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The ceramic Na0.5Bi0.5Cu3Ti4O12 (sample 1) and 10% mol of Na excessive of Na0.5Bi0.5Cu3Ti4O12 (sample 2) and 10% mol of Bi excessive of Na0.5Bi0.5Cu3Ti4O12 (sample 3) samples were prepared by the standard solid-state reaction technique.The main phase of Na0.5Bi0.5Cu3Ti4O12 is in the three samples.The dielectric properties of samples were investigated as functions of temperature (100 K≤ T ≤ 320 K) and frequency (100 Hz ≤ f ≤ 10 MHz).Our results reveal that either Na or Bi excessive has a great influence on the dielectric properties of Na0.5Bi0.5Cu3Ti4O12.Three thermally activated dielectric relaxations observed with the activation energies of 0.104,0.267,and 0.365 eV for the low-,medium-,and high-temperature dielectric relaxations respectively in sample 1.However,the only one dielectric relaxation appears in sample 2 and sample 3 and the dielectric relaxation activation energy of two samples are nearly the same about 0.090 eV.X-ray photoemission spectroscopy of three samples revealed that the coexistence of Ti3+ and Ti4+ ions is in three samples and mixed oxidation states of Cu (in 1+ and 2+ states) only obtained in sample 1.The dielectric relaxation at low-temperatures of sample 1 is attributed to the carrier hopping process between Ti3+ and Ti4+.