ADSORPTION OF CARBON-DIOXIDE BY FERROELECTRIC LITHIUM-NIOBATE
No Thumbnail Available
Date
1995
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Abstract
Desorption curves of CO2 are presented for powder of lithium niobate with main particle sizes of 1000, 500, 200, 100 and 50 mu m in diameter. The percentage of surface area occupied by CO2 molecules is calculated after measuring the total surface area of the samples using N-2 single point BET. Adsorption of CO2 and N-2 were measured with a Quantasorb instrument using flowing helium. The ratio of the surface area covered by CO2 with respect to N-2 changes from 11.5% for the 50 mu m particles down to 6.7% for the 100 mu m particles. Adsorption of CO2 for particles equal to or larger than 200 mu m could not be measured with our technique. XPS results on a single piece of lithium niobate indicated that CO2 is adsorbed on the surface when only Nb3+ ions are present. Induced crystallographic transformation of the crystal by an applied 2.5 kV field changes its surface composition from an initial mixture of Nb5+ and Nb3+ ions to pure Nb5+ ions and as a consequence of this change, adsorbed CO2 was released. A tentative explanation of these results is that the adsorption of the CO2 molecules by the ferroelectric substrate is due to a particular local electrostatic potential created by surface ions, in agreement with Pacchioni's work on other oxide surfaces.
Description
Keywords
CARBON DIOXIDE, CHEMISORPTION, DIELECTRIC PHENOMENA, NIOBIUM, PHOTOEMISSION, POLYCRYSTALLINE SURFACES, SOLID-GAS INTERFACES, THERMAL DESORPTION, THERMAL DESORPTION SPECTROSCOPY, X-RAY PHOTOELECTRON SPECTROSCOPY