The layered compound SrFeO2 with an FeO4 square-planar motif exhibits an unprecedented pressure-induced spin state transition (S = 2 to 1), together with an insulator-to-metal (I-M) and an antiferromagnetic-to-ferromagnetic (AFM-FM) transition. In this work, we have studied the pressure effect on the structural, magnetic, and transport properties of the structurally related two-legged spin ladder Sr 3Fe2O5. When pressure was applied, this material first exhibited a structural transition from Immm to Ammm at P s = 30 ± 2 GPa. This transition involves a phase shift of the ladder blocks from (1/2,1/2,1/2) to (0,1/2,1/2), by which a rock-salt type SrO block with a 7-fold coordination around Sr changes into a CsCl-type block with 8-fold coordination, allowing a significant reduction of volume. However, the S = 2 antiferromagnetic state stays the same. Next, a spin state transition from S = 2 to S = 1, along with an AFM-FM transition, was observed at Pc = 34 ± 2 GPa, similar to that of SrFeO2. A sign of an I-M transition was also observed at pressure around Pc. These results suggest a generality of the spin state transition in square planar coordinated S = 2 irons of n-legged ladder series Srn+1FenO 2n+1 (n = 1, 2, 3,...). It appears that the structural transition independently occurs without respect to other transitions. The necessary conditions for a structural transition of this type and possible candidate materials are discussed. © 2011 American Chemical Society.
- Colloid and Surface Chemistry