Abstract The monophasic natrophilite form of NaMnPO4 was synthesized using a simple and scalable one-step hydrothermal method. The heat treatment of the natrophilite NaMnPO4 in the air resulted in the formation of the high-temperature maricite polymorph of NaMnPO4. The crystal structures of these two polymorphs were confirmed by the Rietveld refinements and Raman spectroscopy. The DSC study of the natrophilite form shows a broad exothermic peak indicative of a second-order phase transition to high-temperature maricite form. The band gaps (Eg) of 5.18(2) and 1.88(2) eV were estimated for natrophilite and maricite forms, respectively, by the UV–vis absorption studies. Magnetic studies on polycrystalline natrophilite NaMnPO4 show a complex temperature dependence of magnetic susceptibility, which could be attributed to a canted antiferromagnetic behavior with the Neel’s temperature (TN) of 31 K and an anomaly temperature (T*) of 29 K. Maricite NaMnPO4 also show antiferromagnetic interaction of Mn2+ spins with TN of 18 K.

中文翻译：

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NaMnPO4 的两种多晶型物的合成、晶体结构、光学、拉曼光谱和磁性

摘要 使用简单且可扩展的一步水热法合成了 NaMnPO4 的单相 natrophilite 形式。钠沸石 NaMnPO4 在空气中的热处理导致 NaMnPO4 高温水镁石多晶型物的形成。这两种多晶型物的晶体结构由 Rietveld 精修和拉曼光谱证实。对钠沸石形式的 DSC 研究显示了一个宽的放热峰，表明二级相转变为高温海镁石形式。通过紫外-可见吸收研究，分别估计了 natrophilite 和 maricite 形式的带隙 (Eg) 为 5.18(2) 和 1.88(2) eV。对多晶钠锰矿 NaMnPO4 的磁学研究表明，磁化率具有复杂的温度依赖性，