Abstract The heat capacity of di-, tri- and tetramethylammonium lead iodide perovskites of general formula (CH3)xNH4–xPbI3 (where 2≤x≤4) has been determined by differential scanning calorimetry (DSC) in the temperature range 289–473 K using the step-scan mode. Standard molar values C0p(298 K) of di-, tri- and tetramethylammonium lead iodide perovskites were found to be: (285.2, 318.8 and 363.4) J K–1 mol–1, respectively. Heat capacity data have been used to evaluate the thermodynamic functions of the three (CH3)xNH4–xPbI3 perovskites (entropy and enthalpy increment). Further DSC experiments were carried out simultaneously with thermogravimetry (TG) at constant heating rate (4 K min–1) to study the thermal behavior. The occurrence of a phase transition was detected in two of the three perovskites in well-defined temperature ranges and the corresponding transition temperatures (taken as the onset temperatures of the DSC peaks) resulted to be 346.6 K and 353.5 K for (CH3)3NHPbI3 and (CH3)4NPbI3, respectively. The three powder samples were also characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses.

中文翻译：

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二、三和四甲基铵碘化铅钙钛矿从 289 到 473 K 的热容量和热力学函数

摘要 通过差示扫描量热法 (DSC) 在 289–473 K 的温度范围内测定了通式 (CH3)xNH4–xPbI3（其中 2≤x≤4）的二、三和四甲基铵碘化铅钙钛矿的热容量使用步进扫描模式。发现二、三和四甲基铵碘化铅钙钛矿的标准摩尔值 C0p(298 K) 分别为：(285.2、318.8 和 363.4) JK–1 mol–1。热容量数据已用于评估三种 (CH3)xNH4–xPbI3 钙钛矿的热力学函数（熵和焓增量）。进一步的 DSC 实验与热重法 (TG) 在恒定加热速率 (4 K min-1) 下同时进行，以研究热行为。在明确定义的温度范围内，在三种钙钛矿中的两种中检测到相变的发生，相应的转变温度（取为 DSC 峰的起始温度）对于 (CH3)3NHPbI3 和 346.6 K 和 353.5 K (CH3)4NPbI3，分别。这三种粉末样品还通过 X 射线衍射 (XRD) 和扫描电子显微镜 (SEM) 分析进行了表征。