High-temperature behavior of Sr-doped layered cobaltites Y(Ba(1-x)Sr(x))Co2O5.5: phase stability and structural properties.

In this paper we present a neutron diffraction in situ study of the thermal evolution and high-temperature structure of layered cobaltites Y (Ba, Sr)Co(2)O(5 + δ). Neutron thermodiffractograms and magnetic susceptibility measurements are reported in the temperature range 20 K ≤ T ≤ 570 K, as well as high-resolution neutron diffraction experiments at selected temperatures. Starting from the as-synthesized samples with δ≈0.5, we show that the room temperature phases remain stable up to 550 K, where they start losing oxygen and transform to a vacancy-disordered structure with tetragonal symmetry. Our results also show how the so-called '122' structure can be stabilized at high temperature (around 450 K) in a sample in which the addition of Sr at the Ba site had suppressed its formation. In addition, we present the structural and magnetic properties of the resulting samples with a new oxygen content δ≈0.25 in the temperature range 20 K ≤ T ≤ 300 K.