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The ubiquitous oxygen vacancies and related defects are well known to be the culprits for various properties of perovskite oxides.One of the most interesting issues is that the vacancies possess an inherent inhomogeneous distribution leading to self-ordering in these materials.This phenomenon known as phase separation or stripe phase has attracted considerable interest in high temperature superconducting cuprates and colossal magnetoresistive manganites.In ferroelectric materials,the self-ordering of oxygen vacancies forming linear or planar clusters was proposed to be held responsible for fatigue.and long-term degradation.The formation of oxygen-vacancy clusters in SrTiO3 (STO) was theoretically addressed by first-principle calculation and observed by scanning transition electron microscopy.Until now,however,there has been no direct experimental evidence confirming this clustering process.This is because that oxygen vacancies have already been in the clustered state in the as-prepared crystal.Here we show that uniform distribution of oxygen vacancies at room temperature can be achieved annealing the sample at high temperatures and then quenching to room temperature.The clustering process of oxygen vacancies and related phenomena in the followed heating run can be easily detected by dielectric spectroscopy.This method offers a convenient way to characterize the ordering of oxygen vacancies in the huge family of perovskite materials.