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The crystal structure of LiAlSi 2 O 6 -II (“β spodumene”)

1968; De Gruyter; Volume: 126; Issue: 1-3 Linguagem: Inglês

10.1524/zkri.1968.126.1-3.46

2366-1798

Chi-Tang Li, Donald R. Peacor,

Nuclear materials and radiation effects

LiAlSi2O6-II ("β spodumene") was found to be tetragonal, space group P43212 (or P41212), a = 7.541 ± 0.001, c = 9.156 ± 0.002 Å, Z = 4, Do = 2.365 and Dc = 2.374 g/cm3. The bond lengths were determined with an accuracy of 0.006 Å for (Si,Al)–O bonds and 0.041 Å for Li–O bonds. The final R value was 6.2%. The structure consists of a three-dimensional aluminosilicate framework. The framework was confirmed to be isotypic with keatite. The Li atoms were found to be coordinated to four oxygen atoms. The distribution of Si and Al in the tetrahedra is random. The structure is dominated by interlocking 5-membered rings of (Si,Al) tetrahedra. All the five-membered rings run approximately parallel to either (010) or (100), and thus help to create zeolite-like channels. These channels account for the ion-exchange properties of LiAlSi2O6-II. Lithium atoms are stuffed in interstitial positions but occupy a general eight-fold site. The four lithium atoms per unit cell are distributed among four sets of paired sites of the eight-fold positions. An explanation for the unusually low thermal expansion behavior of LiAlSi2O6-II is given.