锗dc到β-Sn结构的压致相变动力学研究

Phase Transition Kinetics of Ge from dc Phase to β-Sn Phase under High Pressure

室温常压下锗是一种具有高载流子迁移率和窄带隙的半导体材料。在高压下,锗具有多种与硅相似的晶相,其有趣的高压行为如压致金属化和超导电性转变引起了高压研究领域的广泛关注。然而,其核心的高压相变动力学机制却鲜有深入研究。利用先进同步辐射光源的高通量X射线衍射结构诊断手段,结合基于金刚石压砧的快速动态压缩技术,研究了锗在高压相变过程中的结构演化机理。采用气膜与压电陶瓷相结合的快速加载方法,实现了数十太帕每秒的压缩速率。采用第三代同步辐射高通量粉光X射线衍射技术,实现了数十微秒时间分辨的结构解析。在相变过程中,新旧相中不同晶面的衍射强度变化存在一定的先后顺序,证实了锗的半导体相(金刚石立方结构)到金属相(β-Sn结构)的转变是位移型相变。此外,通过与静态压缩X射线衍射数据的对比,证实了在此相变过程中不同晶面消失/出现存在先后顺序的行为只能通过动态压缩和动态探测手段观察。

Germanium is a semiconductor with good performances of high carrier mobility and narrow band gap at ambient conditions. Under high pressure, it undergoes serials of polymorphs similar to the case of silicon, and the attractive characteristics in its high pressure phases such as metallization and superconducting transition make it one of the most appealing materials in high pressure research. However, its fundamental phase transition kinetics has been rarely studied. In this work, we present our experimental observations on the phase transition of germanium via a novel designed rapid compression tool and ultrafast time-resolved X-ray diffraction(XRD) acquisition system. The compression rate reaches to tens of TPa/s which is realized by combining gas membrane and piezoceramics compression methods in a symmetrical dynamic diamond anvil cell(dDAC). The time-resolved XRD with high resolution in microseconds is achieved by integrating the high flux pink beam diffraction, an X-ray scintillator to convert diffracted X-rays to visible lights and a high-speed optical camera. It is found that there is a time sequence for diffraction planes disappearing and appearing of dc and β-Sn phases, showing a displacive feature for this phase transition. In addition, the XRD evolution under static compression is also given for comparing with the dynamic compression, the results demonstrate our novel designed rapid compression and ultrafast time-resolved XRD setup shows a great potential for studying the high pressure phase transition kinetics.