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Studies on synthesis and growth mechanism of high quality sheet cubic diamond crystals under high pressure and high temperature conditions
Int. Journal of Refractory Metals and Hard Materials 48 (2014) 61–64
Contents lists available at ScienceDirect
Int. Journal of Refractory Metals and Hard Materials journal homepage: www.elsevier.com/locate/IJRMHM
Studies on synthesis and growth mechanism of high quality sheet cubic diamond crystals under high pressure and high temperature conditions Hu Meihua a,⁎, Bi Ning b, Li Shangsheng a, Su Taichao a, Hu Qiang a, Jia Xiaopeng c, Ma Hongan c a b c
School of Materials Science and Engineering, Henan Polytechnic University, Jiaozuo 454000, China School of Physics and Chemistry, Henan Polytechnic University, Jiaozuo 454000, China State Key Laboratory of Superhard Materials, Jilin University, Changchun 130012, China
a r t i c l e
i n f o
Article history: Received 7 April 2014 Accepted 19 July 2014 Available online 2 August 2014 Keywords: Diamond High pressure and high temperature Temperature gradient Finite element simulation
a b s t r a c t This paper reported the synthesis of high quality sheet cubic diamond crystals by temperature gradient method under high pressure and high temperature conditions with FeNi alloy as solvent catalyst. The growth mechanisms were discussed by finite element simulation. The synthetic sheet cubic diamond crystals had a higher growth rate in radial direction than that in axial direction. Raman spectrum and Fourier transform infrared spectrum indicated that synthesized sheet cubic diamonds had fewer crystal lattice distortions and nitrogen impurities. Finite element simulations indicated that the solvent metal convection field in the radial direction was stronger than that in the axial direction. A mechanism of sheet cubic diamond crystal growth was proposed and discussed. © 2014 Elsevier Ltd. All rights reserved.
Introduction Diamond, as one of the superhard materials, is of great importance in science and technology with applications in cutting and polishing tools, coatings and abrasives, etc. Since the diamond crystals were synthesized in the 1950s [1], many progresses on diamond synthesis and research have been achieved. Two widely used methods are high pressure and high temperature (HPHT) and chemical vapor deposition (CVD) [2–7]. If some transition metals like Fe, Ni, Co, Mn, and their alloy are used as solvent catalyst, typical growth conditions for diamond synthesis are pressures in the range of 5.0–8.0 GPa and temperatures in the range of 1300–1800 °C [8–11]. Among many synthetic methods, the temperature gradient method (TGM) under high pressure and high temperature conditions to synthesize high quality large diamond crystals has been used for several decades and is one of the effective ways for scientific research and commercial production. As we all know, natural diamond crystals are mainly composed by (111) and (110) crystal faces, almost no (100) crystal faces. Therefore, cubic diamond crystals composed of (100) crystal faces only can be obtained by synthesis. Generally, in the P-T phase diagram of carbon, the district for diamond growth is a V-shape region bounded by diamondgraphite equilibrium line and solvent-carbon eutectic melting line in the metal solvent-carbon system [12]. In the region, the shape of diamond crystal is mainly affected by synthetic temperature. Because of different crystal shapes, diamond crystals have many different applications. For example, tower shape diamond crystals with (111) crystal ⁎ Corresponding author. E-mail address: [email protected] (H. Meihua).
http://dx.doi.org/10.1016/j.ijrmhm.2014.07.034 0263-4368/© 2014 Elsevier Ltd. All rights reserved.
faces can be used as the anvil of diamond anvil cell (DAC) or jewelry. High quality large cubic diamonds with sheet shape, which are composed of (100) crystal faces, are widely used in many fields. Many precision and ultra-precision machining tools need regular sheet cubic shape and no inclusions diamond crystals. It has also been used for the heat spreader of the high power laser and windows of infrared instruments. In this work, we systematically studied the synthesis of high quality cubic diamond crystals using temperature gradient method under high pressure and high temperature conditions with FeNi alloy as solvent catalyst. The diamond crystals were characterized by optical microscopes (OM), Raman spectroscopy and Fourier transform infrared (FTIR) spectroscopy. Finite element method (FEM) was used to simulate the solvent metal convection field of the growth cell, and it provided an interesting result to help us understand the growth mechanism of diamond. Experiments The diamond synthetic experiments were performed in a China type SPD-6 × 1200 cubic-anvil high pressure apparatus (CHPA). The assembly schematic diagram of high pressure synthesis cell by temperature gradient method is shown in Fig. 1. High purity graphite powder (99.9%, purity) was selected as carbon source, which was placed in the high temperature region of the growth cell. High quality synthetic type Ib diamond crystals were used as seed crystals, with (100) crystal face of about 0.8 × 0.8 mm2 as the initial growth face, which were placed in the low temperature region of the growth cell. The FeNi alloy (Fe:Ni = 64:36, weight ratio, and 99.9%, purity) was used as the solvent metal. In addition,
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It is clearly shown in Fig. 2 that the synthesized diamond crystals in the FeNi alloy–carbon system are predominantly composed by (100) crystal faces. Most of those crystals are sheet cubic shape with the color of light yellow and few inclusions. Growth rate of sheet cubic diamond crystals
Fig. 1. Sample assembly schematic diagram for diamond growth.
the pressure was estimated by the oil press load, which was calibrated by a curve that was established on the pressure-induced phase transitions of Bi, Tl and Ba; the temperature was determined by a Pt6%Rh–Pt30%Rh thermocouple, respectively [13]. The samples, which taken out from the high pressure apparatus, were put into boiling acids to remove the impurities remaining on these surfaces of diamond crystals. Optical microscope was used to observe the morphology of crystal and inclusion in the diamond crystals. Raman spectrometer and Fourier transform infrared spectrometer were used to characterize the quality of diamond crystals. The solvent metal convection field in the growth cell was simulated by finite element method [14,15]. Using solid 69 and fluid 142 cells in finite element software, thermal–electrical-fluid finite element analyses were carried out in the whole model of the growth cell, respectively. Results and discussion Synthesis of sheet cubic diamond crystals Experiments in the FeNi alloy–carbon system for diamond synthesis were performed at pressures in the range of 5.5–5.8 GPa and temperatures in the range of 1300–1360 °C. The obtained results are summarized in Table 1. During the diamond growth process by TGM, the morphology of diamond changes from cubic crystal mainly with (100) crystal faces, cubo-octahedral crystal mainly with (100) and (111) crystal faces, to octahedral crystals mainly with (111) crystal faces with the increase of synthetic temperature. If the synthetic temperature is too low, that is to say, the region of diamond crystal is close to the left of V-shape region, then, the skeleton crystals may appear (S1). However, if the synthetic temperature is a little higher, the synthesized diamond crystals may show cubo-octahedral shape (S5, S6). From Table 1, sheet cubic diamond crystals are synthesized in our self-designed FeNi alloy–carbon systems at temperature of 1310–1325 °C (S2–S4). It shows that the growth region of high quality sheet cubic diamond crystals is very narrow in the P-T regions of diamond synthesis. Table 1 Experimental results of sheet cubic diamond crystal synthesis. Sample
Pressure (GPa)
Temperature (°C)
Morphology
Rr (mm/h)
Ra (mm/h)
Rr/Ra
S1 S2 S3 S4 S5 S6 S7 S8 S9
5.5 5.5 5.5 5.5 5.5 5.5 5.5 5.7 5.8
1300 1310 1315 1325 1330 1340 1360 1315 1315
/ (100) (100) (100) (100),(111) (100),(111) (111) (100) (100)
/ 0.21 0.21 0.20 0.19 0.18 0.18 0.23 0.24
/ 0.08 0.09 0.10 0.11 0.15 0.16 0.14 0.17
/ 2.63 2.33 2.00 1.73 1.20 1.13 1.64 1.41
Rr: Radial growth rate, Ra: Axial growth rate.
Based on the theory of temperature gradient method of diamond synthesis, the growth rate is mainly affected by the temperature gradient [16,17]. Meanwhile, temperature gradient of diamond synthesis can be adjusted by the growth cell assembly freely. According to the relationship between the morphology of diamond crystal and V-shape regions of diamond synthesis, low temperature section of V-shape regions is suitable for the cubic diamond crystal synthesis by temperature gradient method under HPHT. High growth rate can reduce the synthetic time and cost. However, the growth rate cannot be enhanced without precondition and must be controlled within certain limits. Based on previous studies [18], too high growth rate is not good for the quality of crystal. In addition, the P-T regions of diamond synthesis in the metallic solvent catalyst-carbon systems appeared significantly broader with the increase of pressures. However, the ratio of radial growth rate (Rr) to axial growth rate (Ra) decreases (S8 and S9) with increases of synthetic pressure. In other words, a higher synthesized pressure is not suitable for synthesizing diamond crystals with the high ratio of Rr to Ra. Characterization of sheet cubic diamond crystals by Raman and FTIR spectroscopies Raman spectroscopy was used to characterize crystal lattice distortion or crystalline quality of diamond crystals. For comparison, two diamond crystals synthesized from our lab (a) and purchased from commercial company (b) were selected to be analyzed by Raman spectroscopy. Fig. 3 shows Raman spectra recorded from diamond crystals. The Raman peak values and the full width at half maximum (FWHM) indicated the relative quality of those crystals. The diamond Raman peaks values of those diamond crystals are near 1332 cm−1. However, the FWHM of 1332 cm−1 peak of our diamond sample (a) is smaller than that of the commercial diamond (b). It is supposed that the observed features of the Raman spectrum of diamond are related to the increasing concentrations of micro-crystallites in boundary, impurities, residual stress, or defects, etc. Therefore, it illustrates that the sheet cubic diamond crystals synthesized in this paper have less lattice distortion and with high quality. On the other hand, nitrogen is one of the main impurities in diamond crystal and nitrogen concentration is determined to be in substitutional form based on the shape of spectrum in the one phonon region (800–1400 cm−1) [19]. FTIR spectrum of diamond crystal is shown in Fig. 4. This spectrum shows that the absorption intensity of sheet cubic diamond crystal is in one phonon region. Generally, the nitrogen concentration of normal diamond crystal is about 200–800 ppm. The nitrogen concentration of our samples is about 240 ppm. Compared with normal diamond crystals, our sample has less nitrogen impurity, and it is of high quality. Simulation of growth mechanism by FEM In order to analyze the growth mechanism of sheet cubic diamonds, FEM was used to simulate the growth process of diamond crystal. As shown in Fig. 5, the solvent metal convection field of the growth cell of sheet cubic diamond crystal was simulated by FEM. Diffusion and convection in crystal growth cell provide carbon transport from the source to the crystal surface, and it is the governing driving force of crystal growth. The results of theoretical simulation indicate that distribution of solvent metal convection field shows visible difference in diamond growth
H. Meihua et al. / Int. Journal of Refractory Metals and Hard Materials 48 (2014) 61–64
63
Fig. 2. OM photographs of sheet cubic diamond crystals synthesized in the FeNi alloy–carbon system at 5.5 GPa and 1310 °C.
cell and the convection intensity in edge of the cavity is stronger than that in the center. The growth mechanism of sheet cubic diamond can be explained as follows: The capability of carbon transportation is affected by the convection intensity. Because the seed crystal is bedded in the center of growth cell, in the axial direction, convection intensity is weak, and the growth rate is slow. However, in the radial direction, convection intensity is strong, and the growth rate is fast. As a
conclusion, the growth rate in the radial direction is higher than that in the axial direction, the grown diamond crystal shows the sheet cubic shape.
Conclusions High quality sheet cubic diamond crystals were successfully synthesized by temperature gradient method under high pressure and high temperature conditions. The growth region of high quality sheet cubic diamond crystals was very narrow in the P-T regions of diamond synthesis. Sheet cubic diamond crystals had higher ratio in size of radial direction than axial direction, which mainly resulted from the higher radial growth rate than axial growth rate. Raman spectra and Fourier transform infrared spectrum indicated that our synthesized sheet cubic diamond crystals had high quality. Finite element simulation results were consistent with the experiment obtained; and explained the growth mechanism of sheet cubic diamond crystals.
Acknowledgments This work is supported by the Doctoral Fund of Henan Polytechnic University (Grant No. 60607/005) and the Program for Innovative Research Team of Henan Polytechnic University (T2013-4).
Fig. 3. Raman spectra of two diamond crystals synthesized from our lab (a) and purchased from commercial company (b).
Fig. 4. Infrared absorption spectrum of sheet cubic diamond crystals.
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Fig. 5. Solvent metal convection field of the sheet cubic diamond growth cell.
References [1] Bundy FP, Hall HT, Strong HM, Wentorf RH. Man-made diamonds. Nature 1955;176: 51–5. [2] Sumiya H, Satoh S. High-pressure synthesis of high-purity diamond. Diamond Relat Mater 1996;5:1359–65. [3] Burns RC, Hansen JO, Spits RA, Sibanda M, Welbourn CM, Welch DL. Growth of high purity large synthetic diamond crystals. Diamond Relat Mater 1999;8:1433–7. [4] Meng YF, Yan CS, Lai J, Krasnicki S, Shu HY, Yu T. Enhanced optical properties of chemical vapor deposited single crystal diamond by low-pressure/high-temperature annealing. PANS 2008;105:17620–5. [5] Sumiya H, Satoh S. Synthesis of polycrystalline diamond with new non-metallic catalyst under high pressure and high temperature. Int J Refract Met Hard Mater 1999;17:345–50. [6] Sumiya H, Harano K. Distinctive mechanical properties of nano-polycrystalline diamond synthesized by direct conversion sintering under HPHT. Diamond Relat Mater 2012;24:44–8. [7] Li Y, Jia XP, Shi W, Leng SL, Ma HA, Sun SS, et al. The preparation of new “BCN” diamond under higher pressure and higher temperature. Int J Refract Met Hard Mater 2014;43:147–9. [8] Palyanov YN, Khokhryakov AF, Borzdov YM, Kupriyanov IN. Diamond growth and morphology under the influence of impurity adsorption. Cryst Growth Des 2013; 13:5411–9. [9] Lin IC, Lin CJ, Tuan WH. Growth of diamond crystals in Fe–Ni metallic catalysis. Diamond Relat Mater 2011;20:42–7. [10] Bormashov VS, Tarelkin SA, Buga SG, Kuznetsov MS, Terentiev SA, Semenov AN, et al. Electrical properties of the high quality boron-doped synthetic single-crystal
[11]
[12]
[13]
[14]
[15]
[16] [17] [18]
[19]
diamonds grown by the temperature gradient method. Diamond Relat Mater 2013;35:19–23. Hu MH, Jia XP, Yan BM, Li Y, Zhu CY, Ma HA. Understanding of the shape-controlled synthesis of strip shape diamond under high pressure and high temperature conditions. Int J Refract Met Hard Mater 2012;30:85–90. Liu XB, Jia XP, Guo XK, Zhang ZF, Ma HA. Experimental evidence for nucleation and growth mechanism of diamond by seed-assisted method at high pressure and high temperature. Cryst Growth Des 2010;10:2895–900. Ma HA, Jia XP, Chen LX, Zhu PW, Guo WL, Guo XB, et al. High-pressure pyrolysis study of C3N6H6: a route to preparing bulk C3N4. J Phys Condens Matter 2002;14: 11269–73. Demina SE, Kalaev VV, Lysakovskyi VV, Serga MA, Kovalenko TV, Ivahnenko SA. Computer modeling of diamond single crystal growth by the temperature gradient method in carbon-solvent system. J Cryst Growth 2009;311:680–3. Han QG, Li MZ, Jia XP, Ma HA, Li YF. Modeling of effective design of high pressure anvils used for large scale commercial production of gem quality large single crystal diamond. Diamond Relat Mater 2011;20:969–73. Wentorf RH. Some studies of diamond growth rates. J Phys Chem 1971;75:1833–7. Strong HM, Chrenko RM. Further studies on diamond growth rates and physical properties of laboratory-made diamond. J Phys Chem 1971;75:1838–43. Tian Y, Jia XP, Zang CY, Li R, Li SS, Xiao HY, et al. Finite element analysis of convection in growth cell for diamond growth using Ni-based solvent. Chin Phys Lett 2009; 26(028104):1–3. Yu RZ, Ma HA, Liang ZZ, Liu WQ, Zheng YJ, Jia XP. HPHT synthesis of diamond with high concentration nitrogen using powder catalyst with additive Ba(N3)2. Diamond Relat Mater 2008;17:180–4.
Contents lists available at ScienceDirect
Int. Journal of Refractory Metals and Hard Materials journal homepage: www.elsevier.com/locate/IJRMHM
Studies on synthesis and growth mechanism of high quality sheet cubic diamond crystals under high pressure and high temperature conditions Hu Meihua a,⁎, Bi Ning b, Li Shangsheng a, Su Taichao a, Hu Qiang a, Jia Xiaopeng c, Ma Hongan c a b c
School of Materials Science and Engineering, Henan Polytechnic University, Jiaozuo 454000, China School of Physics and Chemistry, Henan Polytechnic University, Jiaozuo 454000, China State Key Laboratory of Superhard Materials, Jilin University, Changchun 130012, China
a r t i c l e
i n f o
Article history: Received 7 April 2014 Accepted 19 July 2014 Available online 2 August 2014 Keywords: Diamond High pressure and high temperature Temperature gradient Finite element simulation
a b s t r a c t This paper reported the synthesis of high quality sheet cubic diamond crystals by temperature gradient method under high pressure and high temperature conditions with FeNi alloy as solvent catalyst. The growth mechanisms were discussed by finite element simulation. The synthetic sheet cubic diamond crystals had a higher growth rate in radial direction than that in axial direction. Raman spectrum and Fourier transform infrared spectrum indicated that synthesized sheet cubic diamonds had fewer crystal lattice distortions and nitrogen impurities. Finite element simulations indicated that the solvent metal convection field in the radial direction was stronger than that in the axial direction. A mechanism of sheet cubic diamond crystal growth was proposed and discussed. © 2014 Elsevier Ltd. All rights reserved.
Introduction Diamond, as one of the superhard materials, is of great importance in science and technology with applications in cutting and polishing tools, coatings and abrasives, etc. Since the diamond crystals were synthesized in the 1950s [1], many progresses on diamond synthesis and research have been achieved. Two widely used methods are high pressure and high temperature (HPHT) and chemical vapor deposition (CVD) [2–7]. If some transition metals like Fe, Ni, Co, Mn, and their alloy are used as solvent catalyst, typical growth conditions for diamond synthesis are pressures in the range of 5.0–8.0 GPa and temperatures in the range of 1300–1800 °C [8–11]. Among many synthetic methods, the temperature gradient method (TGM) under high pressure and high temperature conditions to synthesize high quality large diamond crystals has been used for several decades and is one of the effective ways for scientific research and commercial production. As we all know, natural diamond crystals are mainly composed by (111) and (110) crystal faces, almost no (100) crystal faces. Therefore, cubic diamond crystals composed of (100) crystal faces only can be obtained by synthesis. Generally, in the P-T phase diagram of carbon, the district for diamond growth is a V-shape region bounded by diamondgraphite equilibrium line and solvent-carbon eutectic melting line in the metal solvent-carbon system [12]. In the region, the shape of diamond crystal is mainly affected by synthetic temperature. Because of different crystal shapes, diamond crystals have many different applications. For example, tower shape diamond crystals with (111) crystal ⁎ Corresponding author. E-mail address: [email protected] (H. Meihua).
http://dx.doi.org/10.1016/j.ijrmhm.2014.07.034 0263-4368/© 2014 Elsevier Ltd. All rights reserved.
faces can be used as the anvil of diamond anvil cell (DAC) or jewelry. High quality large cubic diamonds with sheet shape, which are composed of (100) crystal faces, are widely used in many fields. Many precision and ultra-precision machining tools need regular sheet cubic shape and no inclusions diamond crystals. It has also been used for the heat spreader of the high power laser and windows of infrared instruments. In this work, we systematically studied the synthesis of high quality cubic diamond crystals using temperature gradient method under high pressure and high temperature conditions with FeNi alloy as solvent catalyst. The diamond crystals were characterized by optical microscopes (OM), Raman spectroscopy and Fourier transform infrared (FTIR) spectroscopy. Finite element method (FEM) was used to simulate the solvent metal convection field of the growth cell, and it provided an interesting result to help us understand the growth mechanism of diamond. Experiments The diamond synthetic experiments were performed in a China type SPD-6 × 1200 cubic-anvil high pressure apparatus (CHPA). The assembly schematic diagram of high pressure synthesis cell by temperature gradient method is shown in Fig. 1. High purity graphite powder (99.9%, purity) was selected as carbon source, which was placed in the high temperature region of the growth cell. High quality synthetic type Ib diamond crystals were used as seed crystals, with (100) crystal face of about 0.8 × 0.8 mm2 as the initial growth face, which were placed in the low temperature region of the growth cell. The FeNi alloy (Fe:Ni = 64:36, weight ratio, and 99.9%, purity) was used as the solvent metal. In addition,
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It is clearly shown in Fig. 2 that the synthesized diamond crystals in the FeNi alloy–carbon system are predominantly composed by (100) crystal faces. Most of those crystals are sheet cubic shape with the color of light yellow and few inclusions. Growth rate of sheet cubic diamond crystals
Fig. 1. Sample assembly schematic diagram for diamond growth.
the pressure was estimated by the oil press load, which was calibrated by a curve that was established on the pressure-induced phase transitions of Bi, Tl and Ba; the temperature was determined by a Pt6%Rh–Pt30%Rh thermocouple, respectively [13]. The samples, which taken out from the high pressure apparatus, were put into boiling acids to remove the impurities remaining on these surfaces of diamond crystals. Optical microscope was used to observe the morphology of crystal and inclusion in the diamond crystals. Raman spectrometer and Fourier transform infrared spectrometer were used to characterize the quality of diamond crystals. The solvent metal convection field in the growth cell was simulated by finite element method [14,15]. Using solid 69 and fluid 142 cells in finite element software, thermal–electrical-fluid finite element analyses were carried out in the whole model of the growth cell, respectively. Results and discussion Synthesis of sheet cubic diamond crystals Experiments in the FeNi alloy–carbon system for diamond synthesis were performed at pressures in the range of 5.5–5.8 GPa and temperatures in the range of 1300–1360 °C. The obtained results are summarized in Table 1. During the diamond growth process by TGM, the morphology of diamond changes from cubic crystal mainly with (100) crystal faces, cubo-octahedral crystal mainly with (100) and (111) crystal faces, to octahedral crystals mainly with (111) crystal faces with the increase of synthetic temperature. If the synthetic temperature is too low, that is to say, the region of diamond crystal is close to the left of V-shape region, then, the skeleton crystals may appear (S1). However, if the synthetic temperature is a little higher, the synthesized diamond crystals may show cubo-octahedral shape (S5, S6). From Table 1, sheet cubic diamond crystals are synthesized in our self-designed FeNi alloy–carbon systems at temperature of 1310–1325 °C (S2–S4). It shows that the growth region of high quality sheet cubic diamond crystals is very narrow in the P-T regions of diamond synthesis. Table 1 Experimental results of sheet cubic diamond crystal synthesis. Sample
Pressure (GPa)
Temperature (°C)
Morphology
Rr (mm/h)
Ra (mm/h)
Rr/Ra
S1 S2 S3 S4 S5 S6 S7 S8 S9
5.5 5.5 5.5 5.5 5.5 5.5 5.5 5.7 5.8
1300 1310 1315 1325 1330 1340 1360 1315 1315
/ (100) (100) (100) (100),(111) (100),(111) (111) (100) (100)
/ 0.21 0.21 0.20 0.19 0.18 0.18 0.23 0.24
/ 0.08 0.09 0.10 0.11 0.15 0.16 0.14 0.17
/ 2.63 2.33 2.00 1.73 1.20 1.13 1.64 1.41
Rr: Radial growth rate, Ra: Axial growth rate.
Based on the theory of temperature gradient method of diamond synthesis, the growth rate is mainly affected by the temperature gradient [16,17]. Meanwhile, temperature gradient of diamond synthesis can be adjusted by the growth cell assembly freely. According to the relationship between the morphology of diamond crystal and V-shape regions of diamond synthesis, low temperature section of V-shape regions is suitable for the cubic diamond crystal synthesis by temperature gradient method under HPHT. High growth rate can reduce the synthetic time and cost. However, the growth rate cannot be enhanced without precondition and must be controlled within certain limits. Based on previous studies [18], too high growth rate is not good for the quality of crystal. In addition, the P-T regions of diamond synthesis in the metallic solvent catalyst-carbon systems appeared significantly broader with the increase of pressures. However, the ratio of radial growth rate (Rr) to axial growth rate (Ra) decreases (S8 and S9) with increases of synthetic pressure. In other words, a higher synthesized pressure is not suitable for synthesizing diamond crystals with the high ratio of Rr to Ra. Characterization of sheet cubic diamond crystals by Raman and FTIR spectroscopies Raman spectroscopy was used to characterize crystal lattice distortion or crystalline quality of diamond crystals. For comparison, two diamond crystals synthesized from our lab (a) and purchased from commercial company (b) were selected to be analyzed by Raman spectroscopy. Fig. 3 shows Raman spectra recorded from diamond crystals. The Raman peak values and the full width at half maximum (FWHM) indicated the relative quality of those crystals. The diamond Raman peaks values of those diamond crystals are near 1332 cm−1. However, the FWHM of 1332 cm−1 peak of our diamond sample (a) is smaller than that of the commercial diamond (b). It is supposed that the observed features of the Raman spectrum of diamond are related to the increasing concentrations of micro-crystallites in boundary, impurities, residual stress, or defects, etc. Therefore, it illustrates that the sheet cubic diamond crystals synthesized in this paper have less lattice distortion and with high quality. On the other hand, nitrogen is one of the main impurities in diamond crystal and nitrogen concentration is determined to be in substitutional form based on the shape of spectrum in the one phonon region (800–1400 cm−1) [19]. FTIR spectrum of diamond crystal is shown in Fig. 4. This spectrum shows that the absorption intensity of sheet cubic diamond crystal is in one phonon region. Generally, the nitrogen concentration of normal diamond crystal is about 200–800 ppm. The nitrogen concentration of our samples is about 240 ppm. Compared with normal diamond crystals, our sample has less nitrogen impurity, and it is of high quality. Simulation of growth mechanism by FEM In order to analyze the growth mechanism of sheet cubic diamonds, FEM was used to simulate the growth process of diamond crystal. As shown in Fig. 5, the solvent metal convection field of the growth cell of sheet cubic diamond crystal was simulated by FEM. Diffusion and convection in crystal growth cell provide carbon transport from the source to the crystal surface, and it is the governing driving force of crystal growth. The results of theoretical simulation indicate that distribution of solvent metal convection field shows visible difference in diamond growth
H. Meihua et al. / Int. Journal of Refractory Metals and Hard Materials 48 (2014) 61–64
63
Fig. 2. OM photographs of sheet cubic diamond crystals synthesized in the FeNi alloy–carbon system at 5.5 GPa and 1310 °C.
cell and the convection intensity in edge of the cavity is stronger than that in the center. The growth mechanism of sheet cubic diamond can be explained as follows: The capability of carbon transportation is affected by the convection intensity. Because the seed crystal is bedded in the center of growth cell, in the axial direction, convection intensity is weak, and the growth rate is slow. However, in the radial direction, convection intensity is strong, and the growth rate is fast. As a
conclusion, the growth rate in the radial direction is higher than that in the axial direction, the grown diamond crystal shows the sheet cubic shape.
Conclusions High quality sheet cubic diamond crystals were successfully synthesized by temperature gradient method under high pressure and high temperature conditions. The growth region of high quality sheet cubic diamond crystals was very narrow in the P-T regions of diamond synthesis. Sheet cubic diamond crystals had higher ratio in size of radial direction than axial direction, which mainly resulted from the higher radial growth rate than axial growth rate. Raman spectra and Fourier transform infrared spectrum indicated that our synthesized sheet cubic diamond crystals had high quality. Finite element simulation results were consistent with the experiment obtained; and explained the growth mechanism of sheet cubic diamond crystals.
Acknowledgments This work is supported by the Doctoral Fund of Henan Polytechnic University (Grant No. 60607/005) and the Program for Innovative Research Team of Henan Polytechnic University (T2013-4).
Fig. 3. Raman spectra of two diamond crystals synthesized from our lab (a) and purchased from commercial company (b).
Fig. 4. Infrared absorption spectrum of sheet cubic diamond crystals.
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Fig. 5. Solvent metal convection field of the sheet cubic diamond growth cell.
References [1] Bundy FP, Hall HT, Strong HM, Wentorf RH. Man-made diamonds. Nature 1955;176: 51–5. [2] Sumiya H, Satoh S. High-pressure synthesis of high-purity diamond. Diamond Relat Mater 1996;5:1359–65. [3] Burns RC, Hansen JO, Spits RA, Sibanda M, Welbourn CM, Welch DL. Growth of high purity large synthetic diamond crystals. Diamond Relat Mater 1999;8:1433–7. [4] Meng YF, Yan CS, Lai J, Krasnicki S, Shu HY, Yu T. Enhanced optical properties of chemical vapor deposited single crystal diamond by low-pressure/high-temperature annealing. PANS 2008;105:17620–5. [5] Sumiya H, Satoh S. Synthesis of polycrystalline diamond with new non-metallic catalyst under high pressure and high temperature. Int J Refract Met Hard Mater 1999;17:345–50. [6] Sumiya H, Harano K. Distinctive mechanical properties of nano-polycrystalline diamond synthesized by direct conversion sintering under HPHT. Diamond Relat Mater 2012;24:44–8. [7] Li Y, Jia XP, Shi W, Leng SL, Ma HA, Sun SS, et al. The preparation of new “BCN” diamond under higher pressure and higher temperature. Int J Refract Met Hard Mater 2014;43:147–9. [8] Palyanov YN, Khokhryakov AF, Borzdov YM, Kupriyanov IN. Diamond growth and morphology under the influence of impurity adsorption. Cryst Growth Des 2013; 13:5411–9. [9] Lin IC, Lin CJ, Tuan WH. Growth of diamond crystals in Fe–Ni metallic catalysis. Diamond Relat Mater 2011;20:42–7. [10] Bormashov VS, Tarelkin SA, Buga SG, Kuznetsov MS, Terentiev SA, Semenov AN, et al. Electrical properties of the high quality boron-doped synthetic single-crystal
[11]
[12]
[13]
[14]
[15]
[16] [17] [18]
[19]
diamonds grown by the temperature gradient method. Diamond Relat Mater 2013;35:19–23. Hu MH, Jia XP, Yan BM, Li Y, Zhu CY, Ma HA. Understanding of the shape-controlled synthesis of strip shape diamond under high pressure and high temperature conditions. Int J Refract Met Hard Mater 2012;30:85–90. Liu XB, Jia XP, Guo XK, Zhang ZF, Ma HA. Experimental evidence for nucleation and growth mechanism of diamond by seed-assisted method at high pressure and high temperature. Cryst Growth Des 2010;10:2895–900. Ma HA, Jia XP, Chen LX, Zhu PW, Guo WL, Guo XB, et al. High-pressure pyrolysis study of C3N6H6: a route to preparing bulk C3N4. J Phys Condens Matter 2002;14: 11269–73. Demina SE, Kalaev VV, Lysakovskyi VV, Serga MA, Kovalenko TV, Ivahnenko SA. Computer modeling of diamond single crystal growth by the temperature gradient method in carbon-solvent system. J Cryst Growth 2009;311:680–3. Han QG, Li MZ, Jia XP, Ma HA, Li YF. Modeling of effective design of high pressure anvils used for large scale commercial production of gem quality large single crystal diamond. Diamond Relat Mater 2011;20:969–73. Wentorf RH. Some studies of diamond growth rates. J Phys Chem 1971;75:1833–7. Strong HM, Chrenko RM. Further studies on diamond growth rates and physical properties of laboratory-made diamond. J Phys Chem 1971;75:1838–43. Tian Y, Jia XP, Zang CY, Li R, Li SS, Xiao HY, et al. Finite element analysis of convection in growth cell for diamond growth using Ni-based solvent. Chin Phys Lett 2009; 26(028104):1–3. Yu RZ, Ma HA, Liang ZZ, Liu WQ, Zheng YJ, Jia XP. HPHT synthesis of diamond with high concentration nitrogen using powder catalyst with additive Ba(N3)2. Diamond Relat Mater 2008;17:180–4.