Hydrothermal Single Crystal Growth and Structural Investigation of the Nepheline and Kalsilite Stuffed Tridymite Species
作者:Rylan J. Terry、Colin D. McMillen、Joseph W. Kolis
DOI:10.1007/s10870-022-00940-6
日期:2023.3
A series of high-quality single crystals of the formula NaxK1−xAlSiO4 were synthesized using a high temperature hydrothermal method. This enabled the detailed single crystal study of four examples of this class of compounds, namely KAlSiO4, Na0.10K0.90AlSiO4 Na3KAl4Si4O16 and NaAlSiO4. The potassium-containing species all had fully ordered AlO4 and SiO4 tetrahedral sites that led to formation of polar acentric structures. In contrast NaAlSiO4 displayed the unusual feature of an exceptionally large and complex unit cell along with complete disordering of the Al and Si sites. This led to the formation of a centrosymmetric structure, that is also a new polymorph of the NaAlSiO4 composition. The polymorphism of hydrothermal KAlSiO4 was also examined in light of the crystal’s synthetic and thermal histories. The study also revealed a structural sensitivity toward the degree of Na/K substitution in the lattice. The strong tendency to form polar acentric structures makes understanding these structures of great interest. These detailed structures resolved a considerable degree of previous structural ambiguity within this nominally simple class of compounds. Structural subtleties are examined in the nepheline–kalsilite series of NaxK1−xAlSiO4, revealing changes in the resulting structure according to synthetic method, thermal history, and alkali metal substitution.
我们使用高温水热法合成了一系列高质量单晶体,其化学式为NaxK1−xAlSiO4。这使我们能够对这类化合物的四个实例进行详细的单晶体研究,即KAlSiO4、Na0.10K0.90AlSiO4、Na3KAl4Si4O16和NaAlSiO4。含钾的物质都具有完全有序的AlO4和SiO4四面体位点,从而形成极性无中心结构。相比之下,NaAlSiO4表现出异常大的复杂晶胞以及Al和Si位点完全无序的异常特征。这导致形成中心对称结构,这也是NaAlSiO4成分的一种新多晶型。我们还根据晶体的合成和热历史研究了水热KAlSiO4的多晶型性。研究还揭示了晶格中Na/K取代程度的结构敏感性。极性无中心结构的强烈倾向使得理解这些结构变得非常有趣。这些详细的结构解决了之前这一类看似简单的化合物中存在的结构模糊性问题。通过对NaxK1−xAlSiO4的霞石-钾长石系列结构微妙性的研究,揭示了合成方法、热历史和碱金属取代对所得结构的影响。