Dielectric Relaxation and Magnetic Structure of A-Site-Ordered Perovskite Oxide Semiconductor CaCu3Fe2Ta2O12.

A new perovskite oxide semiconductor, CaCu3Fe2Ta2O12, was synthesized through a high-pressure and high-temperature approach. The compound possesses an Im3̅ space group, where it crystallizes to an A-site-ordered but B-site partial ordered quadruple perovskite structure. Spin ordering occurs around 150 K owing to the antiferromagnetic coupling between Fe3+ spins and ferromagnetic coupling between Cu2+ spins. The room-temperature dielectric permittivity of CaCu3Fe2Ta2O12 was measured to be approximately 2500 at 1 kHz. More importantly, isothermal frequency-dielectric spectroscopy demonstrates the existence of two dielectric relaxations. Debye-like relaxation is attributed to charge carriers trapped among the oxygen vacancies at low temperatures and Maxwell-Wagner polarization relaxation at high temperatures. CaCu3Fe2Ta2O12 is a new magnetic semiconductor, where A-site ordering is intercorrelated with second-order Jahn-Teller distortion. These findings offer opportunities to design novel perovskite oxides with attractive magnetic and dielectric properties.