Surface reconstruction and band alignment of nonmetallic A(II)B(IV)O3 perovskites
| Autor: | Ha-Jun Sung, Yasuhide Mochizuki, Fumiyasu Oba |
|---|---|
| Rok vydání: | 2020 |
| Předmět: |
Materials science
Physics and Astronomy (miscellaneous) 02 engineering and technology 021001 nanoscience & nanotechnology 01 natural sciences Surface energy Hybrid functional Tetragonal crystal system Crystallography Dipole Ionization Goldschmidt tolerance factor 0103 physical sciences General Materials Science Orthorhombic crystal system 010306 general physics 0210 nano-technology Stoichiometry |
| Zdroj: | Physical Review Materials. 4 |
| ISSN: | 2475-9953 |
| Popis: | Understanding the band alignment at oxide surfaces is of great importance for designing oxide-surface-based electronic, catalytic, and photocatalytic applications. We systematically investigate the band alignment of (001) surfaces of $A(\mathrm{II})B(\mathrm{IV}){\mathrm{O}}_{3}$ perovskites ($A=\mathrm{Ca}$, Sr, Ba, Pb; $B=\mathrm{Ti}$, Zr, Hf, Ge, Sn) through first-principles calculations using semilocal and hybrid functionals. The results are discussed with an emphasis on the effects of surface reconstruction on the band alignment. Reconstructed stoichiometric surfaces are generated by an evolutionary algorithm with surface energy minimization for various surface periodicity units by taking the orthorhombic phase of $\mathrm{CaTi}{\mathrm{O}}_{3}$, the tetragonal phase of $\mathrm{SrTi}{\mathrm{O}}_{3}$, and the cubic phases of $\mathrm{SrTi}{\mathrm{O}}_{3}$ and $\mathrm{BaSn}{\mathrm{O}}_{3}$ as representatives. Two types of reconstruction patterns are obtained as energetically favorable configurations common to these phases, which are composed of half-$A\mathrm{O}$ and -$B{\mathrm{O}}_{2}$ topmost layers, respectively. These reconstructed stoichiometric surfaces have energies comparable to those of nonstoichiometric surfaces, with full $A\mathrm{O}$ or $B{\mathrm{O}}_{2}$ termination under specific chemical potential conditions in $\mathrm{CaTi}{\mathrm{O}}_{3}$ and $\mathrm{SrTi}{\mathrm{O}}_{3}$. We systematically calculate the positions of the valence-band maxima and the conduction-band minima with respect to the vacuum level, namely, the ionization potentials and the electron affinities, for the reconstructed stoichiometric and the nonstoichiometric surfaces of $A(\mathrm{II})B(\mathrm{IV}){\mathrm{O}}_{3}$ perovskites. The ionization potentials and electron affinities at the reconstructed surfaces well describe the termination-plane dependencies of experimentally reported values. The surface band positions are found to show an approximately linear trend against the Goldschmidt tolerance factor, with the sign of slopes opposite to each other for the two types of reconstruction patterns. This tendency is explained by the tolerance-factor dependency of surface rumpling that significantly modifies the surface dipole, although the band positions of $A=\mathrm{Pb}$ systems exhibit a larger deviation from an expected trend due to Pb lone-pair states. |
| Databáze: | OpenAIRE |
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