Checkerboard to Stripe Charge Ordering Transition in TbBaFe2O5
  A combined neutron and x-ray diffraction study of TbBaFe2O5 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 TV = 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 TV < T < T* = 308 K. The checkerboard ordering is stabilized by inter-site coulomb interactions which give way to a stripe state stabilized by orbital ordering. 
D. K. Pratt, S. Chang, W. Tain, A. A. Taskin, Yoichi Ando, J. L.   Zarestky, A. Kreyssig, A. I. Goldman and R. J. McQueeney
cond-mat.str-el