M. Rokita

Spectroscopic studies of different aluminosilicate structures

Abstract The applicability of the MIR spectroscopy for aluminosilicate structures description of some natural zeolites has been shown in this work. The suitability of the spectra for a “convenient” recognition and identification of the kind of SiO 4 and AlO 4 tetrahedra rings predominating in a given zeolite structure has been described. The interpretation process was supported by the decomposition of the spectra into component bands. The estimation of Si:Al ratio in zeolites and the degree of ordering in the sequence of both building space framework tetrahedra can be done on the basis of parameters (band position and intensity) of the main bands due to Si(Al)–O bond vibrations. The results based on the spectra of zeolites were then compared with the data obtained in the previous works on potassium aluminosilicates (also having framework structures thought not classified as zeolites) and ring silicates (containing isolated silicooxygen rings). Such comparison allows to draw more general conclusions relating to the interpretation of MIR spectra of different silicate structures.

The AIPO4 polymorphs structure in the light of Raman and IR spectroscopy studies

Abstract Raman spectra of low-temperature polymorphic forms of AlPO 4 (berlinite, phosphocristobalite and phosphotridymite) are presented. The interpretation of the spectra has been carried out using the model of [PO 4 ] 3− tetrahedron isolated by Al 3+ cations. The theoretical number of Raman active modes has been determined using the factor group analysis. Raman and IR spectra have been compared regarding adequate selection rules. The crystalline field splitting and Davydov effects have been discussed. It has been shown that AlPO 4 polymorphs, usually classified as a framework structure, because of the similarity to SiO 2 , should be rather treated as an orthophosphate structure. Thus the model of the oxygen bridge, commonly used for interpretation of framework structures, should not be used in the case of AlPO 4 .

Spectroscopic studies of polymorphs of AlPO4 and SiO2

Abstract IR spectra of basic polymorphic forms of AlPO4, measured at different temperatures, are presented. Diffuse reflectance spectroscopy has been used for high temperature measurements. According to the crystal structures of different AlPO4 forms by means of factor group analysis, a number of modes and their activities have been determined. An attempt to assign bands to specific normal vibrational modes has been undertaken, comparing spectra of subsequent forms of AlPO4 with each other. The obtained results have been discussed with regard to data referring to various isomorphous polymorphic forms of SiO2, comparing, respectively, cristobalite with phosphocristobalite, berlinite with quartz, and phosphotridymite with tridymite (M. Handke and W. Mozgawa, Vib. Spectrosc. 5 (1993) 75; M. Handke, W. Mozgawa and M. Rokita, Michrochim. Acta [Suppl] 14 (1997) 511). Differences and similarities have been shown for the spectroscopic data and thus for structures of AlPO4 and SiO2.

Structural studies of the NaCaPO4-SiO2 sol-gel derived materials

Structural studies of the NaCaPO4– SiO2 materials have been carried out. Amorphous materials from this system, after controlled crystallization process, can be used as potential nanomaterials. Structural studies of nanomaterials are of fundamental importance in view their future applications. Materials of different [PO4] 32 /[SiO4] 42 tetrahedra proportion have been prepared. Na þ and Ca 2þ cations have compensated the negative charge of the lattice. Amorphous and crystalline materials have been obtained by sol – gel as well as conventional melting methods. The XRD phase identification has enabled amorphous and crystalline materials identification and suggests the separation of phosphorus and silicate crystalline phases. The obtained materials were examined using the electron scanning microscope and EDX spectrometer. Analysis of electron scanning microscope maps shows considerable inhomogeneity of crystalline samples. Fluctuations in ions distribution, in case of amorphous materials, have been noted too. DTA investigations have enabled to find the probable characteristic temperatures of glass crystallization. Detailed infrared spectroscopy measurements have been carried out. The spectra of obtained materials have been compared with the spectra of cristobalite. Spectroscopic studies confirm the inhomogeneity of materials. q 2003 Elsevier Science B.V. All rights reserved.