Phase-transition induced thermochromic behavior of schafarzikites

热致变色材料可用作给定温度的优良光学指示剂。通过这种方式，可以将热致变色相集成到结构部件中，这表明在温度驱动的材料部分或完全失效的情况下由于颜色变化而存在一定的风险。或者，它可以在太空探索中发挥作用，这取决于太阳的相对位置，从而取决于温度，既可以作为热反射材料，也可以作为热吸收材料。为此，计划研究一旦达到临界温度就可以发生颜色变化的材料。热致变色可以通过具有可逆位移相变的材料来实现，如在钙钛矿型结构中发现的，导致在临界温度TC上可逆的颜色变化。此外，不可逆的重建相变或转变导致永久的颜色变化。如有必要，这两个可以合并。在这方面，重要的是要了解颜色变化机制与热梯度和/或导热率。除了相变温度（TC）之外，如果热致变色转变可以仅用一个物理参数来描述将是有利的。因此，我们提出了一个单一的参数，它可以从一个过渡函数。这个过渡函数被分配到两个相关相的热膨胀行为，由德拜-爱因斯坦非谐性（DEA）模型描述的相变。为了实现相变的热致变色，我们提出了莫来石型O 8 Schafarzikite相稳定的立体化学活性孤电子对，和它们的固溶体作为模型系统。该项目旨在实现以下里程碑：（I）通过实验验证并在必要时进一步开发“相变热膨胀”（TEAPT）模型，（II）表征模型系统L2（M1-xM 'x）O 4（L = Pb 2+，M = Pb 4+，Sn 4+，Pt 4+）为了更好地理解相变过程中热致变色的晶体-化学-物理基础，（III）创建至少相关的热致变色氧化物库，并对允许热致变色转变的宽温度范围的环境友好相进行分类。

A thermochromic material can be used as an excellent optical indicator for a given temperature. In this way, a thermochromic phases can be integrated into structural components, indicating a certain risk due to color changes in case of temperature-driven partial or complete failure of materials. Alternatively, it can function, for instance, in space exploration, depending on the relative position of the sun and thus depending on the temperature, as both heat-reflecting and heat-absorbing material. For this purpose, it is planned to investigate materials that can undergo color changes as soon as the critical temperature is reached. Thermochromism can be realized by materials with reversible displacive phase transitions as found in schafarzikite-type structures, leading to reversible color changes over a critical temperature TC. In addition, irreversible reconstructive phase transitions or transformations lead to permanent color changes. If necessary, these two could be combined. In this respect, it is important to understand the color change mechanism with respect to thermal gradient and/or thermal conductivity. Beside the phase-transition temperature (TC), it would be advantageous if the thermochromic transition could be described with only one physical parameter. As such, we propose a single parameter, which can be derived from a transition function. This transition function is assigned to the thermal expansion behavior of the two involved phases, described by the Debye-Einstein-Anharmonicity (DEA) model across the phase transition. To realize thermochromism across phase transitions we propose mullite-type O8 Schafarzikite phases stabilized by stereochemically active lone electron pairs, and their solid solutions as model systems. The project aims at the following milestones: (I) to experimentally validate and, if necessary, to further development the "thermal expansion across phase transition" (TEAPT) model, (II) to characterize the model system L2(M1-xM'x)O4 (L = Pb2+, M = Pb4+, Sn4+, Pt4+) to better understand the crystal-chemico-physical basis of thermochromism across the phase transitions, (III) to create at least the relevant thermochromic oxide library and categorize the environmental-friendly phases that allow a wide temperature range for thermochromic transitions.