Effects of hydrogen impurity on diamond crystal growth process Z.F. Zhang a , X.P. Jia a , S.S. Sun a , X.B. Liu b , Y. Li a , B.M. Yan a , H.A. Ma a, ⁎ a National Lab of Superhard Materials, Jilin University, Changchun 130012, China b Department of Earth and Planetary Sciences, Northwestern University, Evanston 847-491-3741, United States abstract article info Article history: Received 14 September 2012 Accepted 17 January 2013 Keywords: Hydrogen impurity Diamond High pressure and high temperature Graphite In this paper, we report the inﬂuence of hydrogen impurity in metal melts on the growth process, morphology, and impurity structure of diamond crystals. In a series of experiments, the hydrogen impurity in the growth system comes from the decomposition of TiH 2 in the HPHT chamber. Diamond growth and morphology are also signiﬁcantly inﬂuenced by the hydrogen impurity. We also note that with increasing hydrogen concentra- tion in the synthetic system from 0.05 wt.% to 0.5 wt.%, the minimum conditions for diamond synthesis in- creased rapidly. The diamond growth processes are suppressed by the excessive TiH 2 additive (0.2 wt.%) and some tiny diamond crystals can be detected by Raman spectroscopy. The effects of the hydrogen on the proper- ties of the crystallization medium have been extensively studied by XRD and Raman spectra. The FTIR spectra of synthesized diamond indicate that the hydrogen atoms can enter the diamond lattice and substitute the carbon atoms in the form of sp 3 \CH 2 \. © 2013 Published by Elsevier Ltd. 1. Introduction In order to get a deep understanding of the mechanism of natural diamond growth, researchers have extensively studied the role of minor elements and impurity on the diamond crystallization process [1–5]. The form and concentration of the impurity signiﬁcantly inﬂu- ence the physical properties of diamond and play an important role in its genesis. The signiﬁcant effects induced by nitrogen impurity on diamond have been investigated for a long time and many works in the literature about this subject can be found. An impurity in diamond as ubiquitous as nitrogen, hydrogen has attracted more attention recently [6–8]. A large number of theoretical and experimental studies have shown that hydrogen impurity has a signiﬁcant inﬂuence on the electronic and thermal properties of diamond [9–15]. In contrast, so far a lot of research works have focused on the presence and bonding form of hydrogen in the diamond lattice and few reports can be found about the effect of hydrogen impurity on the growth process of high temperature high pressure synthesis diamond. Chrenko et al. ﬁrst noted the presence of sharp absorption peaks at 3107 cm -1 and 1405 cm -1 in the infrared spectra of natural diamond and reported that these peaks corresponded to a carbon–hydrogen bond stretching mode [1]. Kiﬂawi et al. also found the 3107 cm -1 peak in HPHT grown after annealing at temperatures above 2100 °C [16]. Yu Borzdov et al. reported the 3107 cm -1 peak in the Fe 3 N–C and predicted the possibility of correlated incorporation of nitrogen and hydrogen during diamond growth [17]. Li et al. reported that hy- drogen atoms incorporated to the diamond lattice as \CH 2 \ symmetric and antisymmetric vibration modes (2850 cm -1 , 2920 cm -1 ) in the hydrogen-doped single diamond crystals [8]. From the surface structure point of view, the C\H bonds stabilize the diamond structure in the growth ambient and prevent transition to other phases such as graphite [18–20]. In natural and synthetic diamonds, the hydrogen atoms enter the lattice structure under a high pressure environment. However, the hydrogen atoms are captured in the low pressure conditions for CVD diamonds. Moreover, no direct experimental work has been performed to study how hydrogen impurity inﬂuences the crystallization in HPHT diamonds during the growth process and provide experimental evi- dences for clarifying the diamond growth mechanism upon hydrogen doping. Thus, more attention should be paid on the study of the inﬂuence of hydrogen impurity in the catalyst and graphite on diamond crystalli- zation process. In the present work, we investigate in detail diamond crystallization using iron–nickel powder as catalyst with TiH 2 additive over a range of temperature from 1250 to 1600 °C and pressures from 5.2 to 6.1 GPa. The diamond spontaneous nucleation and growth were obtained by ﬁlm growth methods (FGM). The synthesized diamonds were charac- terized by optical, scanning electron microscopy (SEM), powder X-ray diffraction (XRD), infrared (IR) absorption and Raman spectra. Our work attempts to clarify the effect of hydrogen on the diamond crystal- lization process. 2. Experimental Diamond crystals are synthesized in a cubic anvil high-pressure and high-temperature apparatus (SPD-6×1200) with a sample chamber of 13 mm edge length at temperatures of 1250–1600 °C and pressures of 5.2–6.1 GPa for 15 min. The sample assembly for diamond synthesis is Int. Journal of Refractory Metals and Hard Materials 38 (2013) 111–117 ⁎ Corresponding author. Tel./fax: +86 431 85168858. E-mail address: maha@jlu.edu.cn (H.A. Ma). 0263-4368/$ – see front matter © 2013 Published by Elsevier Ltd. http://dx.doi.org/10.1016/j.ijrmhm.2013.01.009 Contents lists available at SciVerse ScienceDirect Int. Journal of Refractory Metals and Hard Materials journal homepage: www.elsevier.com/locate/IJRMHM