萤石结构超离子材料巨机械热效应的预测
Prediction of giant mechanocaloric effects in fluorite-structured superionic materials
摘要：
机械热材料在受到机械应力热作用时会发生温度变化。到目前为止，只有铁电体和超弹性金属合金被认为是潜在的机械热化合物在固态冷却应用中被开发。在这里，我们表明，巨大的机械热效应发生在迄今为止被忽视的快离子导体（FIC），一类多组分材料，其中以上的临界温度，Ts，一个组成离子物种经历了突然增加的流动性。使用第一性原理和分子动力学模拟，我们发现，在萤石结构的FIC，其特征在于由一个大的熵增加的顺序为100 J/K*Kg的超离子过渡，可以外部调谐与流体静力学，双轴或单轴应力。特别地，由于弗伦克尔对缺陷的形成能量的伴随下降，通过施加适度的拉伸应力，Ts可以降低几百度。我们预测，在CaF 2和PbF 2，两个原型萤石结构的FIC，接近其临界点的绝热温度变化分别为100和10 K的顺序。这项工作主张，FIC构成一个新的家庭的机械热材料显示出巨大的前景，为未来的固态制冷应用。
英文摘要：
Mechanocaloric materials experience a change in temperature when a mechanical stress is adiabatically applied on them. Thus far, only ferroelectrics and superelastic metallic alloys have been considered as potential mechanocaloric compounds to be exploited in solid-state cooling applications. Here we show that giant mechanocaloric effects occur in hitherto overlooked fast ion conductors (FIC), a class of multicomponent materials in which above a critical temperature, Ts, a constituent ionic species undergoes a sudden increase in mobility. Using first-principles and molecular dynamics simulations, we found that the superionic transition in fluorite-structured FIC, which is characterised by a large entropy increase of the order of 100 J/K*Kg, can be externally tuned with hydrostatic, biaxial or uniaxial stresses. In particular, Ts can be reduced several hundreds of degrees through the application of moderate tensile stresses due to the concomitant drop in the formation energy of Frenkel pair defects. We predict that the adiabatic temperature change in CaF2 and PbF2, two archetypal fluorite-structured FIC, close to their critical points are of the order of 100 and 10 K, respectively. This work advocates that FIC constitute a new family of mechanocaloric materials showing great promise for prospective solid-state refrigeration applications.
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