PDF《高温高压下碳 的状态方 程及》

第11卷第4期高压物理学报vd.

11,No.4 1997年12月CHINEsE JOURNAL OF HIGH PREssURE PHYsICs Dec.

997 高温高压下碳的状态方程及 相变理论研究 白 杨向东 a,b 张宏a,b 胡栋a经福谦 a 伍.中 国工程物理研究 院流体物理研究所 ,冲 击波物理与爆 轰物理实验室 ,成都523信箱610003) o. 四川联合大学高温高压与原子分 子科学研究 所 ,成 都610065) 摘要研究了高温高压下三相碳 (石墨、金刚石 、 液相碳 )的状态方 程 ,包 括 高压下石 墨到 金刚石 的固-固相变以及 高温下石 墨和金刚石 的熔解 曲线 . 计算 所得到 的金 刚石熔解 曲线具有 正 的斜率 ,石墨-金 刚石-液 相三相点 为伍00K,14GPa左右.i关键 词状态方程 相变高温 高压 中图法分类 号o353.4 0414.12 0521.2 THEORETICAL sTUDIEs OF EOs AND PHAsE TRANsITIoNs OF CARBON UNDER HIGH PREssURE AND HIGH TEMPERATURE Yang Xiangdonga,b,Zhang lΙ onga,b,Hu]Donga,Jing Fuqiana . (a.L夕3o,饣彦or【yr.rs凡. c乃Ⅳαv召 夕饣 JD勿o″ 夕JJo″ P凡ys犭cs R召 s召夕rc尼,so勿莎尼仞 召sJ r饣'Jj彦 "彦 召or FJ" JJ P凡ys攵sP. O.Bo=523,C凡纟ヵg'″ 610003) (b.勤 s彦 J彦 "彦 召or⒕ 彦o″ JC夕刀 'Mc,J召 c切夕 'sc氵召″c召夕JH哲九‰9mp召,ˉd莎仍 '召 夕刀Jr氵氵 g九P'召ss勿 '叼 ,sjc九 仍夕刀 σ ″犭om UmJ矽纟 " ″y,C尼召 刀gd钐610065) ABsTRACT Equation of state(EOS)of three-phase carbon(graphite,diamond,and hq- uid),including solid-sohd phase transition from奁raphite to diamond under high pressure and melting line of graphite and diamond under high temperature has been studied. The meltingˉ curvq of diamond we obtained has a positive slope,and the graphite-diamond- hquid triple point is about4400K,14GPa. KEY WORDs equation of state,phase transitions,high temperature,h噫hpressure. t 本项 目由中国工程物理研究 院流体物理研究所 冲击 波物理 与爆 轰物理 实验室基金资助 . 1997-0⒊ 24收 到原稿 ,1997-0⒍ 1?收 到修 改稿 . 第 4期 杨 向东等 :高 温高压下碳 的状态方 程及相变理论研究 Although the study of phase diagra∏ 1of carbon has had a long history sihce Rooze- boom developed the first p~T phase diagran at the beginning of this century,many un- certainties have been remaining,such as:(l)for a long tirne it is beheved that the slope of the diamond melting line is negative as shown in F. P. Bundy′ s phase diagram in 1989Ell and S. Prawer′ s in1992E刃,butthe work of M. Togaya et al in1994E3彐sh. ws the opposite experi1nental results. This indicates that the slope of the diamond melting line still remains a qontroversial question. (2) The graphitc meltingˉ curve maximun in the region of4800K'ˇ 5000K,5GPa~6GPa was first disGOvered by F. P.Bundy et al【 妇, which has not been given satisfactory explanation up to now. (3):Γhe studies of the graphite meltingn彐sh. w that the liquid rqsistivity decreases with increasing pressure at pressure between1GPa and10GPa,suggestihg a more:matallic character at higher pres- s ures.In this paper we wⅡ l attempt to answer these questions theoretically. For graphite end diamond,EOS of three termsE5彐is adopted 篇尜 筅揞盯)∶箅1叶We use a rnodified Birch equation for夕乃(7)㈤ p乃(7)=1.5B. E― B乃 `十 (1+2B虍 )叩 7/3― (1+B乃 )矿 /3彐F(叩) For graphite, F(饣)=l (叩>D F(叩)=(叩2+叩ˉ 2)/2 (`(D For diamond, F(叩)=1 Here B. 悠the bulk modulus at p=O and T=0,B尼=0.75(4― B;

),B∶ is the pressure derivathe of the bulk modulus at T=0,叩=7.乃/y,7.屁othe mole vo1ume at p=o,T=o. We integrate夕乃(y)to obtain the OK energy E.(y). The lattice thermal effects can be reasonably approxi】 nated by the Einstein model. The electronic properties are de- scribed by the low temperature form (1) (2) 嘛=告&T2 The thermal pressures and energies are related by {擀}v=羊=∞¨ t here subscript r represents the lattice and the electronic terms,respectively.The lattice Gruneisen Coefficient γ I(V)takes the form h(y)=沙+α. -3)说(5) here沙is the value at infinite compression, γ Ois the value when y:=y. . rΓ he electronic Gruneisen coefficient γ eis assumed to be a c. nstant. Using ss=∫ ∶ E(c・s爿-ct,e)/T彐d7冖,we (3) (4)