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Phase formation in films of the As2Se3Yb system
Thin Solid Films, 237 (1994) 213-216
213
Phase formation in films of the As2Se3-Yb system E. G . E f e n d i y e v , E. Sh. H a j i y e v , R . B. S h a f i z a d e a n d T . M . I l y a s o v Institute of Physics, Academy of Sciences of Azerbaijan Republic, 33 Azizbekov Prospect, Baku (Azerbaijan)
(Received June 3, 1992; revised November 3, 1992; accepted March 10, 1993)
Abstract Films on the condensation plane were obtained by evaporation of glassy As2Se3 and polycrystalline Yb from two furnaces 10 cm apart. The phase formation before and after annealing was investigated by high energy electron diffraction. Films of YbAs2Se4, YbAsaSe 7 and YbAsSe 3 have been obtained. Their crystallographic data and the obtaining regimes of each mentioned phase were established. It was discovered that the obtained phases are formed in the film state at much lower temperatures than those in the bulk samples.
1. Introduction The chalocogenide materials containing f elements with magnetic properties have been studied very little [1-6]. The amorphous materials containing f elements represent a new class of amorphous materials that have been investigated slightly more often [7]. These kinds of material may be applied in devices which are controlled by external magnetic fields [3]. There are data confirming the possibility of utilization of these materials in acousto-optics [8]. Glassy semiconductors of the L a A s - S ( L a - S m , Yb) systems are characterized by a high coefficient of acousto-optic quality and are transparent in the IR at 2 = 0.6-12 gm. These semiconductors are recommended for utilization in systems of optical processing of information for control of emission from a helium-neon laser [9]. Some glasses based on As2Se3, which contain Ga and Yb, have much higher photoconductivity than the pure compounds and they can be used as photoconductivity layers in a transmission television tube of the Vidicon type and also as photoresistive materials [10]. These materials have not been investigated in the film state. Phase formation has been studied in some similar systems in bulk specimens [1-6]. For instance, the As2Se3-Yb system phase diagram has been obtained by physicochemical analysis and the compounds formed in bulk specimens have been established [4]. Alloy synthesis was carried out by straightforward melting of the elements in quartz ampoules pumped out to 10 -1 Pa in the temperature range 1123-1473 K with periodic mixing in the liquid state. The research was carried out by using differential thermal analysis, X-ray phase analysis and measurements of micro-
0040-6090/94/$7.00
hardness. A glass formation region extending to 10 mol.% YbSe was detected in the As2Se3-Yb system [4]. The compounds YbAsaSeT, YbAs2Se 4 and Yb3As4Se 9 are formed at 998 K, 1003 K and 1153 K respectively. The YbAs2Se4 compound melts incongruently [4]. The phase diagrams for YbAs4SeT, YbAs2Se 4 and Yb3AsaSe9 are also presented. It is also shown that the compounds YbAsaSe 7 and YbAs2Se4 are crystallized in the rhombic system with the lattice parameters a = 6 . 8 5 A , b = 2 3 . 5 2 A , and c = 4 . 0 6 ~ , and a = 11.34 A,, b = 13.04 A_ and c = 3.98 A. respectively [4]. The AsaSe3-YbzSe 3 system was studied by physicochemical analysis methods and the phase diagram was plotted in ref. 5. It was established that the region of glass formation extends to 8 mol.% ASRSe3. The existence of the YbAsSe3 phase was found in the As2Se 3Yb2Se 3 system. YbAsSe3 has a melting temperature of 1020K. No other compounds were obtained in this system [5]. The AsSe-YbSe, AsSe-YbAs4Se7 and AsSeYb3As4Se 9 systems were studied by physicochemical analysis methods and it was established that these sections are quasi-binary sections of the Y b - A s - S e ternary system [6]. The region of glass formation was discovered in all the tested systems. Thus it is concluded that the YbAs4SeT, YbAs2Se4, Yb3As4Se9 and YbAsSe3 ternary compounds exist in bulk samples of the Y b - A s - S e system. However, no data on phase formation in films of the Y b - A s - S e system and of its quasi-binary section are given in the literature. Therefore the task of the present work is to study phase formation in films of the As2Se3-Yb system.
© 1994-- Elsevier Sequoia. All rights reserved
E. G. Efi,nd(vev et al./ Phase /brmation in films o f A.ssSe 3 Yb system
214
2. Experimental details Thin films of Yb and As:Se3 were obtained by vacuum evaporation. The films of Yb are polycrystalline (Fig. l(a)) and the films of As:Se3 amorphous (Fig. l(b)). Then the AszSe3 films are crystallized on amorphous substrates such as celluloid films at T = 473 K (Fig. l(c)) in the monoclinic space group P2j/c (C25h), with the parameters a = 12.053/~, b = 9 . 8 9 ~ , c = 4.277 ,~ and fi = 90 ° 28' [ 11]. Films were obtained on the condensation plane by the evaporation of the polycrystalline Yb from a " b o a t " furnace made of tungsten alloy and the amorphous AseSe3 from a "basket" furnace having a conical form. The evaporation temperatures of Yb and AszSe 3 were measured with a platinum (platinum-rhodium) thermocouple and were 1123 K and 573 K respectively.
We used crystalline NaCl as the substrate. The substrate temperature was similar to room temperature. The distance from the furnace to the substrates was 6cm. The length L of the condensation plane was 10cm. The experimental vacuum level was about 10 3 Pa. First, the As2Se3 and Yb were simultaneously evaporated by the Vekshinsky [12] method under the above-mentioned conditions. The calculated thickness of the Yb in the furnace was 150~, and that of the As2Se3 in its furnace was 200,~. Then As2Se3 and Yb were simultaneously evaporated under the same conditions.
Z2Z
022
2~q
Oqq
(a)
(a)
512
23q
z31
501
~15
54~
(b) (b) ~55
11.5 232 520
121 011
442
111
13#
2.21
2ga
202
222
042
(c) Fig. 1. Electron diffraction patterns of (a) a polycrystalline Yb film, (b) an amorphous As2Se3 fihn and (c) a polycrystalline AszSe3 film.
402
450
5ffi
420
320
150
44{3
]12.
4~2
~2
(c) Fig. 2. Electron difraction patterns of (a) an As2Se 3 ÷ Yb double film, (b) a polycrystalline YbAs4Se 7 film and (c) a polycrystalline YbAs2Se4 film.
E. G. Efendiyev et al./ Phase formation in films of As2Se 3 Yb system
The structures of the examined films before and after the anneal were studied by the high energy electron diffraction method using E G and EMR-102 electron microscopes. The existence of the ternary compounds was determined by calculation using the electron diffraction patterns in Figs. 2(b) and 2(c).
3. Results and discussion
The electron diffraction analysis of films formed on the condensation plane showed that no chemical interaction between the polycrystalline Yb and amorphous As2Se3 took place (Fig. 2(a)). Thermal annealing of the films at T = 373 K causes a significant change in the structures of the samples. Electron diffraction pattern analysis shows that the rhombic modification of the YbAs4Se7 phase with the parameters a = 6.85/~, b = 23.52/~ and c = 4.06/~ [4] is formed directly in the furnace with Yb, i.e. at L = 0 (Fig. 2(b)). However, at L = 2.5 cm this phase is not observed. The formation region of the YbAs4Se 7 phase was extended to L = 4 cm for an annealing temperature T of 423 K. The YbAs2Se4 phase of the rhombic system with the lattice parameters a = 11.3/~, b = 13.0/~ and c = 3.98 A [4] was formed at T = 473 K. The electron diffraction pattern of this phase is given in Fig. 2(c). However, this phase exists in a very narrow range L = 4 - 4 . 5 cm. Thermal annealing at T = 573 K leads to the formation of the YbAsSe3 tetragonal phase with the lattice parameters a = b = 12.55/~ and c = 8.83/~ [5]. This phase is observed up to L = 4 cm. The YbAs4Se 7 phase observed earlier is formed in the L = 7 - 8 cm region. In the rest of the regions, the electron diffraction pattern obtained from thermally annealed films at T = 573 K shows no diffraction lines present other than those of the Yb and AszSe 3. This distribution of phases in the condensation plane at T = 573 K m a y be explained by partial re-evaporation of light volatile components. In the films of the As2Se3-Yb system, the YbAs4Se7, YbAs2Se4 and YbAsSe3 phases are observed in the temperature range 373-573 K. It should be noted that the above-discussed phases are formed in the film state at a much lower temperature than those in the bulk samples. In particular, in the bulk samples of the AszSe3-YbSe system, the YbAs4Se7 phase is formed at T = 998 K [4], whereas in the film state it is formed at T = 373 K. However, it is necessary to note that this phase is obtained from As2Se3 and YbSe in ref. 4, but in our experiment from As2Se3 and ytterbium. According to ref. 4, the YbAs2Se4 phase is formed in bulk samples at T = 1003 K, while in the film state it is formed at T = 473 K.
215
The formation of the YbAsSe3 tetragonal modification occurs in bulk samples at T = 1023 K [5], while in the film state it occurs at T = 573 K. However, it should be noted that the YbAsSe3 phase is formed from As2Se3 and Yb2Se3 in ref. 5, while in our work the same phase is formed from As2Se3 and crystalline ytterbium in the film state. Simultaneous evaporation of As2Se3 and ytterbium did not give new results in the phase formation study of the As2Se3 Yb system. According to ref. 12, the function of material distribution at each point of the condensation plane is calculated from the formula Q
1
q = 4rth 2 (1 + :~2)3/2
(1)
where q is the function of material distribution at the condensation plane, Q is the amount of evaporated material, h is the distance of the furnace from the condensation plane and 7 = L / h , where L is defined above. According to ref. 12, if we take into account eqn. (1) the composition of the mixture, co0densed at point L, can be unambiguously defined by the percentage content of the components in the mixture PYb --
qVb 100% qVb q'- qAs2Se3
PAs2 Se3 --
(2)
q A s 2 S e 3 1000/0 qYb + qAszSe3
However, we showed that the calculated Pvb and PAs2S~3 did not agree with the experimental values. Thus, for instance, from eqn. (2) the composition YbAsaSe 7 would be expected to appear in the region L = 4.0 4.5 cm, but we found it to be at L = 0.0 cm, just in the furnace for Yb. These are due to migration processes, which take place during the vacuum deposition of components on the surface of the condensation plane. These processes are exhibited more distinctly when the films are subjected to heat treatment on the condensation plane. Reactive diffusion takes place in these processes and new phases are formed as a result. We observed these phases in our experiments (Figs. 2(b) and 2(c)). The above-mentioned processes result in the fact that the real distribution of phases differs from the distribution that we calculated. These processes are exhibited not only when the YbAs4Se7 forms, but also for YbAszSe4 and YbAsSe3.
References 1 R . Ceolin and P. Khodadad, Ct. R. Acad. Sci. Par~,Ser C, 272 (1971) 1769. 2 S. Barnier, M. Guittard and J. Flahaut, Mater. Res. BuH., 14 (1979) 973.
216
E. G. Efendiyev et al. / Phase Jormation in films of As2Se 3- Yb system
3 P. G. Rustamov, O. M. Aliyev and T. Ch. Kurbanov, Troynye Khalkogenidy Redkozemelnykh Elementov, Elm, Baku, 1981. 4 P. G. Rustamov and T. M. Ilyasov, Zh. Neorg. Khim., 29 (1984) 2975. 5 P. G. Rustamov, T. M. Ilyasov and L. A. Mamedova, Zh. Neorg. Khim., 30 (1985) 2987. 6 P. G. Rustamov, T. M. llyasov and L. A. Mamedova, Zh. Neorg. Khim., 31 (1986) 2437. 7 I. V. Zolotukhin, Fizicheskie Svoystva Amorfnykh Metallicheskikh Materialov, Metallurgiya, Moscow, 1986.
8 V. I. Balakshy, V. I. Parigin and L. E. Chirkov, Fizicheskie Osnovy Akustooptiki, Radio i Svyaz, Moscow, 1985.
9 USSR Pat. 1374695. 10 USSR Pat. 96,761; USSR Pat. 265165. 11 N+ Ch. Abricosov, V. F. Bankina, I. V. Porechkaya, E. V. Skudnova and S. N. Chizhevskaya, Polyprovodnikovye Khalkogenidi i Splavy na ikh Osnove, Nauka, Moscow, 1975. 12 S. A. Vekshinsky, Nov)' Metod Metallograficheskogo lssledovaniya Splavov, Gosudarstvennoe lzdatelstvo Tekhnikoteoretichekoy Literatury, Moscow, 1944.
213
Phase formation in films of the As2Se3-Yb system E. G . E f e n d i y e v , E. Sh. H a j i y e v , R . B. S h a f i z a d e a n d T . M . I l y a s o v Institute of Physics, Academy of Sciences of Azerbaijan Republic, 33 Azizbekov Prospect, Baku (Azerbaijan)
(Received June 3, 1992; revised November 3, 1992; accepted March 10, 1993)
Abstract Films on the condensation plane were obtained by evaporation of glassy As2Se3 and polycrystalline Yb from two furnaces 10 cm apart. The phase formation before and after annealing was investigated by high energy electron diffraction. Films of YbAs2Se4, YbAsaSe 7 and YbAsSe 3 have been obtained. Their crystallographic data and the obtaining regimes of each mentioned phase were established. It was discovered that the obtained phases are formed in the film state at much lower temperatures than those in the bulk samples.
1. Introduction The chalocogenide materials containing f elements with magnetic properties have been studied very little [1-6]. The amorphous materials containing f elements represent a new class of amorphous materials that have been investigated slightly more often [7]. These kinds of material may be applied in devices which are controlled by external magnetic fields [3]. There are data confirming the possibility of utilization of these materials in acousto-optics [8]. Glassy semiconductors of the L a A s - S ( L a - S m , Yb) systems are characterized by a high coefficient of acousto-optic quality and are transparent in the IR at 2 = 0.6-12 gm. These semiconductors are recommended for utilization in systems of optical processing of information for control of emission from a helium-neon laser [9]. Some glasses based on As2Se3, which contain Ga and Yb, have much higher photoconductivity than the pure compounds and they can be used as photoconductivity layers in a transmission television tube of the Vidicon type and also as photoresistive materials [10]. These materials have not been investigated in the film state. Phase formation has been studied in some similar systems in bulk specimens [1-6]. For instance, the As2Se3-Yb system phase diagram has been obtained by physicochemical analysis and the compounds formed in bulk specimens have been established [4]. Alloy synthesis was carried out by straightforward melting of the elements in quartz ampoules pumped out to 10 -1 Pa in the temperature range 1123-1473 K with periodic mixing in the liquid state. The research was carried out by using differential thermal analysis, X-ray phase analysis and measurements of micro-
0040-6090/94/$7.00
hardness. A glass formation region extending to 10 mol.% YbSe was detected in the As2Se3-Yb system [4]. The compounds YbAsaSeT, YbAs2Se 4 and Yb3As4Se 9 are formed at 998 K, 1003 K and 1153 K respectively. The YbAs2Se4 compound melts incongruently [4]. The phase diagrams for YbAs4SeT, YbAs2Se 4 and Yb3AsaSe9 are also presented. It is also shown that the compounds YbAsaSe 7 and YbAs2Se4 are crystallized in the rhombic system with the lattice parameters a = 6 . 8 5 A , b = 2 3 . 5 2 A , and c = 4 . 0 6 ~ , and a = 11.34 A,, b = 13.04 A_ and c = 3.98 A. respectively [4]. The AsaSe3-YbzSe 3 system was studied by physicochemical analysis methods and the phase diagram was plotted in ref. 5. It was established that the region of glass formation extends to 8 mol.% ASRSe3. The existence of the YbAsSe3 phase was found in the As2Se 3Yb2Se 3 system. YbAsSe3 has a melting temperature of 1020K. No other compounds were obtained in this system [5]. The AsSe-YbSe, AsSe-YbAs4Se7 and AsSeYb3As4Se 9 systems were studied by physicochemical analysis methods and it was established that these sections are quasi-binary sections of the Y b - A s - S e ternary system [6]. The region of glass formation was discovered in all the tested systems. Thus it is concluded that the YbAs4SeT, YbAs2Se4, Yb3As4Se9 and YbAsSe3 ternary compounds exist in bulk samples of the Y b - A s - S e system. However, no data on phase formation in films of the Y b - A s - S e system and of its quasi-binary section are given in the literature. Therefore the task of the present work is to study phase formation in films of the As2Se3-Yb system.
© 1994-- Elsevier Sequoia. All rights reserved
E. G. Efi,nd(vev et al./ Phase /brmation in films o f A.ssSe 3 Yb system
214
2. Experimental details Thin films of Yb and As:Se3 were obtained by vacuum evaporation. The films of Yb are polycrystalline (Fig. l(a)) and the films of As:Se3 amorphous (Fig. l(b)). Then the AszSe3 films are crystallized on amorphous substrates such as celluloid films at T = 473 K (Fig. l(c)) in the monoclinic space group P2j/c (C25h), with the parameters a = 12.053/~, b = 9 . 8 9 ~ , c = 4.277 ,~ and fi = 90 ° 28' [ 11]. Films were obtained on the condensation plane by the evaporation of the polycrystalline Yb from a " b o a t " furnace made of tungsten alloy and the amorphous AseSe3 from a "basket" furnace having a conical form. The evaporation temperatures of Yb and AszSe 3 were measured with a platinum (platinum-rhodium) thermocouple and were 1123 K and 573 K respectively.
We used crystalline NaCl as the substrate. The substrate temperature was similar to room temperature. The distance from the furnace to the substrates was 6cm. The length L of the condensation plane was 10cm. The experimental vacuum level was about 10 3 Pa. First, the As2Se3 and Yb were simultaneously evaporated by the Vekshinsky [12] method under the above-mentioned conditions. The calculated thickness of the Yb in the furnace was 150~, and that of the As2Se3 in its furnace was 200,~. Then As2Se3 and Yb were simultaneously evaporated under the same conditions.
Z2Z
022
2~q
Oqq
(a)
(a)
512
23q
z31
501
~15
54~
(b) (b) ~55
11.5 232 520
121 011
442
111
13#
2.21
2ga
202
222
042
(c) Fig. 1. Electron diffraction patterns of (a) a polycrystalline Yb film, (b) an amorphous As2Se3 fihn and (c) a polycrystalline AszSe3 film.
402
450
5ffi
420
320
150
44{3
]12.
4~2
~2
(c) Fig. 2. Electron difraction patterns of (a) an As2Se 3 ÷ Yb double film, (b) a polycrystalline YbAs4Se 7 film and (c) a polycrystalline YbAs2Se4 film.
E. G. Efendiyev et al./ Phase formation in films of As2Se 3 Yb system
The structures of the examined films before and after the anneal were studied by the high energy electron diffraction method using E G and EMR-102 electron microscopes. The existence of the ternary compounds was determined by calculation using the electron diffraction patterns in Figs. 2(b) and 2(c).
3. Results and discussion
The electron diffraction analysis of films formed on the condensation plane showed that no chemical interaction between the polycrystalline Yb and amorphous As2Se3 took place (Fig. 2(a)). Thermal annealing of the films at T = 373 K causes a significant change in the structures of the samples. Electron diffraction pattern analysis shows that the rhombic modification of the YbAs4Se7 phase with the parameters a = 6.85/~, b = 23.52/~ and c = 4.06/~ [4] is formed directly in the furnace with Yb, i.e. at L = 0 (Fig. 2(b)). However, at L = 2.5 cm this phase is not observed. The formation region of the YbAs4Se 7 phase was extended to L = 4 cm for an annealing temperature T of 423 K. The YbAs2Se4 phase of the rhombic system with the lattice parameters a = 11.3/~, b = 13.0/~ and c = 3.98 A [4] was formed at T = 473 K. The electron diffraction pattern of this phase is given in Fig. 2(c). However, this phase exists in a very narrow range L = 4 - 4 . 5 cm. Thermal annealing at T = 573 K leads to the formation of the YbAsSe3 tetragonal phase with the lattice parameters a = b = 12.55/~ and c = 8.83/~ [5]. This phase is observed up to L = 4 cm. The YbAs4Se 7 phase observed earlier is formed in the L = 7 - 8 cm region. In the rest of the regions, the electron diffraction pattern obtained from thermally annealed films at T = 573 K shows no diffraction lines present other than those of the Yb and AszSe 3. This distribution of phases in the condensation plane at T = 573 K m a y be explained by partial re-evaporation of light volatile components. In the films of the As2Se3-Yb system, the YbAs4Se7, YbAs2Se4 and YbAsSe3 phases are observed in the temperature range 373-573 K. It should be noted that the above-discussed phases are formed in the film state at a much lower temperature than those in the bulk samples. In particular, in the bulk samples of the AszSe3-YbSe system, the YbAs4Se7 phase is formed at T = 998 K [4], whereas in the film state it is formed at T = 373 K. However, it is necessary to note that this phase is obtained from As2Se3 and YbSe in ref. 4, but in our experiment from As2Se3 and ytterbium. According to ref. 4, the YbAs2Se4 phase is formed in bulk samples at T = 1003 K, while in the film state it is formed at T = 473 K.
215
The formation of the YbAsSe3 tetragonal modification occurs in bulk samples at T = 1023 K [5], while in the film state it occurs at T = 573 K. However, it should be noted that the YbAsSe3 phase is formed from As2Se3 and Yb2Se3 in ref. 5, while in our work the same phase is formed from As2Se3 and crystalline ytterbium in the film state. Simultaneous evaporation of As2Se3 and ytterbium did not give new results in the phase formation study of the As2Se3 Yb system. According to ref. 12, the function of material distribution at each point of the condensation plane is calculated from the formula Q
1
q = 4rth 2 (1 + :~2)3/2
(1)
where q is the function of material distribution at the condensation plane, Q is the amount of evaporated material, h is the distance of the furnace from the condensation plane and 7 = L / h , where L is defined above. According to ref. 12, if we take into account eqn. (1) the composition of the mixture, co0densed at point L, can be unambiguously defined by the percentage content of the components in the mixture PYb --
qVb 100% qVb q'- qAs2Se3
PAs2 Se3 --
(2)
q A s 2 S e 3 1000/0 qYb + qAszSe3
However, we showed that the calculated Pvb and PAs2S~3 did not agree with the experimental values. Thus, for instance, from eqn. (2) the composition YbAsaSe 7 would be expected to appear in the region L = 4.0 4.5 cm, but we found it to be at L = 0.0 cm, just in the furnace for Yb. These are due to migration processes, which take place during the vacuum deposition of components on the surface of the condensation plane. These processes are exhibited more distinctly when the films are subjected to heat treatment on the condensation plane. Reactive diffusion takes place in these processes and new phases are formed as a result. We observed these phases in our experiments (Figs. 2(b) and 2(c)). The above-mentioned processes result in the fact that the real distribution of phases differs from the distribution that we calculated. These processes are exhibited not only when the YbAs4Se7 forms, but also for YbAszSe4 and YbAsSe3.
References 1 R . Ceolin and P. Khodadad, Ct. R. Acad. Sci. Par~,Ser C, 272 (1971) 1769. 2 S. Barnier, M. Guittard and J. Flahaut, Mater. Res. BuH., 14 (1979) 973.
216
E. G. Efendiyev et al. / Phase Jormation in films of As2Se 3- Yb system
3 P. G. Rustamov, O. M. Aliyev and T. Ch. Kurbanov, Troynye Khalkogenidy Redkozemelnykh Elementov, Elm, Baku, 1981. 4 P. G. Rustamov and T. M. Ilyasov, Zh. Neorg. Khim., 29 (1984) 2975. 5 P. G. Rustamov, T. M. Ilyasov and L. A. Mamedova, Zh. Neorg. Khim., 30 (1985) 2987. 6 P. G. Rustamov, T. M. llyasov and L. A. Mamedova, Zh. Neorg. Khim., 31 (1986) 2437. 7 I. V. Zolotukhin, Fizicheskie Svoystva Amorfnykh Metallicheskikh Materialov, Metallurgiya, Moscow, 1986.
8 V. I. Balakshy, V. I. Parigin and L. E. Chirkov, Fizicheskie Osnovy Akustooptiki, Radio i Svyaz, Moscow, 1985.
9 USSR Pat. 1374695. 10 USSR Pat. 96,761; USSR Pat. 265165. 11 N+ Ch. Abricosov, V. F. Bankina, I. V. Porechkaya, E. V. Skudnova and S. N. Chizhevskaya, Polyprovodnikovye Khalkogenidi i Splavy na ikh Osnove, Nauka, Moscow, 1975. 12 S. A. Vekshinsky, Nov)' Metod Metallograficheskogo lssledovaniya Splavov, Gosudarstvennoe lzdatelstvo Tekhnikoteoretichekoy Literatury, Moscow, 1944.