Polytype Diversity of the Hydrotalcite-Like Minerals II. Determination of the Polytypes of Experimentally Studied Varieties

Abstract

Almtraet.--Polytype diversity of hydrotalcite-like minerals is mainly a function of the nature of the interlayer anion. Among the varieties with COl-anions, only two-and three-layer polylypes having the same structure as manasseite and hydrotalcite have been confirmed. Stichtite and reevesite, which have been previously identified as six-layer polytypes, are in fact three-layer polytypes.Among SO4 ~ varieties, one-layer and three-layer polytypes have been identified, but the one-layer types are only present in more hydrated minerals with larger interlayer spacings. The three-layer varieties are of three different polytypes, with both P-and O-types ofinterlayers. Both rhombohedral and hexagonal varieties exist. Interlayer type may change during hydration-dehydration or anion exchange. Thus, in contrast with the COs2--bearing minerals, a complete description of the polytype of the SO42--bearing minerals cannot be made by simply indicating the number of the brucite-like layers in the unit cell.The two-layer unit cell seen in refined crystal structures of some minerals with SO42-interlayers is not due to a doubled periodicity of alternation of brucite-like layers but to periodicity of interlayer anions, or layer cations.

Structural Synthon Approach to Predict the Possible Polytypes of Layered Double Hydroxides

“…[11] The sulfate containing minerals have the structures of the 1H, 2H 1 and 3R 1 polytypes. [12] Laboratory-synthesized sulfate LDHs crystallize in the structure of 1H and 3R 1 polytypes depending on the precipitation conditions and exhibit solid-solid interpolytype transformations as a function of temperature and relative humidity. [13,14] In many instances, laboratory-synthesized LDHs crystallize with the incorporation of a very large number of stacking faults, which can indeed be interpreted in terms of the intergrowths of more than one polytypes.…”

Nanocomposite Based Multifunctional Coatings

“…7. Structurally, polytypes based on two-, three-and six-layer polytypes presenting either rhombohedral (2R, 3R, 6R) or hexagonal symmetry (2H, 3H, 6H) are determined from the powder X-ray diffraction diagrams (Bookin et al, 1993). However the LDH and the hybrid derivative materials are usually poorly crystallized and the more common three-layer polytype 3R1 with rhombohedral symmetry (space group R-3m) is often adopted.…”

The crystal structure of stichtite, re-examination of barbertonite, and the nature of polytypism in MgCr hydrotalcites

“…The nature of this polytypism was discussed by Bookin and Drits (1993) and Bookin et al (1993aBookin et al ( , 1993b, with a more recent summary by Evans and Slade (2006). Polytypism in the hydrotalcite structure-type is complex, but arises due to the different possible ways the brucite-like layer can stack (Bookin and Drits 1993;Evans and Slade 2006).…”