78.
We demonstrate the structural evolution of polymorphic phases in Al
2O
3-inserted SrMnO
3 ceramics synthesized by solid state reaction. While the 4H-hexagonal phase is predominant in pure SrMnO
3 ceramics, a small amount of 6H-hexagonal polymorph is identified in addition to the primary 4H-hexagonal SrMnO
3 and the secondary hexagonal SrAl
2O
4 phases in the as-sintered ceramics, evidenced by x-ray diffraction and subsequent Rietveld refinement analyses. The existence of the 6H-hexagonal SrMnO
3 phase is corroborated using Raman spectroscopy. The chemical compositions and electronic structures of the Al
2O
3-inserted SrMnO
3 compounds are also examined using energy dispersive spectroscopy and x-ray photoelectron spectroscopy, respectively. The first-principles calculations reveal that there is no clear difference between the total energies of 4H- and 6H-hexagonal polymorphs regardless of the presence/absence of Sr and oxygen vacancies. Possible origins are discussed with the estimation of actual strain based on the refined lattice parameter of 6H SrMnO
3.
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