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Thermal stability of the Pr3Pt4 compound
Journal of Alloys and Compounds 407 (2006) 112–114
Thermal stability of the Pr3Pt4 compound Z.F. Gu ∗ , G. Cheng, J. Ren Department for Information Materials Science and Engineering, Guilin University of Electronic Technology, Guilin 541004, P.R. China Received 24 January 2005; received in revised form 19 May 2005; accepted 2 June 2005 Available online 2 August 2005
Abstract The temperature stability of the Pr3 Pt4 compound was investigated by isothermal annealing at different temperatures, X-ray diffraction (XRD) and differential thermal analysis (DTA). It was found that the decomposition reaction Pr3 Pt4 → PrPt + PrPt2 took place at temperatures ranging approximately from 360 ◦ C to 830 ◦ C and it was an exothermal reaction. After annealing at 500–750 ◦ C for 7 days, the Pr3 Pt4 compound decomposes completely into the two neighboring compounds PrPt and PrPt2 . © 2005 Elsevier B.V. All rights reserved. Keywords: Rare earth alloys and compounds; X-ray diffraction; Phase transitions; Thermal analysis
1. Introduction
2. Experimental
According to the current version of the binary alloy phase diagrams and Pearson’s Handbook of Crystallographic Data for Intermetallic Phases [1,2], there exist seven binary compounds in the Pr–Pt binary system, namely PrPt5 (CaCu5 structure type), PrPt3 (Cu2 Mg structure type), PrPt2 (Cu2 Mg structure type), Pr3 Pt4 (Pd4 Pu3 structure type), PrPt (BFe structure type for ␣PrPt at low temperatures and CrB structure type for PrPt at high temperatures), Pr3 Pt2 (Er3 Ni2 structure type) and Pr7 Pt3 (Fe3 Th7 structure type), and the Pr3 Pt4 compound is formed in a peritectic reaction (L + PrPt Pr3 Pt4 ) at about 1620 ◦ C, which is similar to Nd3 Pt4 that is formed in a peritectic reaction (L + NdPt Nd3 Pt4 ) at 1420 ◦ C. Palenzona reported that the Pr3 Pt4 compound exists after annealing at 300 ◦ C for 5 days [3]. Our recent investigations confirmed that the Pr3 Pt4 compound exists as well after annealing at 900 ◦ C for 14 days [4]. However, it was surprising that Pr3 Pt4 does not exist in the Fe–Pt–Pr ternary alloys with more than 1 at.% Fe after annealing at 900 ◦ C for 14 days [4]. For this reason, a detailed investigation of the temperature stability of the Pr3 Pt4 compound is desirable and will be presented in this report.
The samples of the Pr3 Pt4 compound investigated were prepared by arc-melting of starting materials of at least 99.9% purity under purified argon. They were remelted four times to ensure good homogeneity. The mass losses after the melting were less than 0.5 wt.%. After arc-melting, the samples were sealed in quartz tubes pre-evacuated and refilled with some purified argon and then annealed under various conditions as listed in Table 1 and finally quenched in water. After annealing, the phase compositions of the samples were examined by powder X-ray diffraction (XRD) with Cu K␣ radiation over a 2θ angle from 20◦ to 60◦ . The differential thermal analysis (DTA) was carried out under purified nitrogen at a heating rate of 20 ◦ C/min from room temperature to 1000 ◦ C. The mass of the samples for the differential thermal analysis is 6–12 mg. The Pt/PtRh thermocouples of the DTA instrument were calibrated at the melting point of high-purity Al metal.
∗
Corresponding author. E-mail address: [email protected] (Z.F. Gu).
0925-8388/$ – see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2005.06.018
3. Results and discussion Results of X-ray diffraction measurements for the Pr3 Pt4 samples annealed at 900 ◦ C, 650 ◦ C and 300 ◦ C, respectively, are displayed in Fig. 1. The data at the top part and bottom part of Fig. 1 show that the Pr3 Pt4 annealed samples
Z.F. Gu et al. / Journal of Alloys and Compounds 407 (2006) 112–114
113
Table 1 Annealing conditions and phase compositions of Pr3 Pt4 samples Annealing conditions
Phase compositions
900 ◦ C
Annealed at for 14 days Annealed at 900 ◦ C for 14 days, then at 800 ◦ C for 7 days Annealed at 900 ◦ C for 14 days, then at 750 ◦ C for 7 days Annealed at 900 ◦ C for 14 days, then at 650 ◦ C for 7 days Annealed at 900 ◦ C for 14 days, then at 500 ◦ C for 7 days Annealed at 900 ◦ C for 14 days, then at 300 ◦ C for 7 days Annealed at 300 ◦ C for 5 days Annealed at 300 ◦ C for 5 days, then at 600 ◦ C for 1 day
and
Pr3 Pt4 + PrPt2 (small) PrPt + PrPt2 + Pr3 Pt4
and
PrPt + PrPt2
and
PrPt + PrPt2
and
PrPt + PrPt2
and
Pr3 Pt4 + PrPt2 (small)
and
Pr3 Pt4 + PrPt2 (small) PrPt + PrPt2
are approximately single phase Pr3 Pt4 except for a small amount of second phase PrPt2 and the crystal structure of the phase Pr3 Pt4 corresponds to the rhombohedral Pd4 Pu3 structure type. These results indicate clearly that the Pr3 Pt4 compound does exist at 900 ◦ C and 300 ◦ C, which is consistent with data reported in literature [3]. However, it is surprising that the Pr3 Pt4 phase does not exist in the sample annealed at 650 ◦ C for 7 days (intermediate part of Fig. 1). Only the other two phases PrPt and PrPt2 exist. Of the two phases, the former has the orthorhombic FeB structure type and the latter the cubic Cu2 Mg structure type. This suggests strongly that a decomposition reaction occurs at 650 ◦ C and the Pr3 Pt4 phase has completely transformed into the two neighboring phases PrPt and PrPt2 according to the reaction Pr3 Pt4 → PrPt + PrPt2 . Also those samples, which were annealed at 500 ◦ C, 600 ◦ C and 750 ◦ C for 7 days, respectively, consist of the two phases PrPt and PrPt2 according to the results obtained from their XRD data (see Table 1). This means that the decomposition reaction takes place as well at 500 ◦ C, 600 ◦ C and 750 ◦ C, which is totally the same as that at 650 ◦ C. However, the result of XRD obtained for the sample annealed at 800 ◦ C for 7 days reveals that it consists of the three phases Pr3 Pt4 , PrPt and PrPt2 . This implies that only
Fig. 1. XRD patterns of Pr3 Pt4 samples annealed at 900 ◦ C (top part), 650 ◦ C (intermediate part) and 300 ◦ C (bottom part), respectively.
Fig. 2. DTA curves of the Pr3 Pt4 sample annealed at 900 ◦ C, measured at a heating rate of 20 ◦ C/min, on 6 mg (top part) and 12 mg (bottom part) of powder samples, respectively.
part of Pr3 Pt4 has decomposed and transformed into PrPt and PrPt2 . From these observations mentioned above, it follows that the decomposition reaction occurs at least at 500–800 ◦ C and the reaction rate is different from temperature to temperature. The rate is slower at 800 ◦ C than at 500–750 ◦ C. All the phase compositions of the presently investigated Pr3 Pt4 samples are listed in Table 1. The differential thermal analysis curves measured on 6 mg (top part) and 12 mg (bottom part) of the Pr3 Pt4 powder samples, respectively, are displayed in Fig. 2. A large exothermic peak was observed at about 362 ◦ C at the top part of Fig. 2. It corresponds to the decomposition reaction Pr3 Pt4 → PrPt + PrPt2 . By contrast, a small endothermic peak around 830 ◦ C was observed at the bottom part of Fig. 2. This peak arises as a consequence of the composition reaction PrPt + PrPt2 → Pr3 Pt4 . Compared with the exothermic peak, the endothermic peak is much smaller, and is often too small to be observed (see top part of Fig. 2). The reason for this may be the fact that the composition reaction takes place on the boundary between the phase PrPt and PrPt2 and the course of the reaction involving atomic diffusion is impeded by the reaction product of Pr3 Pt4 . The occurrence of the composition reaction has been observed in an annealing experiment. The sample annealed at 600 ◦ C for 1 day is composed of the two phases PrPt and PrPt2 , whereas the same sample annealed at 1000 ◦ C for 10 days again is the three phases Pr3 Pt4 , PrPt and PrPt2 . These observations give further evidence that the decomposition reaction of the Pr3 Pt4 compound takes place at temperatures ranging approximately from 360 ◦ C to 830 ◦ C. Based on the experimental results of the presently investigated Pr3 Pt4 compound, we thus revise the respective part
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Z.F. Gu et al. / Journal of Alloys and Compounds 407 (2006) 112–114
4. Conclusions 1. The Pr3 Pt4 compound with the rhombohedral Pu3 Pd4 structure type is unstable and decomposes into the two neighboring compounds PrPt and PrPt2 at temperatures ranging approximately from 360 ◦ C to 830 ◦ C. 2. The decomposition reaction of the Pr3 Pt4 compound is an exothermic one with a large thermal effect and the reaction rate is faster at temperatures from 500 ◦ C to 750 ◦ C. 3. There exist two solid-state phase transformations for the Pr3 Pt4 compound upon cooling or heating, namely the eutectoid transition Pr3 Pt4 PrPt + PrPt2 at about 830 ◦ C and the peritectoid transition PrPt + PrPt2 Pr3 Pt4 at about 360 ◦ C.
Acknowledgement This work was supported by the National Natural Science Foundation of China (authorized number: 50261002). Fig. 3. Revised Pr–Pt phase diagram around the Pr3 Pt4 compound.
of the Pr–Pt phase diagram in the way shown in Fig. 3. With decreasing temperature, the Pr3 Pt4 compound is formed in a peritectic reaction (L + PrPt Pr3 Pt4 ) at about 1620 ◦ C and decomposes in a eutectoid reaction (Pr3 Pt4 PrPt + PrPt2 ) at about 830 ◦ C. When cooling to a temperature of about 360 ◦ C, the peritectoid reaction (PrPt + PrPt2 Pr3 Pt4 ) takes place and results in the combination of PrPt with PrPt2 to form Pr3 Pt4 .
References [1] T.B. Massalski (Ed.), Binary Alloy Phase Diagrams, second ed., ASM International, Materials Park, OH, 1990. [2] P. Villars, L.D. Calvert, Pearson’s Handbook of Crystallographic Data for Intermetallic Phases, ASM International, Materials Park, OH, 1991. [3] A. Palenzona, J. Less Common Met. 53 (1977) 133. [4] J. Ren, Z.F. Gu, G. Cheng, H.Y. Zhou, J. Alloys Compd. 394 (2005) 211–214.
Thermal stability of the Pr3Pt4 compound Z.F. Gu ∗ , G. Cheng, J. Ren Department for Information Materials Science and Engineering, Guilin University of Electronic Technology, Guilin 541004, P.R. China Received 24 January 2005; received in revised form 19 May 2005; accepted 2 June 2005 Available online 2 August 2005
Abstract The temperature stability of the Pr3 Pt4 compound was investigated by isothermal annealing at different temperatures, X-ray diffraction (XRD) and differential thermal analysis (DTA). It was found that the decomposition reaction Pr3 Pt4 → PrPt + PrPt2 took place at temperatures ranging approximately from 360 ◦ C to 830 ◦ C and it was an exothermal reaction. After annealing at 500–750 ◦ C for 7 days, the Pr3 Pt4 compound decomposes completely into the two neighboring compounds PrPt and PrPt2 . © 2005 Elsevier B.V. All rights reserved. Keywords: Rare earth alloys and compounds; X-ray diffraction; Phase transitions; Thermal analysis
1. Introduction
2. Experimental
According to the current version of the binary alloy phase diagrams and Pearson’s Handbook of Crystallographic Data for Intermetallic Phases [1,2], there exist seven binary compounds in the Pr–Pt binary system, namely PrPt5 (CaCu5 structure type), PrPt3 (Cu2 Mg structure type), PrPt2 (Cu2 Mg structure type), Pr3 Pt4 (Pd4 Pu3 structure type), PrPt (BFe structure type for ␣PrPt at low temperatures and CrB structure type for PrPt at high temperatures), Pr3 Pt2 (Er3 Ni2 structure type) and Pr7 Pt3 (Fe3 Th7 structure type), and the Pr3 Pt4 compound is formed in a peritectic reaction (L + PrPt Pr3 Pt4 ) at about 1620 ◦ C, which is similar to Nd3 Pt4 that is formed in a peritectic reaction (L + NdPt Nd3 Pt4 ) at 1420 ◦ C. Palenzona reported that the Pr3 Pt4 compound exists after annealing at 300 ◦ C for 5 days [3]. Our recent investigations confirmed that the Pr3 Pt4 compound exists as well after annealing at 900 ◦ C for 14 days [4]. However, it was surprising that Pr3 Pt4 does not exist in the Fe–Pt–Pr ternary alloys with more than 1 at.% Fe after annealing at 900 ◦ C for 14 days [4]. For this reason, a detailed investigation of the temperature stability of the Pr3 Pt4 compound is desirable and will be presented in this report.
The samples of the Pr3 Pt4 compound investigated were prepared by arc-melting of starting materials of at least 99.9% purity under purified argon. They were remelted four times to ensure good homogeneity. The mass losses after the melting were less than 0.5 wt.%. After arc-melting, the samples were sealed in quartz tubes pre-evacuated and refilled with some purified argon and then annealed under various conditions as listed in Table 1 and finally quenched in water. After annealing, the phase compositions of the samples were examined by powder X-ray diffraction (XRD) with Cu K␣ radiation over a 2θ angle from 20◦ to 60◦ . The differential thermal analysis (DTA) was carried out under purified nitrogen at a heating rate of 20 ◦ C/min from room temperature to 1000 ◦ C. The mass of the samples for the differential thermal analysis is 6–12 mg. The Pt/PtRh thermocouples of the DTA instrument were calibrated at the melting point of high-purity Al metal.
∗
Corresponding author. E-mail address: [email protected] (Z.F. Gu).
0925-8388/$ – see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2005.06.018
3. Results and discussion Results of X-ray diffraction measurements for the Pr3 Pt4 samples annealed at 900 ◦ C, 650 ◦ C and 300 ◦ C, respectively, are displayed in Fig. 1. The data at the top part and bottom part of Fig. 1 show that the Pr3 Pt4 annealed samples
Z.F. Gu et al. / Journal of Alloys and Compounds 407 (2006) 112–114
113
Table 1 Annealing conditions and phase compositions of Pr3 Pt4 samples Annealing conditions
Phase compositions
900 ◦ C
Annealed at for 14 days Annealed at 900 ◦ C for 14 days, then at 800 ◦ C for 7 days Annealed at 900 ◦ C for 14 days, then at 750 ◦ C for 7 days Annealed at 900 ◦ C for 14 days, then at 650 ◦ C for 7 days Annealed at 900 ◦ C for 14 days, then at 500 ◦ C for 7 days Annealed at 900 ◦ C for 14 days, then at 300 ◦ C for 7 days Annealed at 300 ◦ C for 5 days Annealed at 300 ◦ C for 5 days, then at 600 ◦ C for 1 day
and
Pr3 Pt4 + PrPt2 (small) PrPt + PrPt2 + Pr3 Pt4
and
PrPt + PrPt2
and
PrPt + PrPt2
and
PrPt + PrPt2
and
Pr3 Pt4 + PrPt2 (small)
and
Pr3 Pt4 + PrPt2 (small) PrPt + PrPt2
are approximately single phase Pr3 Pt4 except for a small amount of second phase PrPt2 and the crystal structure of the phase Pr3 Pt4 corresponds to the rhombohedral Pd4 Pu3 structure type. These results indicate clearly that the Pr3 Pt4 compound does exist at 900 ◦ C and 300 ◦ C, which is consistent with data reported in literature [3]. However, it is surprising that the Pr3 Pt4 phase does not exist in the sample annealed at 650 ◦ C for 7 days (intermediate part of Fig. 1). Only the other two phases PrPt and PrPt2 exist. Of the two phases, the former has the orthorhombic FeB structure type and the latter the cubic Cu2 Mg structure type. This suggests strongly that a decomposition reaction occurs at 650 ◦ C and the Pr3 Pt4 phase has completely transformed into the two neighboring phases PrPt and PrPt2 according to the reaction Pr3 Pt4 → PrPt + PrPt2 . Also those samples, which were annealed at 500 ◦ C, 600 ◦ C and 750 ◦ C for 7 days, respectively, consist of the two phases PrPt and PrPt2 according to the results obtained from their XRD data (see Table 1). This means that the decomposition reaction takes place as well at 500 ◦ C, 600 ◦ C and 750 ◦ C, which is totally the same as that at 650 ◦ C. However, the result of XRD obtained for the sample annealed at 800 ◦ C for 7 days reveals that it consists of the three phases Pr3 Pt4 , PrPt and PrPt2 . This implies that only
Fig. 1. XRD patterns of Pr3 Pt4 samples annealed at 900 ◦ C (top part), 650 ◦ C (intermediate part) and 300 ◦ C (bottom part), respectively.
Fig. 2. DTA curves of the Pr3 Pt4 sample annealed at 900 ◦ C, measured at a heating rate of 20 ◦ C/min, on 6 mg (top part) and 12 mg (bottom part) of powder samples, respectively.
part of Pr3 Pt4 has decomposed and transformed into PrPt and PrPt2 . From these observations mentioned above, it follows that the decomposition reaction occurs at least at 500–800 ◦ C and the reaction rate is different from temperature to temperature. The rate is slower at 800 ◦ C than at 500–750 ◦ C. All the phase compositions of the presently investigated Pr3 Pt4 samples are listed in Table 1. The differential thermal analysis curves measured on 6 mg (top part) and 12 mg (bottom part) of the Pr3 Pt4 powder samples, respectively, are displayed in Fig. 2. A large exothermic peak was observed at about 362 ◦ C at the top part of Fig. 2. It corresponds to the decomposition reaction Pr3 Pt4 → PrPt + PrPt2 . By contrast, a small endothermic peak around 830 ◦ C was observed at the bottom part of Fig. 2. This peak arises as a consequence of the composition reaction PrPt + PrPt2 → Pr3 Pt4 . Compared with the exothermic peak, the endothermic peak is much smaller, and is often too small to be observed (see top part of Fig. 2). The reason for this may be the fact that the composition reaction takes place on the boundary between the phase PrPt and PrPt2 and the course of the reaction involving atomic diffusion is impeded by the reaction product of Pr3 Pt4 . The occurrence of the composition reaction has been observed in an annealing experiment. The sample annealed at 600 ◦ C for 1 day is composed of the two phases PrPt and PrPt2 , whereas the same sample annealed at 1000 ◦ C for 10 days again is the three phases Pr3 Pt4 , PrPt and PrPt2 . These observations give further evidence that the decomposition reaction of the Pr3 Pt4 compound takes place at temperatures ranging approximately from 360 ◦ C to 830 ◦ C. Based on the experimental results of the presently investigated Pr3 Pt4 compound, we thus revise the respective part
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Z.F. Gu et al. / Journal of Alloys and Compounds 407 (2006) 112–114
4. Conclusions 1. The Pr3 Pt4 compound with the rhombohedral Pu3 Pd4 structure type is unstable and decomposes into the two neighboring compounds PrPt and PrPt2 at temperatures ranging approximately from 360 ◦ C to 830 ◦ C. 2. The decomposition reaction of the Pr3 Pt4 compound is an exothermic one with a large thermal effect and the reaction rate is faster at temperatures from 500 ◦ C to 750 ◦ C. 3. There exist two solid-state phase transformations for the Pr3 Pt4 compound upon cooling or heating, namely the eutectoid transition Pr3 Pt4 PrPt + PrPt2 at about 830 ◦ C and the peritectoid transition PrPt + PrPt2 Pr3 Pt4 at about 360 ◦ C.
Acknowledgement This work was supported by the National Natural Science Foundation of China (authorized number: 50261002). Fig. 3. Revised Pr–Pt phase diagram around the Pr3 Pt4 compound.
of the Pr–Pt phase diagram in the way shown in Fig. 3. With decreasing temperature, the Pr3 Pt4 compound is formed in a peritectic reaction (L + PrPt Pr3 Pt4 ) at about 1620 ◦ C and decomposes in a eutectoid reaction (Pr3 Pt4 PrPt + PrPt2 ) at about 830 ◦ C. When cooling to a temperature of about 360 ◦ C, the peritectoid reaction (PrPt + PrPt2 Pr3 Pt4 ) takes place and results in the combination of PrPt with PrPt2 to form Pr3 Pt4 .
References [1] T.B. Massalski (Ed.), Binary Alloy Phase Diagrams, second ed., ASM International, Materials Park, OH, 1990. [2] P. Villars, L.D. Calvert, Pearson’s Handbook of Crystallographic Data for Intermetallic Phases, ASM International, Materials Park, OH, 1991. [3] A. Palenzona, J. Less Common Met. 53 (1977) 133. [4] J. Ren, Z.F. Gu, G. Cheng, H.Y. Zhou, J. Alloys Compd. 394 (2005) 211–214.