Spontaneous rearrangement of the checkerboard charge order to stripe order in La1.5Sr0.5NiO4

The charge ordering in La1.5Sr0.5NiO4 has been studied using the neutron-diffraction technique. An interesting rearrangement of the charge ordering was observed as a function of temperature. With decreasing temperature, a checkerboard-type charge order is formed below T(CO)(C)similar to480 K. It is, however, taken over by the stripe-type charge order with an incommensurability twice as large as that of the spin order below T(CO)(IC)similar to180 K. Surprisingly, the stripe phase persists up to x=0.7 for highly hole-doped samples of Nd2-xSrxNiO4 with 0.45less than or equal toxless than or equal to0.7.