Incommensurately modulated crystal structure of flamite - natural analogue of αH′-Ca2SiO4

被引：5

作者：

Rashchenko, Sergey, V ^{[1
,2
]}

Seryotkin, Yurii, V ^{[1
,2
]}

Sokol, Ella, V ^{[1
]}

Kokh, Svetlana N. ^{[1
]}

机构：

[1] Soboley Inst Geol & Mineral SB RAS, 3 Koptyuga Ave, Novosibirsk 630090, Russia

[2] Noyosibirsk State Univ, 1 Pirogova St, Novosibirsk 630090, Russia

来源：

ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS | 2019年 / 75卷

基金：

俄罗斯科学基金会;

关键词：

flamite; calcium orthosilicate; aperiodic structure; incommensurate modulation; combustion metamorphism; SOLID-SOLUTION; DICALCIUM; TEMPERATURE; ROCKS; PHASE; NA;

D O I：

10.1107/S2052520619013623

中图分类号：

O6 [化学];

学科分类号：

0703 ;

摘要：

Crystal structures of unquenchable high-temperature polymorphs of Ca2SiO4, important in cement chemistry, have eluded single-crystal X-ray analysis. However, the problem may be addressed by studying chemically stabilized Ca2SiO4 polymorphs at ambient temperature. Here an incommensurately modulated crystal structure of flamite [Pnma(0 beta 0)00s, q = 0.2728 (2)b*, a = 6.8588 (2) angstrom, b = 5.4301 (2) angstrom, c = 9.4052 (3) angstrom] is described. It is a mineral analogue of orthorhombic alpha(H)'-Ca2SiO4 (stable between 1160 and 1425 degrees 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 (Ca1.75K0.12Na0.12)(1.99)(Si0.74P0.26)(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.

引用

页码：1137 / 1143

页数：7

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