Z. G. Yi

Dielectric relaxation studies of Bi-doping effects on the oxygen-ion diffusion in La2−xBixMo2O9 oxide-ion conductors

Two dielectric relaxation peaks associated with oxygen-ion diffusion in the oxide-ion conductors La2−xBixMo2O9 (x=0.05, 0.1, and 0.15) have been studied. It is found that the activation energies of the two peaks increase with increasing Bi-doping concentration, which results from the blocking effects of the lone-pair electrons of Bi3+ ions. From the different effects of Bi doping on the two peaks, the diffusion paths of oxygen ions corresponding to each peak are confirmed. Significantly, it is revealed that Bi doping could enhance the ionic conductivity of La2Mo2O9 at lower temperatures.

Dielectric relaxation studies on the submicron crystalline La2Mo2O9 oxide-ion conductors

Abstract Submicron crystalline La 2 Mo 2 O 9 bulk samples with grain size of about 0.3 μm were successfully synthesized by sol–gel method and sintering process assisted by phase transformation. In the dielectric measurement, two prominent relaxation peaks with almost the same height (P d1 at lower-temperature and P d2 at higher-temperature) are observed in temperature spectrum as well as in frequency spectrum, which are associated with the short-distance diffusion of oxygen vacancies. The activation energies and relaxation times at infinite temperature of these two peaks are deduced as (1.22 eV, 3.3×10 −16 s) and (1.35 eV, 5.9×10 −16 s), respectively. The DC conductivity of the submicron crystalline samples, which is about 0.02 S/cm when extrapolated to 800 °C, is much smaller than that of the macrocrystalline samples. The reciprocal of the peak height for P d1 peak is linearly proportional to temperature, while that for P d2 peak is temperature independent. The reason for the co-appearance and the possible relaxation dynamics of the two peaks are discussed.

Intergrowth Bi2WO6–Bi3TiNbO9 ferroelectrics with high ionic conductivity

This work was supported by the Ministry of Science and Technology of China through 973-Project under Grant No. 2002CB613307.

Lanthanum distribution and dielectric properties of intergrowth Bi5-xLaxTiNbWO15 ferroelectrics

This work was supported by the Ministry of Science and Technology of China through 973-Project under Grant No. 2002CB613307.

Damping mechanism in the novel La2Mo2O9-based oxide-ion conductors

Abstract In this paper, the microscopic diffusion mechanism of oxygen vacancies in the oxygen-ion conductors La 2− x A x Mo 2 O 9 with A=Bi, K and x =0–0.15 are studied by the low frequency internal friction measurements. An internal friction peak associated with the phase transition around 833 K and two relaxation peaks associated with the short-distance diffusion of oxygen vacancies were observed in all samples. With increasing K and Bi doping contents, the activation energies of both relaxation peaks increase; the high-temperature peak decreases in height while the other relaxation peak increases. The phase transition can be completely suppressed by 10% K or 15% Bi doping. It is found that the effect of K-doping is stronger than that of Bi-doping. Combining with the analysis of the crystal structure of La 2 Mo 2 O 9 , the microscopic mechanism of oxygen vacancy diffusion for the two relaxation peaks are suggested.

Ferroelectricity in intergrowth Bi3TiNbO9–Bi4Ti3O12 ceramics

Monophase intergrowth Bi{sub 3}TiNbO{sub 9}-Bi{sub 4}Ti{sub 3}O{sub 12} (BTN-BIT) ceramics were synthesized by solid-state reaction method. In the temperature dependence of dielectric permittivity, two anomalies appeared at 945 and 1114 K, respectively. The ferroelectric hysteresis loop measurement revealed that the 2P{sub r} is 20 {mu}C/cm{sup 2}, nearly as twice as that of the BTN ceramic. The crystal structure analysis indicated that the enhanced octahedral distortion along the a axis is the main contribution to the ferroelectricity of BTN-BIT. The increased 2P{sub r} for the BTN-BIT ceramics is ascribed to its larger P{sub s} than that of the BTN and easier domain switching under electric field than that of the BIT.Monophase intergrowth Bi3TiNbO9–Bi4Ti3O12 (BTN-BIT) ceramics were synthesized by solid-state reaction method. In the temperature dependence of dielectric permittivity, two anomalies appeared at 945 and 1114K, respectively. The ferroelectric hysteresis loop measurement revealed that the 2Pr is 20μC∕cm2, nearly as twice as that of the BTN ceramic. The crystal structure analysis indicated that the enhanced octahedral distortion along the a axis is the main contribution to the ferroelectricity of BTN-BIT. The increased 2Pr for the BTN-BIT ceramics is ascribed to its larger Ps than that of the BTN and easier domain switching under electric field than that of the BIT.

Dielectric and ferroelectric properties of intergrowth Bi7−xLaxTi4NbO21 ceramics

This work was supported by the Ministry of Science and Technology of China through 973-Project No. 2002CB613307, the National Natural Science Foundation of China No. 50572113, and Shanghai Commission of Science and Technology No. 05JC14079.

Dielectric, Impedance, and Electric Modulus Spectroscopies of Mixed-Layer Aurivillius Phase Bi5Ti1.5W1.5O15

Dielectric, impedance, and electric modulus spectroscopies were employed to study the dielectric anomalies in Bi 5 Ti 1.5 W 1.5 O 15 ceramics. It was found that the ferroelectric transition temperature is at 986 K. Besides, two relaxation processes attributed to bulk and grain boundary effects were observed both in the dielectric and impedance spectra. However, only one relaxation process corresponding to the bulk response was observed in the electric modulus spectra. The relaxation parameters were deduced. It was found that the bulk response of the material was of localized relaxation process at low temperatures, and long-range conductivity only emerged at high temperatures. Finally, the relaxation species and dynamics of the bulk response were discussed.

Dielectric relaxation study of Pb1−xLaxMoO4+δ (x = 0–0.3) oxide-ion conductors

DC conductivity and dielectric relaxation measurements are exploited to study the influence of La substitution on the dielectric properties and oxygen-ion transportation in PbMoO4 samples. The DC conductivity of La-doped samples is about 10−3 S cm−1 around 1073 K. A dielectric loss peak with activation energy of 0.6–0.8 eV is observed in the temperature spectrum as well as in the frequency spectrum for all La-doped PbMoO4 samples. With increasing La doping content, this peak becomes higher and shifts to higher temperature or lower frequency, and the activation energy becomes larger. It is suggested that this dielectric loss peak is associated with the short-distance diffusion of oxygen ions (or oxygen vacancies) between the 16f and 8e sites of the scheelite structure type with I41/a symmetry.

Two distinct dielectric relaxation mechanisms in the low-frequency range in Bi5TiNbWO15 ceramics

This work was supported by the Ministry of Science and Technology of China through 973-Project No. 2002CB613307 and the National Natural Science Foundation of China No. 50572113.