Impedance spectroscopy of Bi_3.25La_0.75Ti₃O₁₂ ceramics above and below ferroelectric transition temperatures

다국어 초록 (Multilingual Abstract)

<P>The complex impedance of Bi<SUB>3.25</SUB>La<SUB>0.75</SUB>Ti<SUB>3</SUB>O<SUB>12</SUB> ceramic was measured over a temperature range 50–600 °C at several frequencies. The complex capacitance anomaly of the ferroelectric phase transitions was observed near <I>T</I><SUB>c</SUB> = 395 °C. Remarkable capacitance dispersion of the complex capacitance was found above 250 °C. The complex impedance spectra above 250 °C were fitted by the superposition of two Cole–Cole types of relaxations. The fast component in the higher frequency region may be due to the orientational grain–grain boundary, and the slow component in the lower frequency region is interpreted as the formation and migration of ions at the surface or electrode/crystal interfacial polarization. We found two different conduction mechanisms that have different activation energies: <I>E</I> ∼ 0.33 eV above <I>T</I><SUB>c</SUB> and <I>E</I> ∼ 0.44 eV below <I>T</I><SUB>c</SUB> in the high-frequency regions, and <I>E</I> ∼ 0.32 eV above <I>T</I><SUB>c</SUB> and <I>E</I> ∼ 0.57 eV below <I>T</I><SUB>c</SUB> in the low-frequency regions.</P>