[Image above] Screenshot from a video showing the disintegration of a ceramic as it attempts to undergo a tetragonal-to-monoclinic phase transformation. Credit:Gu et al.那自然（cc boy 4.0）
随着假日季节充满了挥杆，我完全了解锻炼常规滑动的容易。不幸的是，对于我们来说，我们需要更多的工作来重新获得假期正常的假期，而是为形状记忆材料重新获得原始形式。
形状记忆材料是可以在外部刺激的影响下恢复其初始形状的材料，例如温度，光，水分，酸度或电力。某些金属合金是确定的第一材料to exhibit the shape memory effect, and researchers have identified a variety of形状记忆聚合物和聚合物复合材料that exhibit the effect as well.
形状记忆效应基于暴露于外部刺激时经历相变的材料。在形状记忆聚合物的情况下，由于聚合物网络的固有弹性，可以通过各种物理装置实现硬相与软相之间的变化。对于形状记忆合金，效果源于具有两个稳定晶体结构的材料：高温有利的奥氏体相和低温 - 优质（和“屈服”）马氏体相。
(Learn more about the phase change process inthis article。)
当形状记忆合金从一个固相到另一个固相的转化时，它们可以体验到与奥氏体相中分离孪生马氏体相的应力过渡层。这种压力会影响合金的逆转转变的能力。
为了改善固体固相转化的可逆性，研究人员试图提高合金的几何相容性。换句话说，它们仔细地调整合金中的晶格参数以降低过渡层中的弹性能量，从而改善合金的可逆变换在两个固相之间的能力。
与合金一样，陶瓷由晶体结构组成，具有不同的稳定固相。合金和陶瓷之间的这种相似性，特别是zirconia-based ceramics那has led to some success in developing shape memory ceramics by applying the same general strategies used for alloys. For example, afew最近的studies通过提高几何相容性改善各种氧化物系统的相变。
Based on these previous successes, an international team of researchers led by the University of Minnesota Twin Cities and Kiel University in Germany recently conducted a systematic search to identify more ceramics that exhibit reversible phase transformations and shape memory behavior based on improving geometric compatibility. However, as they explain in a新文章published in自然,他们偶然发现了一个看似矛盾的服务le instead.
对于他们的学习，研究人员看着陶瓷系统（Zr / HF）o2(YNb)O4.。该系统显示了与批量Zro相同的相变2—a first-order monoclinic-to-tetragonal phase transformation at 1,170°C and a tetragonal-to-cubic transformation at 2,370°C. (Only the first transformation is relevant to this study.)
在调整晶格参数以提高几何兼容性之后，研究人员试图通过其四边形到单斜相变化冷却陶瓷。然而，而不是转化，多晶慢慢地，稳定地在其谷物边界（一个研究人员称为哭泣的过程）甚至爆炸性崩解。
What mechanism could have caused this unexpected result? The researchers suggest the behavior is due to the (Zr/Hf)O2(YNb)O4.具有多个晶格对应关系的系统，即原子在转换期间的多种可能性。
研究人员基于其中一个对应关系调整了晶格参数，这应该使材料更容易进行转型。但是，它似乎在结构中的其他地方引入了菌株，导致崩解。
The researchers then tried modifying the structure based on an equidistance condition, which takes into account multiple correspondences. This time, the ceramic did demonstrate a reversible transformation.
“While these behaviours seem at first to contradict accepted principles, in fact they serve to widen the set of theory-driven tools applicable in the search for reversible transformations in ceramics,” the researchers write. “Our work also highlights the subtle interplay of multiple transformation correspondences.”
The researchers conclude that their work highlights the need for a general theory of compatibility that includes both phase boundaries and grain boundaries, and a full-atomic-resolution experimental study of grain boundaries in transforming ceramics.
The paper, published in自然那is “Exploding and weeping ceramics” (DOI: 10.1038/s41586-021-03975-5).