Observation of an apparent first-order glass transition in ultrafragile Pt–Cu–P bulk metallic glasses
Observation of an apparent first-order glass transition in ultrafragile Pt–Cu–P bulk metallic glasses
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DOI：
10.1073/pnas.1916371117
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发表时间：
2020-01
期刊：
影响因子：
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通讯作者：
J. Na;Sydney L. Corona;A. Hoff;W. Johnson
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文献类型：
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作者：
J. Na;Sydney L. Corona;A. Hoff;W. Johnson
意义玻璃化转变在材料中普遍存在，通常的特征是随着温度的降低，液体中原子或分子重排的动力学停止。潜在的热力学相变的可能存在一直是一个持续争论的主题。在这里，我们提出了令人信服的证据，证明在极高脆性的金属非晶形成液体的极限下，玻璃转变演变为一级熔化转变。这些富铂玻璃以不连续的方式熔化，类似于晶体的熔化。本文报道了一系列近共晶Pt80-xCuxP20大块金属非晶形成合金的构型热力学实验研究。过冷液态合金表现出非常高的脆性，这种脆性随着x的减小而增加，导致玻璃化转变越来越尖锐。随着x的减小，外推的液体考兹曼温度Tk与传统定义的玻璃化转变温度Tg变得难以区分。对于x<；17，观察到的液体构型热与T的关系显示，在明确定义的冻结温度Tgm下，有明显的不连续下降或潜热。这一一级液体/玻璃化转变的熵降约为晶化共晶合金熔化熵的三分之二。在TGm以下，冷冻玻璃的构型熵继续快速下降，在低T极限下接近晶化共晶固体的构型熵。避免了所谓的Kauzmann悖论，液体熵为负(相对于结晶态)，液体构型熵似乎符合热力学第三定律。尽管它们具有超脆性，但x=14和16的液体是块状玻璃成形器，在薄壁二氧化硅管中进行水淬火时，可产生直径高达2 mm和3 mm的完全玻璃棒。低铜含量的合金是玻璃一级熔化的典型例子。
Significance The glass transition is ubiquitous among materials and is commonly characterized by the rapid kinetic arrest of atomic or molecular rearrangements in a liquid as temperature is lowered. The possible existence of an underlying thermodynamic phase transition has been a subject of continuing debate. Here, we present compelling evidence that the glass transition evolves into a first-order melting transition in the limit of very high-fragility metallic glass-forming liquids. These Pt-rich glasses melt in a discontinuous manner similar to melting of a crystal. An experimental study of the configurational thermodynamics for a series of near-eutectic Pt80-xCuxP20 bulk metallic glass-forming alloys is reported where 14 < x < 27. The undercooled liquid alloys exhibit very high fragility that increases as x decreases, resulting in an increasingly sharp glass transition. With decreasing x, the extrapolated Kauzmann temperature of the liquid, TK, becomes indistinguishable from the conventionally defined glass transition temperature, Tg. For x < 17, the observed liquid configurational enthalpy vs. T displays a marked discontinuous drop or latent heat at a well-defined freezing temperature, Tgm. The entropy drop for this first-order liquid/glass transition is approximately two-thirds of the entropy of fusion of the crystallized eutectic alloy. Below Tgm, the configurational entropy of the frozen glass continues to fall rapidly, approaching that of the crystallized eutectic solid in the low T limit. The so-called Kauzmann paradox, with negative liquid entropy (vs. the crystalline state), is averted and the liquid configurational entropy appears to comply with the third law of thermodynamics. Despite their ultrafragile character, the liquids at x = 14 and 16 are bulk glass formers, yielding fully glassy rods up to 2- and 3-mm diameter on water quenching in thin-wall silica tubes. The low Cu content alloys are definitive examples of glasses that exhibit first-order melting.