Thermal anomalies and phase transitions in Pb2Sc2Si2O9 and Pb2In2Si2O9
Thermal anomalies and phase transitions in Pb2Sc2Si2O9 and Pb2In2Si2O9
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DOI：
10.1515/zkri-2021-2046
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发表时间：
2021-10
期刊：
影响因子：
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通讯作者：
M. Gogolin;M. Murshed;L. Bayarjargal;D. Klimm;T. Gesing
中科院分区：
文献类型：
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作者：
M. Gogolin;M. Murshed;L. Bayarjargal;D. Klimm;T. Gesing
摘要 Pb2Sc2Si2O9 和 Pb2In2Si2O9 分别是矿物镍铁长石的含钪和铟的结构类似物，是通过 PbO 助熔剂自发结晶而生长的。相应的多晶粉末样品是通过传统的固态方法合成的。使用温度依赖性单晶和粉末 X 射线衍射、热容测量、二次谐波发生实验和拉曼光谱对这些化合物进行了彻底表征。在环境条件下，两种化合物均在非中心对称 Pna21 空间群中结晶，并在高温下经历相变至中心对称 Pbcn 空间群。 Pbcn 到 Pna21 的相变由与温度相关的二次谐波生成的信号补充。比热容表现出明显的尖点，支持λ型二级相变。一些选择性拉曼模式的温度依赖性进一步补充了这些发现，显示了声子在相变过程中的软化和硬化。
Abstract Pb2Sc2Si2O9 and Pb2In2Si2O9, respectively, the scandium and indium containing structural analogues of the mineral kentrolite are grown by spontaneous crystallization from a PbO flux. The corresponding polycrystalline powder samples are synthesized by conventional solid-state approach. The compounds are thoroughly characterized using temperature-dependent single crystal and powder X-ray diffraction, heat capacity measurements, second harmonic generation experiments and Raman spectroscopy. At ambient conditions, both compounds crystallize in the non-centrosymmetric Pna21 space group and undergo phase transitions to the centrosymmetric Pbcn space group at elevated temperatures. The Pbcn into Pna21 phase transitions are complemented by the signals of the temperature-dependent second harmonic generation. The specific heat capacity exhibits distinct cusp, supporting the λ-type second-order phase transition. The temperature dependency of some selective Raman modes further complements the findings, showing softening and hardening of the phonons across the phase transitions.