Chemical Pressure Effect on Structural and Physical Properties of 15R-Srvo2.2n0.6 with Anion-Vacancy Order

We have recently demonstrated the formation of 15R-type SrVO2.2N0.6 with an anion-vacancy order in the [111] direction from the cubic SrVO3 perovskite by topochemical reactions, but in epitaxial thin films the anion-vacancy order pattern changes. In the present study, the effect of partial Sr-site substitution by Ca on the structure and physical properties was investigated. We found that the 15R structure is preserved up to a Ca-substitution of 20%, with nearly isotropic lattice compression (Delta a = -0.52% and Delta c = -0.67%). This result indicates that the switching behavior of the anion-vacancy layers observed in the thin films is due to anisotropic biaxial strain and that the 15R-phase is robust against isotropic chemical pressure. First-principle theoretical calculations support this interpretation, revealing that anion-vacancy plane switching under isotropic pressure in SrVO2.2N0.6 requires >4 GPa corresponding to similar to 1% strain. Magnetization and specific heat measurements of the Ca-substituted samples suggest a possible increase in magnetic fluctuations in the low-temperature regime relative to the pristine SrVO2.2N0.6 with a two-dimensional electronic structure.