Infrared spectroscopic studies on amorphous and crystalline lanthanum aluminoborates

摘要

The development of lanthanum aluminoborate crystalline phase of LaAl2.03B4O10.5 (124) composition from the amorphous xerogels prepared by sol-gel technique has been characterized by thermal analysis and infrared spectroscopy. Thermal analysis evidenced continuous weight losses up to 800degreesC as a result of nitrates decomposition, glycerol combustion and clehydroxylation. The crystallization of amorphous xerogels occurs between 760 and 860degreesC. The IR data indicate that the local structure dramatically modifies as crystalline phases are developed from the amorphous xerogels. The major changes occur in the boron surrounding where, from the most borons which are three-coordinated in amorphous xerogels, almost only tetra-coordinated species appear in the crystalline samples. While in amorphous xerogels, aluminum occurs as hexa-, penta- and tetra-coordinated by oxygen, in the crystalline samples obtained from lanthanum aluminoborates, amorphous precursors of composition corresponding to 124-lanthanum aluminoborate phase aluminum, it is preponderantly penta- and hexa-coordinated. [References: 22]