Powders of silver (Ag2HgI4) and copper (Cu2HgI4) tetraiodomercurates were synthesized by a simple co-precipitation method. Their phase transition behavior was investigated by differential scanning calorimetry, X-ray diffraction (XRD), as well as diffuse reflectance to determine its reversibility and stability during heating–cooling cycles. Calorimetry showed a sharp transition at 51 °C when heating, and at 40 °C when cooling for Ag2HgI4 samples. For Cu2HgI4 samples in the first cycle, one peak was observed when heating at 69.6 and 49.7 °C when cooling. However, in these samples, the first peak splits into two peaks when heating during the second and third cycles (67.5 and 57.8 °C), indicating a probable loss of crystallinity. XRD and diffuse reflectance showed that the transition starts almost since the beginning of the warming-up process and is more evident around 40 °C for Ag2HgI4 and around 60 °C for Cu2HgI4. The energy bandgap indicates that Ag2HgI4 and Cu2HgI4 behave differently during the transition. Copper tetraiodomercurate follows almost the same path for heating than for cooling. Its reversible thermochromic and superionic properties are promising for several applications and open the possibility of using them as inclusions in smart composite systems.

中文翻译：

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热致变色银和铜四碘汞酸盐 (Ag2, Cu2) HgI4 陶瓷的结构和光学性能研究

通过简单的共沉淀法合成了银 (Ag2HgI4) 和铜 (Cu2HgI4) 四碘汞酸盐粉末。通过差示扫描量热法、X 射线衍射 (XRD) 以及漫反射来研究它们的相变行为，以确定其在加热-冷却循环过程中的可逆性和稳定性。对于 Ag2HgI4 样品，量热法显示加热时在 51°C 和冷却时在 40°C 出现急剧转变。对于第一个循环中的 Cu2HgI4 样品，在 69.6 和 49.7 °C 加热时观察到一个峰。然而，在这些样品中，在第二个和第三个循环（67.5 和 57.8 °C）期间加热时，第一个峰分裂成两个峰，表明结晶度可能会损失。XRD 和漫反射率表明转变几乎从预热过程开始就开始了，并且在 40 °C 左右对于 Ag2HgI4 和对于 Cu2HgI4 来说在 60 °C 左右更为明显。能带隙表明 Ag2HgI4 和 Cu2HgI4 在转变过程中表现不同。四碘汞酸铜的加热路径与冷却路径几乎相同。其可逆的热致变色和超离子特性有望用于多种应用，并开启了将它们用作智能复合系统中的夹杂物的可能性。