The binary and ternary samples that contain more than 60% Ce were firstly annealed at 1023 K for 720 h, then cooled down to 773 K at a rate of 0.15 K/min, and finally kept at 773 K for 240 h. The other samples were firstly homogenized at 1173 K for 720 h, then cooled down to 773 K at a rate of 0.15 K/min, and finally kept at 773 K for 240 h. The cooling rate of 0.15 K/min was chosen to ensure complete solid state transition of the as annealed samples. Finally, all these annealed buttons were quenched in liquid nitrogen. X-ray powder diffraction (XRD) was used to determine the equilibria in the Ce–Ti–Si system. The XRD analysis was performed using a Rigaku D/Max 2500V diffractometer with Cu k␣ radiation and graphite monochromator operated at a voltage of 40 kV and a current of 200 mA. The scanning electron microscopy (SEM) with energy dispersive analysis (EDX) was used for microstructural analysis. The materials data were analyzed by using JADE 5.0 software [14] and PCW (Powder Cell Windows software) [15]. A Powder Diffraction File (PDF release 2002) was used to determine the phase existence in each sample.
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Table 1 Binary crystal structure data in the Ce–Ti–Si system. Phase
Composition, at.% Si
Structure type
Space group
Ce5 Si3 Ce3 Si2 Ce5 Si4 CeSi Ce3 Si5 CeSi2 Ti3 Si Ti5 Si3 Ti5 Si4 TiSi TiSi2
37.5 40 44.4 50 62.5 63.5–66.7 25 37.5 44.4 50 66.7
Cr5 B3 U3 Si2 Zr5 Si4 FeB ␣-GdSi2 ␣-ThSi2 TiP3 Mn5 Si4 Zr5 Si4 FeB TiSi2
I4/mcm P4/mbm P41 21 2 Pnma Imma I41 /amd P42/n P63/mcm P41 21 2 Pnma Fddd
3. Results and discussion 3.1. Phase analysis 3.1.1. Ce–Ti system In the Ce–Ti binary system, no binary compound was found in this work, which agreed well with the results of Ref. [9]. 3.1.2. Ti–Si system In the Ti–Si binary system, the phase diagram [10] shows five binary compounds, namely Ti3 Si, Ti5 Si3 , Ti5 Si4 , TiSi and TiSi2 . They were all experimentally confirmed at 773 K by analyzing the equilibrated samples. 3.1.3. Ce–Si system According to Ref. [11], six intermediate phases exist in the Ce–Si binary system, namely Ce5 Si3 , Ce3 Si2 , Ce5 Si4 , CeSi, Ce3 Si5 , CeSi and CeSi2 . At 773 K, they are confirmed in this work. For instance, the XRD pattern of the equilibrated sample containing 66.66 at.% Ce and 33.34 at.% Si clearly indicates the existence of a single-phase CeSi2 (Fig. 1). Furthermore, the XRD pattern and the SEM micrograph of the equilibrated sample containing 12 at.% Ce, 34 at.% Ti and 54 at.% Si clearly indicates the existence of three phases, i.e. CeSi2 , Ti5 Si4 and TiSi, as are shown respectively in Figs. 2 and 3. In Fig. 3, EDX result indicated that the black phase was Ti5 Si4 , the gray one was TiSi while the pale phase was CeSi2 . Another equilibrated sample containing 6 at.% Ce, 38 at.% Ti and 56 at.% Si consists of three phases CeSi2 , TiSi2 and TiSi, as indicated in Fig. 4. The microstructure of this sample examined by SEM and EDX clearly observed the three phases. EDX result indicated that the black phase was TiSi, the gray one was TiSi2 while the pale phase was CeSi2 , as is shown in Fig. 5.
Fig. 1. The XRD pattern of the equilibrated sample (66.66 at.% Ce and 33.34 at.% Si) indicating the existence of CeSi2 phase.
Lattice parameters (nm)
Reference
a
b
c
0.7890 0.779 0.795 0.829 0.4192 0.4192 1.0196 0.74610(3) 0.7133 0.657 0.8236(6)
– – – 0.396 0.413 – – – – 0.364 0.4773(4)
1.373 0.436 1.500 0.598 1.392 1.390 0.5097 0.51508(1) 1.2977 0.503 0.8523(6)
[12], this work [11,12] [11,12] [11,12] [11,12] [11,12] [13] [13] [13] [13] [13]
There is still considerable confusion in the crystallographic modifications of the compound Ce5 Si3 . Refs. [11,16] reported that Ce5 Si3 crystallized with the W5 Si3 -type and the Mn5 Si3 -type, respectively. Mayer and Shidlovsky [17] have reported that rare earth silicides RE5 Si3 crystallize with tetragonal Cr5 B3 -type for La to Nd but with hexagonal Mn5 Si3 -type for Sm to Lu except Eu. Furthermore, Ce5 Si3 was cited to be stable of the Cr5 B3 -type crystal structure in Refs. [17–19]. In this work, the XRD pattern of the equilibrated sample of the binary compound Ce5 Si3 containing 62.5 at.% Ce and 37.5 at.% Si is illustrated in Fig. 6. The analysis result using Jade 5.0 indicates that its crystal structure is Cr5 B3 -type structure. Its space group is I4/mcm and the lattice constants are a = 0.7890 nm, c = 1.373 nm.
Fig. 2. The XRD pattern of the sample (12 at.% Ce, 34 at.% Ti and 54 at.%Si) containing three phases CeSi2 , Ti5 Si4 and TiSi.
Fig. 3. The SEM micrograph of the sample containing 12 at.% Ce, 34 at.% Ti and 54 at.% Si.
176
Y. Zhan et al. / Journal of Alloys and Compounds 496 (2010) 174–177
Fig. 4. The XRD pattern of the sample (6 at.% Ce, 38 at.% Ti and 56 at.% Si) containing CeSi2 , TiSi2 and TiSi.
Fig. 7. The XRD pattern of the sample (40 at.% Ce, 24 at.% Ti and 36 at.% Si) containing Ce5 Si3 , Ti5 Si3 and Ce.
At 773 K, the binary compound Ce5 Si3 belonging to the Cr5 B3 -type crystal structure is confirmed. Moreover, the XRD pattern of the sample containing 40 at.% Ce, 24 at.% Ti and 36 at.% Si also clearly indicates the existence of Ce5 Si3 phase besides the Ti5 Si3 and Ce phases, as is shown in Fig. 7. 3.2. Isothermal section By analyzing 122 equilibrated samples, the isothermal section of the ternary Ce–Ti–Si system at 773 K was determined, which is shown in Fig. 8. XRD results confirm that 11 binary compounds,
Fig. 8. Isothermal section of the Ce–Ti–Si system at 773 K.
Fig. 5. The SEM micrograph of the sample containing 6 at.% Ce, 38 at.% Ti and 56 at.% Si.
namely Ce5 Si3 , Ce3 Si2 , Ce5 Si4 , CeSi, Ce3 Si5 , CeSi2 , Ti3 Si, Ti5 Si3 , Ti5 Si4 , TiSi and TiSi2 exist in this system at 773 K. Moreover, it is confirmed that no ternary compound exists in this work. The isothermal section consists of 14 single-phase regions, 25 twophase regions and 12 three-phase regions. Constitutions of the three-phase regions and compositions of the typical alloys are listed in Table 2. The solid solubility ranges of the single phases were determined using the phase-disappearing method and comparing the shift of the XRD patterns of the samples near to the compositions of the Table 2 Details of the three-phase regions and compositions of the typical alloys of the Ce–Ti–Si system at 773 K. Phase regions
Fig. 6. The XRD pattern of the equilibrated sample (62.5 at.% Ce and 37.5 at.% Si) indicating the existence of Ce5 Si3 phase.
1 2 3 4 5 6 7 8 9 10 11 12
Alloy composition (at.%) Ce
Ti
Si
10 6 12 16 12 26 22 46 30 40 10 16
10 38 34 32 40 20 36 12 32 24 60 74
80 56 54 52 48 54 42 42 38 36 30 10
Phase composition
TiSi2 + CeSi2 + Si TiSi2 + CeSi2 + TiSi Ti5 Si4 + CeSi2 + TiSi Ti5 Si4 + CeSi2 + Ti5 Si3 Ce3 Si5 + CeSi2 + Ti5 Si3 Ce3 Si5 + CeSi + Ti5 Si3 Ce5 Si4 + CeSi + Ti5 Si3 Ce5 Si4 + Ce3 Si2 + Ti5 Si3 Ce5 Si3 + Ce3 Si2 + Ti5 Si3 Ce5 Si3 + Ti5 Si3 + Ce Ti3 Si + Ti5 Si3 + Ce Ti3 Si + Ti + Ce
Y. Zhan et al. / Journal of Alloys and Compounds 496 (2010) 174–177
binary phases [20]. The results indicate that the compound Ti5 Si3 has a homogeneity range extending from about 37 to 38 at.% Si at 773 K, which has also been confirmed in our previous work [5,6], and the homogeneity range of CeSi2 stretches from 63.5 to 66.7 at.% Si. Moreover, the other intermediate compounds in the ternary Ce–Ti–Si system do not find a remarkable solid solution at 773 K. 4. Conclusion The isothermal section of the Ce–Ti–Si ternary system at 773 K has been determined using equilibrated alloy method for the first time. No ternary compound is found in this system. The isothermal section consists of 14 single-phase regions, 25 binary phase regions and 12 ternary phase regions. The following three-phase equilibria were observed, which were TiSi2 + CeSi2 + Si, TiSi2 + CeSi2 + TiSi, Ti5 Si4 + CeSi2 + TiSi, Ti5 Si4 + CeSi2 + Ti5 Si3 , Ce3 Si5 + CeSi2 + Ti5 Si3 , Ce3 Si5 + CeSi + Ti5 Si3 , Ce5 Si4 + CeSi + Ti5 Si3 , Ce5 Si4 + Ce3 Si2 + Ti5 Si3 , Ce5 Si3 + Ce3 Si2 + Ti5 Si3 , Ce5 Si3 + Ti5 Si3 + Ce, Ti3 Si + Ti5 Si3 + Ce, Ti3 Si + Ti + Ce. The existence of a binary compound Ce5 Si3 with the Cr5 B3 -type crystal structure (space group: I4/mcm, a = 0.7890, c = 1.373) was confirmed. Acknowledgements This work was supported by the National Natural Science Foundation of China (nos. 50761003, 50601006), the Key Project of China Ministry of Education (207085) and the Graduate Innovative Projects of Guangxi (no. 105930903091).
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