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首页> 外文期刊>Acta Crystallographica, Section B. Structural Science >Structure, phase transitions and ionic conductivity of K3NdSi6O15 center dot xH(2)O. I. alpha-K3NdSi6O15 center dot 2H(2)O and its polymorphs
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Structure, phase transitions and ionic conductivity of K3NdSi6O15 center dot xH(2)O. I. alpha-K3NdSi6O15 center dot 2H(2)O and its polymorphs

机译：K3NdSi6O15中心点xH（2）O的结构，相变和离子电导率。 I.alpha-K3NdSi6O15中心点2H（2）O及其多晶型物

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Hydrothermally grown crystals of alpha-K3NdSi6O15. 2H(2)O, potassium neodymium silicate, have been studied by single-crystal X-ray methods. The compound crystallizes in space group Pbam, contains four formula units per unit cell and has lattice constants a = 16.008 (2), b = 15.004 (2) and c = 7.2794 (7) Angstrom, giving a calculated density of 2.683 Mg m(-3). Refinement was carried out with 2161 independent structure factors to a residual, R(F), of 0.0528 [wR(F-2) = 0.1562] using anisotropic temperature factors for all atoms other than those associated with water molecules. The structure is based on highly corrugated (Si2O52-)(infinity) layers which can be generated by the condensation of xonotlite-like ribbons, which can, in turn, be generated by the condensation of wollastonite-like chains. The silicate layers are connected by Nd octahedra to form a three-dimensional framework. Potassium ions and water molecules are located in interstitial sites within this framework, in particular, within channels that extend along [001]. Aging of as-grown crystals at room temperature for periods of six months or more results in an ordering phenomenon that causes the length of the c axis to double. In addition, two phase transitions were found to occur upon heating. The high-temperature transformations, investigated by differential scanning calorimetry, thermal gravimetric analysis and high-temperature X-ray diffraction, are reversible, suggesting displacive transformations in which the layers remain intact. Conductivity measurements along all three crystallographic axes showed the conductivity to be greatest along [001] and further suggest that the channels present in the room-temperature structure are preserved at high temperatures so as to serve as pathways for easy ion transport. Ion-exchange experiments revealed that silver can readily be incorporated into the structure. [References: 22]
机译：α-K3NdSi6O15的水热生长晶体。 2H（2）O，硅酸钕钕，已通过单晶X射线方法进行了研究。该化合物在Pbam空间群中结晶，每个晶胞包含四个分子式单位，晶格常数为a = 16.008（2），b = 15.004（2）和c = 7.2794（7）埃，计算出的密度为2.683 Mg m（ -3）。使用各向异性温度因子对除与水分子相关的所有原子之外的所有原子，使用2161个独立的结构因子进行精炼，以使残留R（F）为0.0528 [wR（F-2）= 0.1562]。该结构基于高度波纹化的（Si2O52-）（无穷大）层，该层可以通过硬硅钙石状带的凝结而生成，而硬硅钙石状带的凝结又可以通过硅灰石状链的凝结来产生。硅酸盐层通过Nd八面体连接形成三维框架。钾离子和水分子位于该框架内的间隙位置，特别是沿[001]延伸的通道内。在室温下老化生长的晶体六个月或更长时间会导致有序现象，导致c轴长度加倍。另外，发现加热时发生两个相变。通过差示扫描量热法，热重分析和高温X射线衍射研究的高温转变是可逆的，这表明层间保持完整的位移转变。沿所有三个结晶轴的电导率测量结果显示，电导率沿[001]方向最大，进一步表明，室温结构中存在的通道在高温下得以保留，从而可作为易于离子迁移的途径。离子交换实验表明，银可以很容易地掺入结构中。 [参考：22]

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