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Crystalline arsenic trisulfide: preparation, differential scanning calorimetry and Raman scattering measurements
March 1999
Materials Letters 38 Ž1999. 336–340
Crystalline arsenic trisulfide: preparation, differential scanning calorimetry and Raman scattering measurements ˇ Zdenek ˇ Cernosek ˇ a
b
a,)
ˇ , Eva Cernoskova ˇ ´ b, Ludvık ´ Benesˇ
b
Department of General and Inorganic Chemistry, Faculty of Chemical Technology, UniÕersity of Pardubice, nam. ´ Legiı´ 565, CZ-532 10 Pardubice, Czech Republic Joint Laboratory of Solid State Chemistry of Academy of Sciences of Czech Republic and UniÕersity of Pardubice, Studentska´ 84, CZ-530 10 Pardubice, Czech Republic Received 22 May 1998; revised 1 October 1998; accepted 2 October 1998
Abstract Fully crystalline samples of high-purity arsenic trisulfide have been prepared for the first time. Comparison of X-ray diffraction spectrum ŽXRD. of prepared crystals with XRD spectrum of natural orpiment, as well as Raman scattering experiments, confirmed the crystallinity of the prepared sample. Using differential scanning calorimetry, the melting enthalpy Ž78 Jrg. and apparent activation energy of the melting process Ž306 kJrmol. were found. A kinetic analysis of the peaks, as the melting process took place, showed that melting can be described well by the Johnson–Mehl–Avrami equation with a kinetic exponent slightly more than 1. A detailed computer fit of Raman spectrum is described. q 1999 Elsevier Science B.V. All rights reserved. PACS: 81.10.Jt; 82.60.Fa; 78.30.Hv Keywords: Crystalline As 2 S 3 ; Orpiment; DSC; Raman scattering
Chalcogenide alloys based on As 2 S 3 have been studied very intensively for many years. Basic research has focused mainly on the problems of orderdisorder, intrinsic defects and photostructural changes. For more details see Refs. w1,2x and references cited therein. This area also has important technological applications—such as optical memories, and photoresists. Studies of the As–S system are complicated by the fact that the compound As 2 S 3 is an excellent glass-former and so even very slow
) Corresponding author. Tel.: q42-40-603-7158; Fax: q42-40603-7068; E-mail: [email protected]
cooling of the melt does not produce a crystal. Thus the high-purity crystalline counterpart of the glasses studied here, is not available and only natural orpiment can be used. According to our present knowledge, only preparation methods using a carbide disulfide solution under high pressure are successful w3x, but we believe that the purity of the crystals obtained is questionable. Only one quite successful synthesis of high-purity crystalline As 2 S 3 Žc-As 2 S 3 . has been reported to date by Yang et al. w4x. These authors prepared c-As 2 S 3 by the isothermal crystallization of As 2 S 3 bulk glass at 3008C for 12 days. They obtained a yellowish solid with a small fraction Žabout 1% by
00167-577Xr99r$ - see front matter q 1999 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 7 - 5 7 7 X Ž 9 8 . 0 0 1 8 5 - 2
ˇ Z. Cernosek ˇ et al.r Materials Letters 38 (1999) 336–340
volume. of glass. So, a completely crystallized sample of As 2 S 3 has not been prepared yet and natural orpiment has been used in studies, e.g., Ref. w2x. However, the purity of natural crystals, used for studies in the field of amorphous semiconductors, probably varies significantly and differs according to the place of preparation. Due to this fact, some properties reported in the literature differ, e.g., the melting point and the melting enthalpy w5,6x. It is clear that the preparation of high-purity c-As 2 S 3 is important for basic as well as for technological research. The basic idea in our preparation of c-As 2 S 3 from bulk glassy As 2 S 3 , is based on presumption that the temperature of the maximum of the nucleation rate is higher than the glass transition temperature, but lower than the melting point, because attempts to prepare c-As 2 S 3 from the melt failed. It is clear that the maximal possible temperature for isothermal annealing for crystal growth must be used after nucleation to reach the maximal growth rate. However, this temperature, which is limited by the melting of the crystal, is unknown with regard to the uncertainty of the melting point w5,6x.
337
Fig. 2. An X-ray diffraction spectrum of prepared c-As 2 S 3 and line spectrum of natural orpiment Žpowder database file no. 19– 84..
For the glass to crystal transformation, we used a computer driven high-precision annealing furnace.
Fig. 1. An optical microscope image of As 2 S 3 crystals in reflected light Ža. and the layered structure of crystal in reflected polarized light Žb..
ˇ Z. Cernosek ˇ et al.r Materials Letters 38 (1999) 336–340
338
Table 1 The characteristic parameters of the melting of synthetic crystalline As 2 S 3 and list of some published values for natural orpiment Heating rate 108Crmin
Synthetic c-As 2 S 3
Natural orpiment Ref. w5x Ref. w6x
Tm w8Cx Tons w8Cx Tp w8Cx D Hm wJrgx E) wkJrmolx E) weVx
307 323 349 78 306 3.2
307 – – 77 – –
; 315 – – 116 – –
Tm means temperature of the first departure from the baseline, E) means the apparent activation energy in the melting process. Other symbols are clear from Fig. 3.
Bulk glassy As 2 S 3 was prepared in the usual way by the direct synthesis from 5 N elements of total weight 5 g and air quenching. The coarse powder of prepared glass was sealed in an evacuated silica ampoule and placed into the furnace. Temperature was raised to 2008C with heating rate of 208Crmin. From this point, the preparation started with the temperature raising, with a heating rate 0.18Crmin up to 2958C. The sample was annealed for 7 days at this temperature. The maximum temperature devia-
tion was "0.28C. After this the sample was cooled down to 2008C with a rate of 0.18Crmin and the preparation cycle was repeated once more and finished after 7 more days. Yellow microcrystals were obtained over the whole volume of the sample. In Fig. 1, the crystals obtained are seen Ža. as well as their layered structure Žb. Žoptical microscope Olympus BX-60 was used.. An X-ray diffraction line spectrum of natural orpiment Žpowder database file no. 19–84. was used for comparison with the XRD spectrum of the prepared crystals ŽHZG 4B diffractometer, Germany, was used., as shown in Fig. 2. The newly prepared c-As 2 S 3 we used for DSC Ždifferential scanning calorimetry. and Raman scattering measurements. DSC studies ŽMettler DSC 12E calorimeter. confirmed that crystallization was completed because no glass transition was observed. Using DSC we obtained some basic data during the melting of c-As 2 S 3 , as shown in Table 1. In this table, we also list some data from Refs. w5,6x for comparison. The DSC scan Žheating rate 108Crmin., including the characteristic values of the melting process, is shown in Fig. 3. The nearly perfect correspondence of our result with data from Ref. w5x on the one hand, and differences of data from Ref. w6x on the other hand, reflects
Fig. 3. A DSC trace of melting for prepared crystalline As 2 S 3 , with a heating rate 108Crmin.
ˇ Z. Cernosek ˇ et al.r Materials Letters 38 (1999) 336–340
339
Table 2 The Raman scattering of synthetic crystalline As 2 S 3 , and a list of computer fit results for the spectrum shown in Fig. 5
Fig. 4. A Johnson–Mehl–Avrami fit Žfull lines. of DSC melting peaks Žpoints. of prepared c-As 2 S 3 . Verifying of the applicability of Johnson–Mehl–Avrami model by z Ž a . function is also shown.
probably the problem of differences in the place of occurrence of natural orpiment, as we pointed above. A kinetic analysis of melting peaks showed that the melting process can be described by Johnson–
Band position wcmy1 x
Relative integral intensity w%x
Band position wcmy1 x
Relative integral intensity w%x
63.9 71.2 84.5 107.2 137.8 146.3 156.1 163.7 180.8 188.5 204.1 209.8 219.5
0.10 0.53 0.21 0.72 2.83 0.10 4.83 2.92 1.65 1.09 3.92 0.07 0.46
294.4 309.2 312.8 327.1 354.2 357.0 361.2 370.1 384.3
10.25 4.34 12.90 0.14 18.23 13.69 15.18 0.47 5.35
Mehl–Avrami equation, see, e.g., Ref. w7x and references cited in, Fig. 4. The kinetic exponent n was found to be only a little greater than 1 Ž n ; 1.1.. It means, in our opinion, that the kinetics of the melting process of synthetic c-As 2 S 3 is close to the first order reaction mechanism, and thus probably no chemical reaction Že.g., decomposition w4x. occurs during the melting process.
Fig. 5. A Fourier transform Raman spectrum of prepared c-As 2 S 3 and a comparison with the spectrum of natural orpiment, both measured under the same experimental conditions.
340
ˇ Z. Cernosek ˇ et al.r Materials Letters 38 (1999) 336–340
Raman scattering measurements were carried out using a FT-spectrometer IFS-55 FRA 106 ŽBruker.; using the excitation line 1064 nm ŽNd:YAG laser., with a Ge-detector cooled by liquid nitrogen. A back scattering geometry was used. The Raman spectra of prepared c-As 2 S 3 and of natural orpiment are shown in Fig. 5. It can be seen that natural orpiment has slightly less resolved bands when compared to synthetic c-As 2 S 3 . A well-resolved spectrum of c-As 2 S 3 allowed us to perform a detailed computer fit of the data. The obtained band positions Ženergies. as well as relative integrated intensities of all bands are listed in Table 2. We believe that the relatively complicated process of c-As 2 S 3 preparation can be simplified when the temperature of maximum nucleation rate will be found, and the time interval for the isothermal glass to crystal transformation ought to be probably shortened, as well. We would like to note, in conclusion, that according to our experience, a homogeneous thermal field which avoids sample sublimation at isothermal annealing, as well as very good temperature control is crucial for the successful preparation of a fully crystallized sample.
Acknowledgements This work was partly supported by research grant no. 203r98r0103 of the Grant Agency of the Czech Republic. The Calorimeter Mettler DSC 12E was lent by ANATECH, Holland, and is kindly acknowledged.
References ` w1x M. Frumar, Z. Polak, ´ Z. Eernosek, ˇ B. Frumarova, ´ T. Wagner, ´ Chem. Papers 51 Ž6a. Ž1997. 310. w2x M. Frumar, A.P. Firth, A.E. Owen, J. Non-Cryst. Solids 192 and 193 Ž1995. 447. w3x S.A. Dembovskij, Yu.A. Polyakov, A.A. Vaipolin, Izv. Akad. Nauk SSSR: Neorg. Mat. 4 Ž1986. 767. w4x C.Y. Yang, M.A. Paesler, D.E. Sayers, Mat. Lett. 4 Ž1986. 233. w5x V.A. Kirmskij, A.P. Ryaposov, V.G. Yakushev, Bull. Acad. Sci. USSR: Inorg. Materials 3 Ž1967. 1931. w6x M.B. Meyers, E.J. Felty, J. Electrochem. Soc.: Solid State Science 117 Ž1970. 819. w7x J. Malek, Thermochim. Acta 267 Ž1995. 61. ´
Materials Letters 38 Ž1999. 336–340
Crystalline arsenic trisulfide: preparation, differential scanning calorimetry and Raman scattering measurements ˇ Zdenek ˇ Cernosek ˇ a
b
a,)
ˇ , Eva Cernoskova ˇ ´ b, Ludvık ´ Benesˇ
b
Department of General and Inorganic Chemistry, Faculty of Chemical Technology, UniÕersity of Pardubice, nam. ´ Legiı´ 565, CZ-532 10 Pardubice, Czech Republic Joint Laboratory of Solid State Chemistry of Academy of Sciences of Czech Republic and UniÕersity of Pardubice, Studentska´ 84, CZ-530 10 Pardubice, Czech Republic Received 22 May 1998; revised 1 October 1998; accepted 2 October 1998
Abstract Fully crystalline samples of high-purity arsenic trisulfide have been prepared for the first time. Comparison of X-ray diffraction spectrum ŽXRD. of prepared crystals with XRD spectrum of natural orpiment, as well as Raman scattering experiments, confirmed the crystallinity of the prepared sample. Using differential scanning calorimetry, the melting enthalpy Ž78 Jrg. and apparent activation energy of the melting process Ž306 kJrmol. were found. A kinetic analysis of the peaks, as the melting process took place, showed that melting can be described well by the Johnson–Mehl–Avrami equation with a kinetic exponent slightly more than 1. A detailed computer fit of Raman spectrum is described. q 1999 Elsevier Science B.V. All rights reserved. PACS: 81.10.Jt; 82.60.Fa; 78.30.Hv Keywords: Crystalline As 2 S 3 ; Orpiment; DSC; Raman scattering
Chalcogenide alloys based on As 2 S 3 have been studied very intensively for many years. Basic research has focused mainly on the problems of orderdisorder, intrinsic defects and photostructural changes. For more details see Refs. w1,2x and references cited therein. This area also has important technological applications—such as optical memories, and photoresists. Studies of the As–S system are complicated by the fact that the compound As 2 S 3 is an excellent glass-former and so even very slow
) Corresponding author. Tel.: q42-40-603-7158; Fax: q42-40603-7068; E-mail: [email protected]
cooling of the melt does not produce a crystal. Thus the high-purity crystalline counterpart of the glasses studied here, is not available and only natural orpiment can be used. According to our present knowledge, only preparation methods using a carbide disulfide solution under high pressure are successful w3x, but we believe that the purity of the crystals obtained is questionable. Only one quite successful synthesis of high-purity crystalline As 2 S 3 Žc-As 2 S 3 . has been reported to date by Yang et al. w4x. These authors prepared c-As 2 S 3 by the isothermal crystallization of As 2 S 3 bulk glass at 3008C for 12 days. They obtained a yellowish solid with a small fraction Žabout 1% by
00167-577Xr99r$ - see front matter q 1999 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 7 - 5 7 7 X Ž 9 8 . 0 0 1 8 5 - 2
ˇ Z. Cernosek ˇ et al.r Materials Letters 38 (1999) 336–340
volume. of glass. So, a completely crystallized sample of As 2 S 3 has not been prepared yet and natural orpiment has been used in studies, e.g., Ref. w2x. However, the purity of natural crystals, used for studies in the field of amorphous semiconductors, probably varies significantly and differs according to the place of preparation. Due to this fact, some properties reported in the literature differ, e.g., the melting point and the melting enthalpy w5,6x. It is clear that the preparation of high-purity c-As 2 S 3 is important for basic as well as for technological research. The basic idea in our preparation of c-As 2 S 3 from bulk glassy As 2 S 3 , is based on presumption that the temperature of the maximum of the nucleation rate is higher than the glass transition temperature, but lower than the melting point, because attempts to prepare c-As 2 S 3 from the melt failed. It is clear that the maximal possible temperature for isothermal annealing for crystal growth must be used after nucleation to reach the maximal growth rate. However, this temperature, which is limited by the melting of the crystal, is unknown with regard to the uncertainty of the melting point w5,6x.
337
Fig. 2. An X-ray diffraction spectrum of prepared c-As 2 S 3 and line spectrum of natural orpiment Žpowder database file no. 19– 84..
For the glass to crystal transformation, we used a computer driven high-precision annealing furnace.
Fig. 1. An optical microscope image of As 2 S 3 crystals in reflected light Ža. and the layered structure of crystal in reflected polarized light Žb..
ˇ Z. Cernosek ˇ et al.r Materials Letters 38 (1999) 336–340
338
Table 1 The characteristic parameters of the melting of synthetic crystalline As 2 S 3 and list of some published values for natural orpiment Heating rate 108Crmin
Synthetic c-As 2 S 3
Natural orpiment Ref. w5x Ref. w6x
Tm w8Cx Tons w8Cx Tp w8Cx D Hm wJrgx E) wkJrmolx E) weVx
307 323 349 78 306 3.2
307 – – 77 – –
; 315 – – 116 – –
Tm means temperature of the first departure from the baseline, E) means the apparent activation energy in the melting process. Other symbols are clear from Fig. 3.
Bulk glassy As 2 S 3 was prepared in the usual way by the direct synthesis from 5 N elements of total weight 5 g and air quenching. The coarse powder of prepared glass was sealed in an evacuated silica ampoule and placed into the furnace. Temperature was raised to 2008C with heating rate of 208Crmin. From this point, the preparation started with the temperature raising, with a heating rate 0.18Crmin up to 2958C. The sample was annealed for 7 days at this temperature. The maximum temperature devia-
tion was "0.28C. After this the sample was cooled down to 2008C with a rate of 0.18Crmin and the preparation cycle was repeated once more and finished after 7 more days. Yellow microcrystals were obtained over the whole volume of the sample. In Fig. 1, the crystals obtained are seen Ža. as well as their layered structure Žb. Žoptical microscope Olympus BX-60 was used.. An X-ray diffraction line spectrum of natural orpiment Žpowder database file no. 19–84. was used for comparison with the XRD spectrum of the prepared crystals ŽHZG 4B diffractometer, Germany, was used., as shown in Fig. 2. The newly prepared c-As 2 S 3 we used for DSC Ždifferential scanning calorimetry. and Raman scattering measurements. DSC studies ŽMettler DSC 12E calorimeter. confirmed that crystallization was completed because no glass transition was observed. Using DSC we obtained some basic data during the melting of c-As 2 S 3 , as shown in Table 1. In this table, we also list some data from Refs. w5,6x for comparison. The DSC scan Žheating rate 108Crmin., including the characteristic values of the melting process, is shown in Fig. 3. The nearly perfect correspondence of our result with data from Ref. w5x on the one hand, and differences of data from Ref. w6x on the other hand, reflects
Fig. 3. A DSC trace of melting for prepared crystalline As 2 S 3 , with a heating rate 108Crmin.
ˇ Z. Cernosek ˇ et al.r Materials Letters 38 (1999) 336–340
339
Table 2 The Raman scattering of synthetic crystalline As 2 S 3 , and a list of computer fit results for the spectrum shown in Fig. 5
Fig. 4. A Johnson–Mehl–Avrami fit Žfull lines. of DSC melting peaks Žpoints. of prepared c-As 2 S 3 . Verifying of the applicability of Johnson–Mehl–Avrami model by z Ž a . function is also shown.
probably the problem of differences in the place of occurrence of natural orpiment, as we pointed above. A kinetic analysis of melting peaks showed that the melting process can be described by Johnson–
Band position wcmy1 x
Relative integral intensity w%x
Band position wcmy1 x
Relative integral intensity w%x
63.9 71.2 84.5 107.2 137.8 146.3 156.1 163.7 180.8 188.5 204.1 209.8 219.5
0.10 0.53 0.21 0.72 2.83 0.10 4.83 2.92 1.65 1.09 3.92 0.07 0.46
294.4 309.2 312.8 327.1 354.2 357.0 361.2 370.1 384.3
10.25 4.34 12.90 0.14 18.23 13.69 15.18 0.47 5.35
Mehl–Avrami equation, see, e.g., Ref. w7x and references cited in, Fig. 4. The kinetic exponent n was found to be only a little greater than 1 Ž n ; 1.1.. It means, in our opinion, that the kinetics of the melting process of synthetic c-As 2 S 3 is close to the first order reaction mechanism, and thus probably no chemical reaction Že.g., decomposition w4x. occurs during the melting process.
Fig. 5. A Fourier transform Raman spectrum of prepared c-As 2 S 3 and a comparison with the spectrum of natural orpiment, both measured under the same experimental conditions.
340
ˇ Z. Cernosek ˇ et al.r Materials Letters 38 (1999) 336–340
Raman scattering measurements were carried out using a FT-spectrometer IFS-55 FRA 106 ŽBruker.; using the excitation line 1064 nm ŽNd:YAG laser., with a Ge-detector cooled by liquid nitrogen. A back scattering geometry was used. The Raman spectra of prepared c-As 2 S 3 and of natural orpiment are shown in Fig. 5. It can be seen that natural orpiment has slightly less resolved bands when compared to synthetic c-As 2 S 3 . A well-resolved spectrum of c-As 2 S 3 allowed us to perform a detailed computer fit of the data. The obtained band positions Ženergies. as well as relative integrated intensities of all bands are listed in Table 2. We believe that the relatively complicated process of c-As 2 S 3 preparation can be simplified when the temperature of maximum nucleation rate will be found, and the time interval for the isothermal glass to crystal transformation ought to be probably shortened, as well. We would like to note, in conclusion, that according to our experience, a homogeneous thermal field which avoids sample sublimation at isothermal annealing, as well as very good temperature control is crucial for the successful preparation of a fully crystallized sample.
Acknowledgements This work was partly supported by research grant no. 203r98r0103 of the Grant Agency of the Czech Republic. The Calorimeter Mettler DSC 12E was lent by ANATECH, Holland, and is kindly acknowledged.
References ` w1x M. Frumar, Z. Polak, ´ Z. Eernosek, ˇ B. Frumarova, ´ T. Wagner, ´ Chem. Papers 51 Ž6a. Ž1997. 310. w2x M. Frumar, A.P. Firth, A.E. Owen, J. Non-Cryst. Solids 192 and 193 Ž1995. 447. w3x S.A. Dembovskij, Yu.A. Polyakov, A.A. Vaipolin, Izv. Akad. Nauk SSSR: Neorg. Mat. 4 Ž1986. 767. w4x C.Y. Yang, M.A. Paesler, D.E. Sayers, Mat. Lett. 4 Ž1986. 233. w5x V.A. Kirmskij, A.P. Ryaposov, V.G. Yakushev, Bull. Acad. Sci. USSR: Inorg. Materials 3 Ž1967. 1931. w6x M.B. Meyers, E.J. Felty, J. Electrochem. Soc.: Solid State Science 117 Ž1970. 819. w7x J. Malek, Thermochim. Acta 267 Ž1995. 61. ´