The surface chemistry of single crystal barium titanate (BaTiO3) has been studied using temperature programmed desorption (TPD). TPD measurements were performed with several probe molecules, including methanol and carbon dioxide. The role of oxygen vacancies in the adsorption and reaction of these molecules was examined by annealing the crystal under oxidizing or reducing conditions prior to performing TPD. It is shown that the adsorption and reaction of methanol and carbon dioxide is enhanced on BaTiO3(001) by annealing the crystal under reducing conditions.
1) Methanol TPD measurements
Methanol desorbs molecularly and also decomposes to form formaldehyde, water, and carbon monoxide. 3 TPD measurements are shown here, corresponding to oxygen-annealed (O1 and O2) and vacuum-annealed (V) surfaces. The desorption spectra of each species are plotted separately. The intensities of the desorption signals are greatest for the vacuum-annealed surface, indicating that oxygen vacancy defects are the active sites for methanol adsorption and reaction on BaTiO3(001) at room temperature.
2) Carbon dioxide TPD measurements
CO2 desorbs molecularly, producing two peaks at 360 K and 720 K. The intensity of the high temperature peak is significantly greater on the vacuum-annealed surface (V) as compared with the oxygen-annealed surface (O2). The high temperature desorption state corresponds to CO2 adsorbed at oxygen vacancy sites, and the low temperature state may correspond to adsorption at step edges or oxygen surface sites.