Synthesis of Hexagonal Diamond Achieved by Chinese Research Team: Novel Breakthrough in Post-Graphitic Phase Gradient Conversion(PGPC)

DING Yongkang; LIANG Weizhang; SUN Yuan; MA Yin; DENG Xiaoqin; QIU Zhili

doi:10.15964/j.cnki.027jgg.2025.02.001

Volume 27 Issue 2

Mar. 2025

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Article Contents

Abstract

1. 颠覆性创新—后石墨相梯度转化法

2. 性能突破与应用前景

3. 结论与展望

References

Journal of Gems & Gemmology > 2025 > 27(2): 1-5. > DOI: 10.15964/j.cnki.027jgg.2025.02.001

DING Yongkang, LIANG Weizhang, SUN Yuan, MA Yin, DENG Xiaoqin, QIU Zhili. Synthesis of Hexagonal Diamond Achieved by Chinese Research Team: Novel Breakthrough in Post-Graphitic Phase Gradient Conversion(PGPC)[J]. Journal of Gems & Gemmology, 2025, 27(2): 1-5. DOI: 10.15964/j.cnki.027jgg.2025.02.001

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Synthesis of Hexagonal Diamond Achieved by Chinese Research Team: Novel Breakthrough in Post-Graphitic Phase Gradient Conversion(PGPC)

DING Yongkang^{1, 2,},
LIANG Weizhang^{1, 6},
SUN Yuan³,
MA Yin⁴,
DENG Xiaoqin⁵,
QIU Zhili^{1, 3}

1.
School of Earth Science and Engineering, Sun Yat-Sen University, Zhuhai 519080, China
2.
School of Earth Sciences, Zhejiang University, Hangzhou 310013, China
3.
Key Laboratory of Non-ferrous Metal Oxide Electronic Functional Materials and Devices (Guilin University of Technology), Education Department of Guangxi Zhuang Autonomous Region, Guilin 541004, China
4.
National Gems & Jewelry Testing Co., Ltd., Shenzhen 518020, China
5.
Guangdong Academy of Sciences, Guangzhou 510070, China
6.
Hub Wis Jewellery Strategic Creations (Guangzhou) Co., Ltd., Guangzhou 511458, China

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Received Date: February 15, 2025

Graphical Abstract

Abstract

Abstract

Hexagonal Diamond-HD (also known as Lonsdaleite) is a natural mineral found in meteorites that has attracted attention due to its unique structure and properties. Professors Bingbing Liu and Mingguang Yao from Jilin University, and Shengcai Zhu from Sun Yat-sen University, collaborated to innovatively propose the "Post-Graphite Phase Gradient Conversion method (PGPC)". This method enabled the first successful synthesis and preparation of high-purity (>95%) millimeter-sized Hexagonal Diamond-HD bulk, resolving a half-century-long challenge in this field. The Hexagonal Diamond-HD synthesized via the PGPC method exhibits excellent properties, making it highly promising for applications in ultra-precision machining, quantum information, and deep-space exploration. However, the expensive and complex equipment required, coupled with relatively small single-crystal sizes, may pose substantial challenges on the path to industrialization. Looking ahead, if the pressure window can be optimized and CVD epitaxial technology can be developed, the Hexagonal Diamond-HD could be product in large-scale industrially, thereby driving advancements in high-end manufacturing, quantum technology, and other related fields.
- Hexagonal Diamond-HD,
- Post-Graphite Phase Gradient Conversion method (PGPC),
- synthesis and preparation

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六方金刚石(Hexagonal Diamond-HD)，又称朗斯代尔石^[1-2](Lonsdaleite)，是一种特殊的六方晶系金刚石，自1967年在Diablo峡谷陨石中被首次发现以来^[3]，其成因解释与合成方法一直是高压科学和材料学研究领域的核心挑战。

尽管矿物模拟预测其硬度可能超越立方金刚石^[4]，但受限于天然样品的稀缺性(仅存于陨石撞击事件^[5])以及合成技术的瓶颈，六方金刚石的独立结构长期存在争议^[6]。近日，吉林大学、中山大学等团队在《自然-材料》(Nature Materials)杂志上联合发表题为“通过后石墨相加热合成六方金刚石的通用方法”的研究^[7]，首次实现毫米级高纯度六方金刚石可控制备，材料的相关性能测试展现出多项突破。该成果不仅终结了六方金刚石是否为独立相的学术争论^[6]，更为这种超硬材料的制造和应用提供了全新的解决方案。

1. 颠覆性创新—后石墨相梯度转化法

早期研究试图通过“静态高压法”^[8-11]或模拟陨石撞击的“冲击压缩法(爆炸法)”^[12-13]合成六方金刚石，但最终产物始终与立方金刚石混合，六方金刚石产率较低，且难以分离纯化。甚至曾有研究者认为六方金刚石是立方金刚石的堆垛层错或孪晶，进而质疑六方金刚石是否为独立存在的碳的分子结构。分子动力学模拟表明，石墨向立方金刚石转化的能垒(~0.3 eV/atom)低于六方金刚石(~0.5 eV/atom)，显示立方金刚石为金刚石合成的热力学主导产物^[14]。这一结论与多数实验结果一致，但也暗示若突破动力学限制，高纯六方金刚石或可定向合成。

“后石墨相梯度转化法”(Post-Graphite Phase Gradient Conversion, PGPC)为达成这一重要突破提供了路径(与其他两种合成方法的对比见表 1)。研究团队首先将石墨在超高压(50 GPa)下压缩，使其形成一种中间态—“后石墨相”。这种特殊的后石墨相的层间碳原子通过弯曲和键合锁定(石墨层间形成sp³键，AB堆垛被固定)，阻止了石墨烯层的滑动(抑制了高温下向ABC堆垛的滑动)^[15-18]。此时，对后石墨相进行激光局部加热(1 800 K)，并在高压腔体内设计轴向温度梯度(ΔT ≈ 500 K/mm)，可定向诱导六方金刚石成核生长(碳原子沿六方密排方向有序迁移)。中国的研究团队通过工艺优化，创新性利用大腔体压机(LVP)成功合成了直径2 mm的块状高纯(纯度>95%)、高取向六方金刚石。

Table 1. Comparative analysis of three synthetic methods for hexagonal diamond

对比维度	冲击压缩法(爆炸法)^{[12, 14]}	传统静态高压法^[8-9]	后石墨相梯度转化法(PGPC法)^[7]
合成压力与温度	瞬时高压(~50~100 GPa)，超高温(>3 000 K)	高压(10~25 GPa)，高温(1 000~2 500 ℃)	超高压(30~50 GPa)，中高温(1 400~1 800 ℃)
产物纯度	< 10%(主要产物为立方金刚石和石墨)	30%~50%(与立方金刚石混合)	>95%(几乎纯相六方金刚石)
样品尺寸	纳米级(< 500 nm)	微米级(< 100 μm)	毫米级(~2 mm块体)
结构缺陷	高密度堆垛层错、孪晶和空位	中等密度层错和立方金刚石孪晶	低缺陷(层间取向误差 < 2°)
实验可控性	极低(瞬时过程难调控)	中等(温压可调，但路径不可控)	高(温度梯度定向诱导成核)
设备成本	极高(需爆炸装置或高速飞片)	高(依赖大腔体压机或DAC)	中等(优化后LVP设备可重复使用)
应用潜力	科研(模拟陨石撞击)	材料性能的实验室研究	工业化生成和应用(超硬工具、量子器件)

| Show Table

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新的研究成果首次通过实验揭示了石墨向六方金刚石转化的微观机制：超高压形成的后石墨相“锁住”石墨层间滑动，温度梯度则引导六方金刚石定向生长。这一发现修正了传统理论认为立方金刚石因能垒更低而占主导的认识，并证明通过路径设计可突破热力学限制(使六方金刚石成核能垒降低40%)，实现六方金刚石的高效合成(图 1)^[7]。

Figure 1. Hexagonal diamond synthesized via PGPC method and corresponding SAED patterns (images courtesy of the authors from Reference[7])

DownLoad: Full-Size Img PowerPoint

2. 性能突破与应用前景

与传统方法相比，PGPC法合成的六方金刚石展现出多项性能突破，其中有三项非常突出: (1)超高的硬度。这种材料由六方金刚石纳米层堆叠而成，每层厚度为数十纳米，结构高度有序，轴向和径向维氏硬度分别达到155 GPa和124 GPa，相较于天然金刚石(~110 GPa)提升40%，并且其径向硬度可通过层状结构设计调控^[19]，有望成为已知最硬合成材料; (2)高热稳定性。该材料在1 100 ℃以下无结构变化，到1 200 ℃才开始出现石墨化，优于纳米金刚石900的热稳定性极限^[20]; (3)毫米级规格。PGPC法六方金刚石突破既往纳米尺度^[21]的合成限制，且方法兼容块状石墨、纳米石墨等多种前驱体，为规模化生产铺平了道路。

PGPC法合成的六方金刚石实现了合成纯度和成品规格的突破，有望从实验室走向产业应用。以下设想六方金刚石未来可能的工业应用。在超精密加工工具方面，六方金刚石刀具可显著延长切削寿命，尤其在加工高硬度合金(如钛合金)时优势显著^[9]。同时，六方金刚石在量子信息载体方面也具有较好潜力，六方金刚石中氮-空位(NV)中心的对称性可能优于立方金刚石^[22]，可以为高保真量子比特设计提供新平台。最后，在深空探测防护方面，六方金刚石具有较强的高温热稳定性以及高热导率，结合抗辐射性和超高硬度，也适合作为航天器热屏蔽层材料^[23]。

3. 结论与展望

中国吉林大学刘冰冰教授、姚明光教授联合中山大学朱升财教授的研究团队通过创新性的“后石墨相梯度转化法(PGPC)”，首次实现了高纯度、毫米级六方金刚石的可控制备，解决了该领域长达半世纪的核心难题^[7]。结合理论模拟与实验验证，不仅明确了六方金刚石的独立结构，更为超硬材料的设计制备提供了全新范式。然而，PGPC法仍需克服两大挑战：一是成本与规模化，当前合成方法依赖大腔体压机(LVP)，设备造价高昂；二是单晶尺寸限制，毫米级六方金刚石块体虽属突破，但离晶圆级应用仍有差距。未来，如果可优化压力窗口(如亚稳态合成路径)及开发CVD外延技术，六方金刚石有望从实验室制备走向产业化生产，进而推动高端制造、量子科技等领域的跨越式发展。

就目前而言，学术界及产业界对该材料更多聚焦于高科技超硬材料的生产及应用，相比之下，在珠宝的产业界尚无实际应用的可能。但是，我们仍需关注前沿合成技术的发展，如果该合成制备技术能在未来进一步突破、可产生具有高性价比的高品质单晶体，则有可能产生新的“超级钻石”宝石，为珠宝产业增添新的成员。

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Synthesis of Hexagonal Diamond Achieved by Chinese Research Team: Novel Breakthrough in Post-Graphitic Phase Gradient Conversion(PGPC)