The former is more likely to occur in A-excess samples, while the latter is prevalent in B-excess samples . The solubility of excess Ba 2+ in BaTiO3 is significantly lower than that of excess Ti 4+ , suggesting that more Schottky defects are present in A-site deficient samples. This leads to a larger number of formed oxygen vacancies in the uncompensated BCZT sample which act as mobile charge carriers, increasing the dielectric loss .