Effect of La doping on the suppression of insulation resistance degradation in multi-layer ceramic capacitors (MLCCs) was investigated. The insulation resistance of La-doped (Ba, Sr)(Ti, Zr)O3 (La-doped BSTZ) MLCCs increased during the early phase of the highly accelerated life test (HALT). The insulation resistance of La-doped BSTZ-MLCCs immediately before breakdown was still higher than that at the early phase. This behavior during the early phase of HALT was eminent for La doping. However, the activation energy of the La-doped BSTZ-MLCCs was the same as those of other rare earth element-doped BaTiO3 MLCCs, suggesting that La-doped BSTZ-MLCCs were also degraded by the migration of oxygen vacancies. Thermally stimulated depolarization current analysis revealed that La-doped BSTZ-MLCCs exhibited trapping of the oxygen vacancies around the grain boundary, which suggested that trapping led to suppression of migration of the oxygen vacancies, and decreased polarization current. This trapping resulted in an increased insulation resistance.
BaTiO 3 (Bi 1/2 Na 1/2 )TiO 3 (abbreviated as BTBNT) solid solution semiconducting ceramics, as a candidate for a lead-free PTC (Positive Temperature Coefficient of resistivity) thermistor usable over 130°C, were synthesized by adding CaO into the calcined powder. The CaO added BTBNT ceramics showed semiconducting behavior with the resistivity at room temperature µ RT = 10 3 ³ cm and a resistivity change near Curie temperature. Chemical composition analysis suggested that Ca 2+ acted as a donor by substituting for Na + in the BTBNT ceramics.
BaTiO3–(Bi1/2Na1/2)TiO3(abbreviated as BT-BNT) solid solution ceramics, as a lead-free PTC (Positive Temperature Coefficient of resistivity) thermistor material usable over 130°C, were synthesized in air atmosphere. By conventional processes, La-doping was not effective in giving semiconducting property to the BT-BNT ceramics because of volatilization of sodium and bismuth during sintering. By preventing the volatilization by lowering the sintering temperature using very fine TiO2powder and by adding calcium oxide to calcined BT-BNT powders, we obtained BT-BNT semiconducting ceramics which shows a resistivity change near Curie temperature.
BaTiO3–(Bi1/2K1/2)TiO3 (abbreviated as BT-BKT) solid solution ceramics, as a lead-free PTC (positive temperature coefficient of resistivity) thermistor material usable over 130°C, has been synthesized by sintering in N2 atmosphere and after annealing in air over 1200°C. In the BT-BKT ceramics with PTC property, the impedance/modulus spectroscopic plots have revealed that a third resistance-capacitance (RC) response besides grains and grain boundaries. Using the remote electron beam induced current (REBIC) configuration, imaging has revealed EBIC contrast consistent with the presence of negatively charged electrostatic grain boundary barriers in the BT-BKT semiconducting ceramics.
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