Stabilization of 6H-Hexagonal SrMnO3 Polymorph by Al2O3 insertion

We demonstrate the structural evolution of polymorphic phases in Al2O3-inserted SrMnO3 ceramics synthesized by solid state reaction. While the 4H-hexagonal phase is predominant in pure SrMnO3 ceramics, a small amount of 6H-hexagonal polymorph is identified in addition to the primary 4H-hexagonal SrMnO3 and the secondary hexagonal SrAl2O4 phases in the as-sintered ceramics, evidenced by x-ray diffraction and subsequent Rietveld refinement analyses. The existence of the 6H-hexagonal SrMnO3 phase is corroborated using Raman spectroscopy. The chemical compositions and electronic structures of the Al2O3-inserted SrMnO3 compounds are also examined using energy dispersive spectroscopy and x-ray photoelectron spectroscopy, respectively. The firstprinciples 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 SrMnO3.

Automated summary

This study investigates the structural evolution of polymorphic phases in Al2O3-inserted SrMnO3 ceramics, identifying the presence of the 6H-hexagonal SrMnO3 phase and examining the chemical compositions and electronic structures of the compounds. First-principles calculations show no clear difference in total energies between the 4H- and 6H-hexagonal polymorphs, regardless of the presence of Sr and oxygen vacancies. Possible origins are discussed based on refined lattice parameters of the 6H SrMnO3 phase.