Size evolution of the oxygen interstitial nanowires in La2CuO4+ y by thermal treatments and x-ray continuous illumination

Using synchrotron x-ray diffraction as pump and probe, we show how the oxygen interstitials (Oi) become ordered as a function of temperature under x-ray continuous illumination in an optimum doped La2CuO4+y superconductor. The evolution of Oi grain size and phase segregation is shown by thermal treatments, providing a new experimental avenue for tuning quantum size effects in the system through the direct control of the size of the Oi grains. Here we report the ordering of oxygen interstitials, cooling the sample below 350 K and observing the continuous formation of nanowires. We show the hysteresis in the order–disorder transition controlled by x-ray flux in the sample irradiated with continuous illumination. The shape of oxygen interstitial grains as they grow is anisotropic, showing Oi ordering under x-ray illumination in the a–b plane and in the c-axis direction.