Checkerboard to stripe charge ordering transition in TbBaFe ₂O₅

A combined neutron and x-ray diffraction study of TbBaFe₂O ₅ reveals a rare checkerboard to charge ordering transition. TbBaFe₂O₅ is a mixed valent compound where Fe2 ⁺/Fe3⁺ ions are known to arrange into a stripe charge ordered state below T_V=291 K that consists of alternating Fe2 ⁺/Fe3⁺ stripes in the basal plane running along the b direction. Our measurements reveal that the stripe charge ordering is preceded by a checkerboard charge ordered phase between T_V<T<T*= 308 K. The checkerboard ordering is stabilized by intersite Coulomb interactions which give way to a stripe state stabilized by orbital ordering.