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High-pressure synthesis of a new copper thioborate, CuBS2
Materials Letters 61 (2007) 2382 – 2384 www.elsevier.com/locate/matlet
High-pressure synthesis of a new copper thioborate, CuBS2 Takahiro Kajiki, Yamato Hayashi, Hirotsugu Takizawa ⁎ Department of Applied Chemistry, Graduate School of Engineering, Tohoku University, Aoba-yama 07, Sendai 980-8579, Japan Received 2 June 2006; accepted 7 September 2006 Available online 26 September 2006
Abstract A new copper thioborate, CuBS2, was synthesized at high-pressure/temperature condition of 3 GPa and 700–900 °C. The crystal structure was refined by the Rietveld analysis of the powder X-ray diffraction data. The compound crystallizes into a tetragonal unit cell (a = 0.5044(1) nm, c = 0.8947(2) nm, space group: I-42d), isostructural with CuMS2 chalcopyrite compounds (M: Al, Ga, and In). The compound is the first representative of the chalcopyrite-type family consisting of BS4-tetrahedra. From the UV–Vis diffuse reflectance spectrum, the optical band gap of CuBS2 was estimated to be Eg = 3.61 eV. © 2006 Elsevier B.V. All rights reserved. Keywords: Crystal structure; Intermetallic alloys and compounds; High-pressure synthesis; Rietveld analysis; Chalcopyrite
1. Introduction
2. Experimental
Recently, a number of ternary thioborates (MxBySz: metal borosulfides) have been synthesized. Among these thioborates, compounds containing lithium have been extensively investigated for the specific application to super ionic conducting materials [1,2]. Some of these crystalline thioborates consist of characteristic “macro-tetrahedral” structural units represented by formulas of [B4S10]8− or [B10S18]6−. These macro-tetrahedra have shapes of large pyramidal structures built up from covalent BS4-tetrahedra. We have previously examined the high-pressure synthesis of binary B–S and ternary thioborate systems and successfully synthesized some new high-pressure phases, BS [3], B2S3 [4], and CaB2S4 [5]. The results suggest that the formation of BS4tetrahedra (tetrahedral boron atom) is favored under high-pressure condition. The binary compound, B2S3, is built up from two kinds of electrically neutral macro-tetrahedra, [B18S27]0± and [B32S48]0± [4], while the ternary CaB2S4 consists of three-dimensional linkage of BS4-tetrahedra with calcium atoms at the center of the S12icosahedra [5]. During our extensive study on the synthesis of ternary thioborate system containing monovalent ions, we have found a new copper thioborate, CuBS2, with the chalcopyrite structure. In this report, we describe the high-pressure synthesis and the crystal structure of CuBS2.
Powders of elemental amorphous boron (99.5% in purity), crystalline orthorhombic sulfur (99%), and cupper sulfide (99%) were used as starting materials. Stoichiometric amounts of Cu2S, B, and S (Cu2S:B2S3 = 1:1) were dry mixed using an agate mortar. The mixed powder was pressed into a pellet form and placed in a cylindrical boron nitride capsule. Then the capsule was inserted into the high-pressure cell assemblage composed of NaCl sleeve and a carbon heater. The detailed cell assemblage of the belt-type high-pressure equipment is described in our earlier paper [6]. High-pressure synthesis was carried out at 3–5 GPa and 700– 1200 °C for 30 min. After high-pressure/temperature reaction, the specimen was quenched to room temperature before releasing the applied pressure. The obtained specimen was analyzed by powder X-ray diffraction technique using a monochromatic CuKα radiation. The crystal structure was refined by the Rietveld analysis of the powder X-ray diffraction data using the RIETAN 2000 program [7]. UV–Vis diffuse reflectance spectrum was recorded by a UV–Vis spectrophotometer (JASCO V-570).
⁎ Corresponding author. Tel.: +81 22 795 7225; fax: +81 22 795 7228. E-mail address: [email protected] (H. Takizawa). 0167-577X/$ - see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2006.09.018
3. Results and discussion A new high-pressure phase, CuBS2, was synthesized at highpressure condition and metastably retained to ambient condition. Nearly single phase CuBS2 was formed at 3 GPa and 700–900 °C. At higher pressure, pyrite-type CuS2 appeared and coexisted with CuBS2.
T. Kajiki et al. / Materials Letters 61 (2007) 2382–2384
Fig. 1. Powder X-ray diffraction profile of CuBS2 synthesized at 3 GPa and 700 °C.
2383
Fig. 4. UV–Vis diffuse reflectance spectrum of CuBS2.
RF = 3.57% with the S-value (corresponding to the goodness-of-fit) of 1.43. The observed, calculated, and the difference plots of the X-ray diffraction data are shown in Fig. 2. The refined atom coordinates are listed in Table 2. Here, the isotropic atomic displacement parameter of B was fixed because it was difficult to refine the parameter for such a light element. Fig. 3 shows the crystal structure of CuBS2. The structure can be regarded as chalcopyrite-type structure consisting of three-dimensional linkage of BS4-tetrahedra. It is known that CuMS2 (M: Al, Ga, and In) crystallizes into the chalcopyrite-type structure under ambient pressure condition [9]. CuBS2 is the first case for chalcopyrite-type compounds consisting of BS4-tetrahedra. Selected interatomic distances and bond angles of CuBS2 are given in Table 3 along with the data for other Fig. 2. X-ray Rietveld refinement profiles for CuBS2. Points are the observed data and solid line is the calculated profile. Marks below the profile show the allowed reflections. The difference curve, observed–calculated, is plotted beneath.
Fig. 1 shows the powder X-ray diffraction profile of CuBS2 synthesized at 3 GPa and 700 °C. The diffraction lines of CuBS2 were completely indexed on a tetragonal unit cell with lattice parameters of a = 0.5044(1) nm and c = 0.8947(2) nm. From the systematic extinctions, hkl; h + k + l = 2n, hk0; h + k = 2n, 0kl; k + l = 2n, and 00l; l = 4n, possible space group was selected to be I41md (no. 109) or I-42d (no. 122). The latter space group is identical with that of the chalcopyritetype compound, CuAlS2 [8]. The crystal structure refinement was carried out for 232 reflections by applying the structure model of CuAlS2 [8]. Table 1 lists the data collection and the refinement conditions for the Rietveld analysis. The final refinement gave reliability factors of RWP = 6.98%, RI = 4.28%, and
Table 1 Powder X-ray Rietveld refinement for CuBS2 Chemical formula Formula weight Space group a (nm) c (nm) Z Dcalc (g/cm3) Powder color X-ray radiation Monochromator 2θ range (°) Step width (°) No. of points Counting time (s/step) Temperature (K) No. of reflections No. of refined parameters Reliability factors RWP (%) Rp (%) RI (%) RF (%) S
CuBS2 138.483 I-42d (no. 122) 0.5044(1) 0.8947(2) 4 4.040 Light gray CuKα Graphite 5.00–120.00 0.04 2839 1 293 232 59 6.98 5.11 4.28 3.57 1.43
Table 2 Atom coordinates for CuBS2
Fig. 3. Crystal structure of CuBS2.
Atom
Site
x
y
z
B/10− 2 nm− 2
Cu B S
4a 4b 8d
0.0 0.0 0.3083(5)
0.0 0.0 0.25
0.0 0.5 0.125
0.75(9) 1.0 0.59(10)
2384
T. Kajiki et al. / Materials Letters 61 (2007) 2382–2384
Table 3 Bond distances and angles in CuBS2 along with isomorphous CuMS2 (M = Al, Ga, and In) CuBS2 Lattice parameters/ nm a c c/a Interatomic distances/nm Cu–S M–S Bond angles/° S–Cu–S ×4 ×2 S–M–S ×4 ×2 a
CuAlS2a
CuGaS2a
CuInS2a
0.5044(1) 0.8947(2) 1.77
0.5312 1.042 1.96
0.5349 1.047 1.96
0.5517 1.006 1.82
0.2293(1) 0.1943(1)
0.2351 0.2239
0.2380 0.2224
0.2288 0.2517
under high-pressure condition. Consequently, the compound exhibits large deviation (c / a = 1.77) from the ideal chalcopyrite-type structure (c / a = 2.0). Fig. 4 shows the UV–Vis diffuse reflectance spectrum of CuBS2. The optical band gap is estimated to be Eg = 3.61 eV. The value is the largest among the existing chalcopyrite-type compounds. The detailed characterization of this new phase is now under progress and will be reported in the near future.
Acknowledgment
103.75(2) 121.63(5) 109.34(3) 109.72(5)
108.0 112.5 108.7 109.9
107.5 113.5 108.2 110.1
105.2 111.6 107.7 112.9
This work has been supported by a Grant-in-Aid for Scientific Research from the Ministry of Education, Culture, Sports, Science and Technology, Japan. References
Data from Ref. [9].
chalcopyrites, CuMS2 (M: Al, Ga, and In) [9]. The B–S bond length (0.1943(1) nm) is slightly longer, but a permissible value, as compared to those (∼ 0.192 nm) in other ternary thioborates built up from tetrahedral boron atoms [2,5]. The value is also comparable with the sum of the covalent radii (B–S: 0.192 nm). It should be noted that the average S–B–S bond angle is 109.47°, in good agreement with the ideal sp3-hybridized bond angle, suggesting a strong covalent character of the B–S bonds. The Cu–S bond length in CuBS2 (0.2293(1) nm) is in good agreement with other CuMS2, however, S–Cu–S bond angles, 103.75(2)°and 121.63(5)°, show large deviation from the ideal tetrahedral angle. Such distortion is due to the large difference in ionic (and/or covalent) radius between boron and copper. That is, the boron atom is too small to replace cation sites of zincblende-type sub-lattice, and this is why the compound could be stabilized only
[1] B. Bertermann, W.M. Warmuth, C. Jansen, F. Hiltmann, B. Krebs, Solid State Ionics 117 (1999) 245. [2] O. Conrad, C. Jansen, B. Krebs, Angew. Chem. Int. Ed. 37 (1998) 3208. [3] T. Sasaki, H. Takizawa, K. Uheda, T. Endo, Phys. Status Solidi, B 223 (2001) 29. [4] T. Sasaki, H. Takizawa, K. Uheda, T. Yanashita, T. Endo, J. Solid State Chem. 166 (2002) 164. [5] T. Sasaki, H. Takizawa, T. Takeda, T. Endo, Mater. Res. Bull. 38 (2003) 33. [6] H. Takizawa, T. Sato, T. Endo, M. Shimada, J. Solid State Chem. 68 (1987) 234. [7] F. Izumi, T. Ikeda, Mater. Sci. Forum 321–324 (2000) 198. [8] H. Hahn, G. Frank, W. Klingler, A.D. Meyer, G. Störger, Z. Anorg, Allg. Chem. 271 (1953) 153. [9] H.W. Spiess, U. Haeberlen, G. Brandt, A. Räuber, J. Schneider, Phys. Status Solidi, B 62 (1974) 183.
High-pressure synthesis of a new copper thioborate, CuBS2 Takahiro Kajiki, Yamato Hayashi, Hirotsugu Takizawa ⁎ Department of Applied Chemistry, Graduate School of Engineering, Tohoku University, Aoba-yama 07, Sendai 980-8579, Japan Received 2 June 2006; accepted 7 September 2006 Available online 26 September 2006
Abstract A new copper thioborate, CuBS2, was synthesized at high-pressure/temperature condition of 3 GPa and 700–900 °C. The crystal structure was refined by the Rietveld analysis of the powder X-ray diffraction data. The compound crystallizes into a tetragonal unit cell (a = 0.5044(1) nm, c = 0.8947(2) nm, space group: I-42d), isostructural with CuMS2 chalcopyrite compounds (M: Al, Ga, and In). The compound is the first representative of the chalcopyrite-type family consisting of BS4-tetrahedra. From the UV–Vis diffuse reflectance spectrum, the optical band gap of CuBS2 was estimated to be Eg = 3.61 eV. © 2006 Elsevier B.V. All rights reserved. Keywords: Crystal structure; Intermetallic alloys and compounds; High-pressure synthesis; Rietveld analysis; Chalcopyrite
1. Introduction
2. Experimental
Recently, a number of ternary thioborates (MxBySz: metal borosulfides) have been synthesized. Among these thioborates, compounds containing lithium have been extensively investigated for the specific application to super ionic conducting materials [1,2]. Some of these crystalline thioborates consist of characteristic “macro-tetrahedral” structural units represented by formulas of [B4S10]8− or [B10S18]6−. These macro-tetrahedra have shapes of large pyramidal structures built up from covalent BS4-tetrahedra. We have previously examined the high-pressure synthesis of binary B–S and ternary thioborate systems and successfully synthesized some new high-pressure phases, BS [3], B2S3 [4], and CaB2S4 [5]. The results suggest that the formation of BS4tetrahedra (tetrahedral boron atom) is favored under high-pressure condition. The binary compound, B2S3, is built up from two kinds of electrically neutral macro-tetrahedra, [B18S27]0± and [B32S48]0± [4], while the ternary CaB2S4 consists of three-dimensional linkage of BS4-tetrahedra with calcium atoms at the center of the S12icosahedra [5]. During our extensive study on the synthesis of ternary thioborate system containing monovalent ions, we have found a new copper thioborate, CuBS2, with the chalcopyrite structure. In this report, we describe the high-pressure synthesis and the crystal structure of CuBS2.
Powders of elemental amorphous boron (99.5% in purity), crystalline orthorhombic sulfur (99%), and cupper sulfide (99%) were used as starting materials. Stoichiometric amounts of Cu2S, B, and S (Cu2S:B2S3 = 1:1) were dry mixed using an agate mortar. The mixed powder was pressed into a pellet form and placed in a cylindrical boron nitride capsule. Then the capsule was inserted into the high-pressure cell assemblage composed of NaCl sleeve and a carbon heater. The detailed cell assemblage of the belt-type high-pressure equipment is described in our earlier paper [6]. High-pressure synthesis was carried out at 3–5 GPa and 700– 1200 °C for 30 min. After high-pressure/temperature reaction, the specimen was quenched to room temperature before releasing the applied pressure. The obtained specimen was analyzed by powder X-ray diffraction technique using a monochromatic CuKα radiation. The crystal structure was refined by the Rietveld analysis of the powder X-ray diffraction data using the RIETAN 2000 program [7]. UV–Vis diffuse reflectance spectrum was recorded by a UV–Vis spectrophotometer (JASCO V-570).
⁎ Corresponding author. Tel.: +81 22 795 7225; fax: +81 22 795 7228. E-mail address: [email protected] (H. Takizawa). 0167-577X/$ - see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2006.09.018
3. Results and discussion A new high-pressure phase, CuBS2, was synthesized at highpressure condition and metastably retained to ambient condition. Nearly single phase CuBS2 was formed at 3 GPa and 700–900 °C. At higher pressure, pyrite-type CuS2 appeared and coexisted with CuBS2.
T. Kajiki et al. / Materials Letters 61 (2007) 2382–2384
Fig. 1. Powder X-ray diffraction profile of CuBS2 synthesized at 3 GPa and 700 °C.
2383
Fig. 4. UV–Vis diffuse reflectance spectrum of CuBS2.
RF = 3.57% with the S-value (corresponding to the goodness-of-fit) of 1.43. The observed, calculated, and the difference plots of the X-ray diffraction data are shown in Fig. 2. The refined atom coordinates are listed in Table 2. Here, the isotropic atomic displacement parameter of B was fixed because it was difficult to refine the parameter for such a light element. Fig. 3 shows the crystal structure of CuBS2. The structure can be regarded as chalcopyrite-type structure consisting of three-dimensional linkage of BS4-tetrahedra. It is known that CuMS2 (M: Al, Ga, and In) crystallizes into the chalcopyrite-type structure under ambient pressure condition [9]. CuBS2 is the first case for chalcopyrite-type compounds consisting of BS4-tetrahedra. Selected interatomic distances and bond angles of CuBS2 are given in Table 3 along with the data for other Fig. 2. X-ray Rietveld refinement profiles for CuBS2. Points are the observed data and solid line is the calculated profile. Marks below the profile show the allowed reflections. The difference curve, observed–calculated, is plotted beneath.
Fig. 1 shows the powder X-ray diffraction profile of CuBS2 synthesized at 3 GPa and 700 °C. The diffraction lines of CuBS2 were completely indexed on a tetragonal unit cell with lattice parameters of a = 0.5044(1) nm and c = 0.8947(2) nm. From the systematic extinctions, hkl; h + k + l = 2n, hk0; h + k = 2n, 0kl; k + l = 2n, and 00l; l = 4n, possible space group was selected to be I41md (no. 109) or I-42d (no. 122). The latter space group is identical with that of the chalcopyritetype compound, CuAlS2 [8]. The crystal structure refinement was carried out for 232 reflections by applying the structure model of CuAlS2 [8]. Table 1 lists the data collection and the refinement conditions for the Rietveld analysis. The final refinement gave reliability factors of RWP = 6.98%, RI = 4.28%, and
Table 1 Powder X-ray Rietveld refinement for CuBS2 Chemical formula Formula weight Space group a (nm) c (nm) Z Dcalc (g/cm3) Powder color X-ray radiation Monochromator 2θ range (°) Step width (°) No. of points Counting time (s/step) Temperature (K) No. of reflections No. of refined parameters Reliability factors RWP (%) Rp (%) RI (%) RF (%) S
CuBS2 138.483 I-42d (no. 122) 0.5044(1) 0.8947(2) 4 4.040 Light gray CuKα Graphite 5.00–120.00 0.04 2839 1 293 232 59 6.98 5.11 4.28 3.57 1.43
Table 2 Atom coordinates for CuBS2
Fig. 3. Crystal structure of CuBS2.
Atom
Site
x
y
z
B/10− 2 nm− 2
Cu B S
4a 4b 8d
0.0 0.0 0.3083(5)
0.0 0.0 0.25
0.0 0.5 0.125
0.75(9) 1.0 0.59(10)
2384
T. Kajiki et al. / Materials Letters 61 (2007) 2382–2384
Table 3 Bond distances and angles in CuBS2 along with isomorphous CuMS2 (M = Al, Ga, and In) CuBS2 Lattice parameters/ nm a c c/a Interatomic distances/nm Cu–S M–S Bond angles/° S–Cu–S ×4 ×2 S–M–S ×4 ×2 a
CuAlS2a
CuGaS2a
CuInS2a
0.5044(1) 0.8947(2) 1.77
0.5312 1.042 1.96
0.5349 1.047 1.96
0.5517 1.006 1.82
0.2293(1) 0.1943(1)
0.2351 0.2239
0.2380 0.2224
0.2288 0.2517
under high-pressure condition. Consequently, the compound exhibits large deviation (c / a = 1.77) from the ideal chalcopyrite-type structure (c / a = 2.0). Fig. 4 shows the UV–Vis diffuse reflectance spectrum of CuBS2. The optical band gap is estimated to be Eg = 3.61 eV. The value is the largest among the existing chalcopyrite-type compounds. The detailed characterization of this new phase is now under progress and will be reported in the near future.
Acknowledgment
103.75(2) 121.63(5) 109.34(3) 109.72(5)
108.0 112.5 108.7 109.9
107.5 113.5 108.2 110.1
105.2 111.6 107.7 112.9
This work has been supported by a Grant-in-Aid for Scientific Research from the Ministry of Education, Culture, Sports, Science and Technology, Japan. References
Data from Ref. [9].
chalcopyrites, CuMS2 (M: Al, Ga, and In) [9]. The B–S bond length (0.1943(1) nm) is slightly longer, but a permissible value, as compared to those (∼ 0.192 nm) in other ternary thioborates built up from tetrahedral boron atoms [2,5]. The value is also comparable with the sum of the covalent radii (B–S: 0.192 nm). It should be noted that the average S–B–S bond angle is 109.47°, in good agreement with the ideal sp3-hybridized bond angle, suggesting a strong covalent character of the B–S bonds. The Cu–S bond length in CuBS2 (0.2293(1) nm) is in good agreement with other CuMS2, however, S–Cu–S bond angles, 103.75(2)°and 121.63(5)°, show large deviation from the ideal tetrahedral angle. Such distortion is due to the large difference in ionic (and/or covalent) radius between boron and copper. That is, the boron atom is too small to replace cation sites of zincblende-type sub-lattice, and this is why the compound could be stabilized only
[1] B. Bertermann, W.M. Warmuth, C. Jansen, F. Hiltmann, B. Krebs, Solid State Ionics 117 (1999) 245. [2] O. Conrad, C. Jansen, B. Krebs, Angew. Chem. Int. Ed. 37 (1998) 3208. [3] T. Sasaki, H. Takizawa, K. Uheda, T. Endo, Phys. Status Solidi, B 223 (2001) 29. [4] T. Sasaki, H. Takizawa, K. Uheda, T. Yanashita, T. Endo, J. Solid State Chem. 166 (2002) 164. [5] T. Sasaki, H. Takizawa, T. Takeda, T. Endo, Mater. Res. Bull. 38 (2003) 33. [6] H. Takizawa, T. Sato, T. Endo, M. Shimada, J. Solid State Chem. 68 (1987) 234. [7] F. Izumi, T. Ikeda, Mater. Sci. Forum 321–324 (2000) 198. [8] H. Hahn, G. Frank, W. Klingler, A.D. Meyer, G. Störger, Z. Anorg, Allg. Chem. 271 (1953) 153. [9] H.W. Spiess, U. Haeberlen, G. Brandt, A. Räuber, J. Schneider, Phys. Status Solidi, B 62 (1974) 183.