Behavior of Catapleiite under Heating and Crystal Structure of its High-Temperature Transformation Product, a New Phase Na6Zr3[Si9O27] with Nine-membered Rings of SiO4 Tetrahedra

Abstract

Thermal behavior of catapleiite, ideally Na₂ZrSi₃O₉ ⋅ 2H₂O, has been investigated with the X-ray diffraction, electroconductivity measurements using impedance spectroscopy, dynamic scanning calorimetry, thermal gravimetry, and infrared spectroscopy. The high-temperature transformation product of catapleiite obtained after annealing of catapleiite at 1000°C has been studied. This is a new microporous zirconosilicate, ideally Na₆Zr₃[Si₉O₂₇], representing a new structural type. It is hexagonal, P6₃/mcm, a = 11.5901(9), c = 9.9546(9) Å, V = 1158.05(16) ų. Its crystal structure model has been obtained using single-crystal X-ray diffraction data and refined by the Rietveld method on the basis of the powder X-ray diffraction data (R = 3.87%). The structure is based on the heteropolyhedral framework, which substantially differs from that of catapleiite and is built by nine-member rings Si₉O₂₇ formed by SiO₄ tetrahedra linked with isolated ZrO₆ octahedra. Extraframework Na cations are located in broad channels of the framework and between the tetrahedral Si₉O₂₇ rings.