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首页> 外文期刊>Acta Crystallographica, Section B. Structural science, crystal engineering and materials >Incommensurately modulated crystal structure of flamite - natural analogue of α'_H-Ca_2SiO_4
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Incommensurately modulated crystal structure of flamite - natural analogue of α'_H-Ca_2SiO_4

机译：丙位石矿的不计晶体结构 - α''_h-ca_2sio_4的自然类似物

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摘要

Crystal structures of unquenchable high-temperature polymorphs of Ca_2SiO_4, important in cement chemistry, have eluded single-crystal X-ray analysis. However, the problem may be addressed by studying chemically stabilized Ca_2SiO_4 polymorphs at ambient temperature. Here an incommensurately modulated crystal structure of flamite [Pnma(0β0)00s, q = 0.2728 (2)b*, a = 6.8588 (2) ? , b = 5.4301 (2) ? , c = 9.4052 (3) ? ] is described. It is a mineral analogue of orthorhombic α'_H-Ca_2SiO_4 (stable between 1160 and 1425°C), naturally stabilized by substitution with phosphorus. The incommensurate modulation results from wave-like displacement of cation sites accompanied by tilting of (Si,P)O_4 tetrahedra and variation of the Na/(Ca +Na + K) ratio along the modulation period. The studied sample from Hatrurim Basin (Negev Desert, Israel) with composition (Ca_(1.75)K_(0.12)Na_(0.12))_(1.99)(Si_(0.74)P_(0.26))_(1.00)O_4 also demonstrates pseudomerohedral cyclic twinning around the a axis, which results from pseudohexagonal topology of the crystal structure and complicates the indexing of X-ray diffraction data.
机译：CA_2SIO_4未抑制高温多晶型物的晶体结构，在水泥化学中重要，具有耐用的单晶X射线分析。然而，可以通过在环境温度下研究化学稳定的CA_2SIO_4多晶型物来解决问题。这里有一种不计的丙位石晶体结构[PNMA（0β0），q = 0.2728（2）B *，a = 6.8588（2）？ ，b = 5.4301（2）？ ，c = 9.4052（3）？描述了。它是正交α'_H-CA_2SIO_4的矿物质类似物（1160至1425℃之间的稳定，通过磷取代而自然稳定。由阳离子位点的相当的调节结果伴随着（Si，P）O_4 Tetrahedra倾斜和沿调制周期的Na /（Ca + Na + K）比的变化。来自Hatrurim盆地（Negev Desert，以色列）的研究采用组成（CA_（1.75）K_（0.12）NA_（0.12））_（1.99）（SI_（0.74）P_（0.26））_（1.00）O_4也证明了假币形状围绕轴线缠绕循环，这由晶体结构的伪胶质拓扑结果产生并使X射线衍射数据的分度复杂化。

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