Computational design and fabrication of novel functional materials based on tin oxide

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Novel gas sensing and p-type conducting properties of tin dioxide (SnO_2) have been explored using a combined theoretical and experimental approach. A computational method to predict the properties under a given gas pressure and temperature has been developed, by combining phonon calculation based on first-principles projector augmented wave method, cluster expansion technique, and Monte Carlo simulation. It is demonstrated that using this approach phase transition behaviors and phase boundaries are well reproduced for binary and ternary oxide systems. Appling to molecule adsorption on SnO_2 surfaces, adsorption energy is shown to significantly depend on surface planes and atomic structures. It also has a strong dependence on ambient atmosphere and temperature. Based on the results, a guideline for the design of surface structures with superb sensing properties is suggested.Calculations have been conducted as well for various dopants in SnO_2 in order to examine its potential p-type conductivity. A heavy doping of impurities having a large size mismatch with Sn results in the formation of impurity-induced bands in the band gap. It is suggested that the conductivity can be altered by controlling the impurity bands. Pulsed laser deposition of doped SnO_2 films has been made on the basis of the theoretical prediction.