• journal_title：American Mineralogist
• Contributor：Silvia Ori ; Edoardo Mazzucato ; Giovanna Vezzalini
• Publisher：Mineralogical Society of America
• Date：2009-
• Format：text/html
• Language：en
• Identifier：10.2138/am.2009.2914
• journal_abbrev：American Mineralogist
• issn：0003-004X
• volume：94
• issue：1
• firstpage：64
• section：Articles

The thermally induced structural modifications of the natural zeolite barrerite [Na₁₆Al₁₆Si₅₆O₁₄₄·52H₂O, a = 13.6239(4) Å, b = 18.2033(5) Å, c = 17.8317(7) Å, V = 4422.3(3) ų, space group Amma, framework type STI] were studied in a temperature-resolved X-ray powder diffraction experiment, using synchrotron radiation, in the temperature range 339–973 K. In the initial stage of heating, up to 508 K, barrerite Phase A (space group Amma) is stable, the unit-cell volume decreases by about 4% and a water release of about 66% is observed. Between 521 and 598 K, a phase transition to the collapsed so-called barrerite Phase B (space group Amma) is observed. During the transition, the rotation of the 4²5⁴ secondary building units causes a large decrease in cell volume and deformation of the channel system. Phase B, at 611 K, shows the statistical breaking of T-O-T bridges in the 4-rings and the migration of the involved tetrahedral atoms to new “face-sharing” tetrahedra, with a consequent reduction of the free volume of the channels parallel to [100]. The new structure is stable up to 741 K and the total volume decrease is about 16%. A new phase appears from 754 K with cell parameters similar to those reported for the highly deformed barrerite Phase D and is stable up to 910 K, which is the temperature at which the total volume decrease is 22.5%. The material does not undergo amorphization up to the highest temperature investigated.