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Mn(4+)-rich perovskite manganites (nominal composition: Pr(0.1)Ca(0.9)MnO(3)) were synthesized by using a citric acid method and sintered at different temperatures (800, 900, 1000, and 1300 degrees C) to adjust the concentration of charge carrier. All the samples are found to be in the cluster glass state at low temperature, as indicated by dc and ac magnetization. With the increase of sintering temperature, the ferromagnetic component in samples increases at first, and attains a maximum at 1000 degrees C, then decreases again at 1300 degrees C, which could be well interpreted by the change of charge carrier concentration induced by nonstoichiometry, consistent with the trend on the phase diagram. However, nonstoichiometry breaks long-range Mn-O-Mn interaction, resulting in the variance from the phase diagram. (C) 2008 Published by Elsevier B.V.