Crystal structure of InTi0.75Fe0.25O3.375 and phase relations in the pseudobinary system InFeO3-In2Ti2O7 at 1300 degrees C

An average structure of incommensurately modulated monoclinic InTi0.75Fe0.2 5O3.375 was determined using single-crystal X-ray diffraction. Unit cell pa rameters are a = 5.9207(8), b = 3.4249(5), c = 6.3836(9), and beta = 107.96 (1) with Z = 2, and the space group is C2/m. The structure with pseudorhomb ohedral symmetry involves two metal positions: M1, practically occupied by In, and M2, by Ti and Fe. Two layers are alternately stacked along the c ax is; one is an edge-shared M1O(6) octahedral sheet and another consists of b ipyramidal. coordination at M2 sites. In the bipyramidal layer, a honeycomb lattice 68% occupied by oxygen ions surrounds the M2 site. These oxygen io ns are subsequently displaced from their original positions to reduce mutua l repulsion. This explains large displacement parameters U-11 and U-22 desp ite the normal U-33 at the M2 site as well as at the oxygen site. Solid sol ution for the present phase is limited to InFeO3:In2Ti2O7 = 2:3 at 1300 deg rees C according to a phase relations study in the pseudobinary system InFe O3-In2Ti2O7. We propose a hypothetical compound with an unusual ABO(3) stru cture based on a comparison of this compound and related structures.