Abstract
We performed, to the best of our knowledge, the world’s first first-principles calculations for the WO2-terminated cubic WO3 (001) surface and analyzed the systematic trends in the WO3, SrTiO3, BaTiO3, PbTiO3 and CaTiO3 (001) surface ab initio calculations. According to our first principles calculations, all WO2 or TiO2-terminated WO3, SrTiO3, BaTiO3, PbTiO3 and CaZrO3 (001) surface upper-layer atoms relax inwards towards the crystal bulk, while all second-layer atoms relax upwards. The only two exceptions are outward relaxations of first layer WO2 and TiO2-terminated WO3 and PbTiO3 (001) surface O atoms. The WO2 or TiO2-terminated WO3, SrTiO3, BaTiO3, PbTiO3 and CaTiO3 (001) surface-band gaps at the Γ–Γ point are smaller than their respective bulk-band gaps. The Ti–O chemical bond populations in the SrTiO3, BaTiO3, PbTiO3 and CaTiO3 bulk are smaller than those near the TiO2-terminated (001) surfaces. Conversely, the W–O chemical bond population in the WO3 bulk is larger than near the WO2-terminated WO3 (001) surface.
Highlights
Throughout the last 20 years the SrTiO3, BaTiO3, PbTiO3 and CaTiO3 (001) surfaces have been broadly explored theoretically and experimentally [1,2,3,4,5,6,7,8,9,10]
The only two exceptions from this systematic trend are the upward relaxation of WO2- or TiO2-terminated WO3 and PbTiO3 (001) surface first-layer O atoms
As a result of our ab initio-calculated atomic relaxation, TiO2-terminated SrTiO3, BaTiO3, PbTiO3 and CaTiO3 (001) surfaces exhibited a reduction of the interlayer distance ∆d12 (−5.80, −5.59, −8.13, −4.46% of a0, respectively) as well as an expansion of ∆d23 (+3.55, +2.51, +5.32, +2.75% of a0, respectively)
Summary
Throughout the last 20 years the SrTiO3, BaTiO3, PbTiO3 and CaTiO3 (001) surfaces have been broadly explored theoretically and experimentally [1,2,3,4,5,6,7,8,9,10]. The SrTiO3, BaTiO3, PbTiO3 and CaTiO3 perovskite cubic unit cells contain five atoms. The only striking difference between the SrTiO3, BaTiO3, PbTiO3 and CaTiO3 cubic perovskites as well as WO3 in its cubic perovskite-like structure is that WO3 has an empty A cation position. We compared our WO2-terminated WO3 (001) surface-atomic and electronic-structure ab initio calculations with our results for the related structure TiO2-terminated SrTiO3, BaTiO3, PbTiO3 and CaTiO3 cubic perovskite (001) surfaces. CaTiO3 (001) surfaces were summarized and analysed in a way readable for a broad audience of scientists
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