In situ X-ray diffraction studies of Pr sub(2-x) NiO sub(4+ delta ) crystal structure relaxation caused by oxygen loss

Fine powders of Pr sub(2-x)NiO sub(4+ delta ) (PNO) oxides (x = 0 / 0.3) synthesized by Pechini route were uniaxially pressed into pellets and sintered at 1300 [degrees]C under air. Chemical diffusion coefficients (D sub(chem).) and surface exchange constants (k sub(chem).) were estimated by analysis of the weight and conductivity relaxations after step-wise change of pO sub(2). In situ XRD studies were carried out in VEPP-3 facilities of the Siberian Center of Synchrotron Radiation using unique high-temperature camera and procedures. Analysis of dynamics of the cell volume expansion caused by oxygen loss with due regard for penetration depth of X-rays into the pellet allowed to estimate D sub(chem) and k sub(chem), found to be close to those obtained by traditional methods. Isolated Pr vacancies appear to be the most important for fast oxygen diffusion and high surface reactivity providing the highest values of k sub(chem), and D sub(chem) for Pr sub(1.9)NiO sub(4+ delta ) composition.