Octahedral tilting evolution and phase transition in orthorhombic NaMgF₃ perovskite under pressure

Abstract

Rietveld refinement of monochromatic synchrotron x‐ray powder diffraction data was used to study the evolution of octahedral tilting in the orthorhombic NaMgF3 perovskite under pressure. Hydrostatic pressure conditions were ensured up to 16 GPa using helium as a pressure medium. The tilting angles of MgF6 octahedral framework were observed to increase with increasing pressure. The compression mechanism was observed to be dominated by the shortening of the octahedral Mg‐F bond below 6 GPa, and then controlled by the increase of the octahedral tilting above 12 GPa. The bulk modulus of NaMgF3 was estimated as 76.0 ± 1.1 GPa. A phase transition was observed at about 19.4 GPa in a separate run when silicone oil was used as pressure medium, and this high‐pressure phase could be rationalized in term of a post‐perovskite structural model.

Pressure Induced Octahedral Tilting Distortion in Ba2YTaO6.

“…For example, a recent study of the perovskite NaMgF 3 demonstrated that the compression mechanism was dominated by a shortening of the Mg F bonds below 6 GPa and controlled by an increase in octahedral tilting above 12 GPa; however, in that experiment no change in the type of octahedral tilting was observed. 8 We have obtained similar results in this study of Ba 2 YTaO 6 , where bond compression is the dominant mechanism at lower pressures, while octahedral tilting becomes more important at higher pressures. These results also suggest that the Ba O bonds are more compressible than the Ta O and Y O bonds, which is evident in the onset of the octahedral tilting transition.…”

High pressure structural studies on SrRuO3

“…However, the use of these equations in a semiquantitative manner has been done by many. For example, the angles estimated from the lattice parameters and calculated directly from the atomic positions determined by high resolution diffraction measurements show very good agreement in the orthorhombic perovskite NaMgF 3 [13]. In fact, as one goes from SrRuO 3 to CaRuO 3 , direct calculation of the average Ru-O-Ru bond angle decreases by 14:1 [5], while the estimate from lattice parameters is 15:4 .…”

Two-stages Dissociation of NaMgF3Post-Perovskite: A Potential Low-Pressure Analog of MgSiO3at Multi-Mbar Pressures

“…In order to investigate post-PPV transitions, low-pressure analogs of MgSiO 3 are highly desirable. NaMgF 3 is one of analogs of MgSiO 3 and has been studied both experimentally and theoretically [10][11][12][13][14][15]. It has been confirmed that NaMgF 3 takes the perovskite structure at ambient conditions and transforms into the PPV under pressure.…”