Relationships between the Structural, Vibrational, and Optical Properties of Microporous Cancrinite

Abstract

The crystal-chemical, vibrational, and optical properties of microporous aluminosilicate cancrinite have been investigated by combining electron probe microanalysis, single-crystal X-ray diffraction, infrared (IR) absorption, Raman, UV-Visible absorption, and electron spin resonance spectroscopy. The behavior of the peaks in the IR spectra was also studied during the dehydration of the sample. The analyzed sample has the following unit cell parameters (P63): a = 12.63189(14) Å, c = 5.13601(7) Å. The empirical formula, based on 12(Si + Al), is Na6.47Ca1.23K0.01[Al5.97Si6.03O24] (CO3)1.45(SO4)0.03Cl0.01·2H2O. The Al-Si framework of AB-type is formed by columns of based-shared “cancrinite” (CAN) cages, containing Na and H2O positions located on the 3-fold axis, and channels with CO3 groups, lying in two mutually exclusive and partially occupied positions in the center of the channel, and split Na/Ca cation sites. The revealed characteristics are somewhat different in comparison with the cancrinite structural features previously described in the literature. Studied crystals change color from grayish-pink to blue after X-ray irradiation (104 Gy). The blue color of the irradiated cancrinite is caused by the formation (CO3)−● radicals in the crystals. Combining the results obtained using the selected methods will provide a better understanding of the relationships between the structural, chemical, and optical-physical properties of microporous aluminosilicates.

Keywords

• cancrinite
• crystal structure
• crystal chemistry
• IR spectroscopy
• Raman spectroscopy
• optical absorption spectroscopy