Debye-type Polarization Research Articles

Electrical Conductivity and Dielectric Constant of Novel Proton Conductor Ba2(Zn, M)2O6-δ (M = W, Nb) Having Oxygen Deficient Perovskite Structure

Ba2(Zn1-xMx)2O6-δ (M = W, Nb) systems, where the oxygen vacancy concentration can be controlled by the Zn/M ratio, were found to have cubic double-perovskite-type structure for M = W and cubic perovskite-type structure for M=Nb. As it was found by thermogravimetry that the Ba2(Zn1-xMx)2O6-δ samples can uptake the large amount of H2O, we expected that the adsorption of H2O may contribute to a generation of proton conduction. Then, the electrical conductivity was measured in dry and humid Ar atmospheres by the two-probe method. The electrical conductivity remarkably increased in the humid atmosphere, suggesting occurrence of the proton conduction. The numerical calculation of frequency dependences of dielectric constant (ɛr’) were successfully explained by the superposition of Debye-type polarizations and electrolyte-electrode interfacial.

Dielectric Properties and Oxide-Ion Conduction for Y2O3 Stabilized ZrO2 and Bi2O3

The oxide-ion conduction and dielectric properties of 8 mol % Y2O3 stabilized ZrO2 (8YSZ) and 25 mol % Y2O3 stabilized Bi2O3 (25YSB) which are oxide ion conductors having a fluorite type structure were investigated. The numerical analyses for the frequency dependences of dielectric constants (εr') and dielectric loss factors (εr'') revealed that the dielectric properties were explained by Debye-type polarization due to dopant–vacancy associates and/or polarization due to charging or loss current. No Debye-type polarization was observed in 25YSB because of no effective charge at the Y3+-doped Bi3+ site. On the other hand, three Debye-type dipoles observed in 8YSZ were assigned to the polarization of oxide-ion conduction, and two kinds of associates, [YZr'–Vo••]• and [YZr'–Vo••–YZr']×, due to the interaction between doped cation (YZr') and oxygen vacancy (Vo••). The frequency dependence of dielectric loss tangent (tan δ) in 25YSB was ascribed to the interface loss due to the charged current, while that of tan δ in 8YSZ was ascribed to the Debye-type dipoles in addition to the interface loss.

Oxide-ion conduction and dielectric relaxations for fluorite type structure

The oxide-ion conduction and dielectric properties of 10 mol% CaO stabilized ZrO2 (10CSZ) and 25 mol% Y2O3 stabilized Bi2O3 (25YSB) which are oxide ion conductors having a fluorite-type structure were investigated. The numerical analyses for the frequency dependences of dielectric constants (ϵr′) and dielectric loss factors (ϵr′′) revealed that the dielectric properties were explained by Debye-type polarization due to dopant-vacancy associates and/or electrolyte-electrode interfacial polarization due to charging or loss current. No Debye-type polarization was observed in 25YSB because of no effective charge at the Y3+-doped Bi3+ site. On the other hand, two Debye-type dipoles observed in 10CSZ were assigned to two kinds of associates, [CaZr′′-Vo··]·, which was due to dopant-vacancy associates with two different distances between (CaZr′′) and (Vo··). The frequency dependence of dielectric loss tangent (tanδ) in 25YSB was ascribed to the interface loss due to the charged current, while that of tanδ in 8YSZ was ascribed to the Debye-type dipoles in addition to the interface loss.

Oxide-ion conduction and dielectric relaxation in the fluorite-type Zr0.8Ln0.2O1.9 (Ln = Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb, Lu) system

The electrical conductivity and dielectric properties of the Zr0.8Ln0.2O1.9 (Ln = Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb, Lu) system which have a cubic fluorite-type structure were investigated in order to clarify a dynamic property of oxygen vacancy in oxide-ion conductors. The frequency dependences of dielectric constants (ϵr′) were successfully explained by the superposition of Debye-type polarizations and electrolyte-electrode interfacial polarizations. The ac conductivity (σac) agreed with the calculated values using the dielectric parameters. It was found that the compositional dependence of dielectric properties was similar to that of σac.

Debye process and dielectric state of an alcohol in a nonpolar solvent

To investigate the origin of the first order molecular kinetics of the most prominent, Debye-type polarization, a detailed dielectric relaxation study of 66.5, 40, and 20 mole% solutions of 5-methyl-2-hexanol in 2-methylpentane (2:1, 0.67:1, and 0.25:1 molar ratios) was performed. The Debye-type polarization remains prominent in the solutions, despite the extensive loss of intermolecular hydrogen bonds. At high temperatures, its contribution to permittivity extrapolates close to the statistically scaled values for the 2:1 solution. For others, the measured values of its contribution crossover the scaled values in a temperature plane. The faster relaxation process of about 4% magnitude has an asymmetric distribution of times in the solutions and, relative to those of the pure alcohol, their values decrease on heating more at high temperatures and less at low. This is attributed to an increase in the alcohol cluster size by consumption of monomers as well as the growth of smaller clusters as the solution is cooled. It is argued that structural fluctuation in solutions, as in the pure alcohol, is determined by the rates of both the Debye-type and the faster polarizations in the ultraviscous state.

Relationship between Dielectric Properties and Oxygen Defect Structure of Nondoped CeO2

The dielectric properties of CeO2, which was annealed at 1273 K in O2, air, and Ar atmospheres for the as-sintered specimens, were investigated in the temperature range from 673 to 1073 K. The frequency dependences of dielectric constant (εr') and dielectric loss factor (εr'') were successfully explained by Debye-type polarization model. The observed values of dielectric loss tangent (tan δ) and ac electrical conductivity (σac) agreed with the values calculated using the dielectric parameters estimated from the analyses of εr' and εr''. It was found that the dielectric parameters such as Debye-type polarization (εro1), relaxation frequency (ωo1), and ac conductivity (σac) increased with increasing oxygen vacancy concentration, which depends on the oxygen partial pressure in the annealing atmospheres.

Relationship between Oxide-Ion Conduction and Dielectric Properties of Gd2Zr2O7 Having a Fluorite-Type Structure

The relationship between electrical conduction and dielectric properties was investigated for the oxide-ion conductor Gd2Zr2O7 having a fluorite-type structure. Computer simulation clarified that the anomalously large dielectric constant (εr') was successfully explained by the superposition of the Debye-type polarization and the electrolyte–electrode interfacial polarization. Two Debye-type relaxations were observed at 673 K and above. The lower-frequency relaxation was ascribed to the dopant–vacancy associate, (GdCe'–VO••–GdCe'), and the higher one to the long range migration of oxide ions on the basis of the discussions of both the activation energies and the relaxation frequencies. The frequency dependences of both the ac conductivity (σac) and the loss tangent (tan δ) were also successfully explained using the dielectric parameters of the Debye-type dopant–vacancy associates.

Relationship between oxide-ion conductivity and dielectric relaxation in the Ln 2Zr 2O 7 system having pyrochore-type compositions (Ln=Yb, Y, Gd, Eu, Sm, Nd, La)

Ln 2Zr 2O 7 (Ln=Yb, Y, Gd, Eu, Sm, Nd, La) system changed from fluorite (F)-type to pyrochlore (P)-type phases when the ionic radius ratios, r(Ln 3+)/ r(Zr 4+), were larger than 1.26. The oxide-ion conductivity showed sharp maximum at the vicinity of the phase boundary between the F- and P-type phases. The frequency dependence of dielectric constant ( ε r ′ ) and dielectric loss factor ( ε r ″ ) were successfully explained by the superimposition of Debye-type polarization due to dopant-vacancy associate and electrode–electrolyte interfacial polarization by the numerical calculation. The peak of dielectric loss tangent (tan δ) was ascribed to the dopant-vacancy associate. The ε r (0) and dielectric constant of the associate ( ε r 0) showed also the maximum values at the vicinity of the phase boundary between the F- and P-type phases.

Dielectric properties of proton conductor BaCe0.9Y0.1O3-.DELTA.

Frequency dependences of the dielectric constant (er′) were investigated for the perovskite-type oxide BaCe0.9Y0.1O3-δ, which is a typical proton conductor. Numerical calculation of the frequency dependence of er′ clarified that the large er′ originated from the superimposition of both electrolyte-electrode interfacial and Debye-type polarizations. The Debye-type polarizations which originated from the dopant-vacancy associates, (YCe′-VO••)• were depressed under wet Ar atmosphere. Therefore, it can be speculated that the proton may occur according to the following equilibrium equation: H2O+VO••⇔2H•+OO×.

Proton conductivity of perovskite types oxide BaCe<sub>1-x</sub>Y<sub>x</sub>O<sub>3-δ</sub>

Frequency dependences of dielectric constant (epsilon r'), electrical conductivity and weight change were investigated for the perovskite-type oxide system BaCe1-xYxO3-delta (x=0.05~0.l5), which is a typical proton conductor. The sample with x=0.15 showed the maximum values in both proton conductivity and water content. Numerical calculation of frequency dependence of epsilon r' clarified that the large epsilon r' originates from the superimposition of both electrolyte-electrode interfacial and Debye-type polarizations. The Debye-type polarizations which are ascribed to the dopant-vacancy associates, (Yce' -Vo..) ·are depressed under wet Ar atmosphere. The decrease in the dipole showed the maximum at x=0.15. Therefore, it can be speculated that the proton may occur according to the following equilibrium equation, H2O + Vo.. ·= 2H. ·+ Oox.

Dielectric Relaxations in the Ce1-xYbxO2-δ System

The dielectric properties of Yb-doped CeO2 (Ce1-xYbxO2-δ) which is an oxide-ion conductor were investigated. Numerical analysis of the frequency dependences of dielectric constants (ε') and dielectric loss factors (ε'') revealed that the dielectric characteristics can be successfully explained by the superimposition of both Debye-type polarization due to dopant-vacancy associates and electrolyte–electrode interfacial polarization. The temperature response of the dielectric properties was less active than that of the Sm- or Nd-doped CeO2 systems, which have higher oxide-ion conductivity than the present system. Three types of Debye-type polarizations were observed. The first polarization at the highest-frequency region was ascribed to a long-range migration of oxygen vacancies. The second and third polarizations at the lower-frequency region were ascribed to the dopant-vacancy associates. The observed values of σac and tan δ were also successfully explained using the dielectric parameters that were obtained from the numerical analysis of dielectric constant.

Electrode Effects for Dielectric Properties of 8 mol% Y2O3 Stabilized ZrO2

The frequency dependences of dielectric constant (er′) for 8 mol% Y2O3 stabilized ZrO2 (8YSZ) with two kinds of electrodes, Pt and La0.6Ca0.4MnO3 (LCM), were successfully explained by the superposition of both electrolyte-electrode interfacial polarizations and Debye-type polarizations due to dopant-vacancy associates. The different behaviors in the frequency dependence of er′ for 8YSZ having the different electrodes were ascribed to the dopant-vacancy associates, (YZr′–VO••) and (YZr′–VO••–YZr′), which were very large for 8YSZ with Pt electrode, but almost disappeared for 8YSZ with LCM electrode. The frequency dependences of the ac conductivity (σac) were also explained by the relaxation phenomena of the dopant-vacancy associates, suggesting that the dispersion of σac can not be ascribed to grain boundary effect of electrolyte.

Dielectric relaxations in the Ce 1− xNd xO 2− δ system

Dielectric relaxations were investigated for the solid solution system Ce 1− x Nd x O 2− δ (0.0 ≦ x ≦ 0.5) having a fluorite-type structure, which is a typical oxide-ion conductor. The dielectric constants showed anomalously large values at low frequencies and high temperatures. Numerical analysis of frequency dependence of dielectric constant ( ε r′) clarified that the anomalously large ε r′ originated from the superimposition of both Debye-type polarization and interfacial polarization between electrolyte and electrode. Two kinds of Debye-type relaxations observed were ascribed to defect associates, (Nd Ce′ − V O¨) · and (Nd Ce′ − V O¨ − Nd Ce′) x . The Debye-type polarizations were also confirmed by analyzing the dielectric loss factor ( ε r″). When the oxide-ion conductivity decreased in the heavy Nd-doped samples, both the Debye-type and the interfacial polarizations also decreased, suggesting that ordering of oxygen vacancy suppressed the electric field response of Debye-type polarization, resulting in the decrease of oxide-ion conductivity.

Relationship between oxide-ion conductivity and dielectric relaxation in Sm-doped CeO 2

The relationship between electrical conduction and dielectric relaxation was investigated for 20 at.% Sm doped CeO 2 (Ce 0.8Sm 0.2O 2− δ ), which is a typical oxide-ion conductor. Numerical calculation clarified that the anomalously large dielectric constant ( ε r′) originated from the superimposition of both Debye-type polarization and interfacial polarization between electrolyte and electrode. Two kinds of the Debye-type relaxation appeared at and above 673 K, which were assigned to defect associates, (Sm Ce′–V O ) and (Sm Ce′–V O –Sm Ce′) x . The Debye-type polarization was also confirmed by analyzing the dielectric loss factor ( ε rʺ). Ac conductivity ( σ ac) in high temperature and high frequency regions agreed with dc conductivity ( σ dc), while the dispersion of σ ac was ascribed to the Debye-type polarizations.

Dielectric Relaxations in the Ce1-xSmxO2-.DELTA. System

Dielectric relaxations were investigated for the solid-solution system Ce1-xSmxO2-δ(0.0≦x≦0.5), which is a typical oxide-ion conductor. The dielectric constants showed anomalously large values at low frequencies and high temperatures. Computer simulation clarified that the anomalously large dielectric constant (er′) originated from the superimposition of both Debye-type polarization and interfacial polarization between electrolyte and electrode. Two kinds of Debye-type relaxation observed were ascribed to defect associates, (SmCe′-VO••)• and (SmCe′-VO••-SmCe′)×. The Debye-type polarization was also confirmed by analyzing the dielectric loss factor (er″). When the oxide-ion conductivity decreased in the heavy Sm-doped samples, the Debye-type polarization also disappeared, suggesting that ordering of oxygen vacancy suppressed the electric field response of Debye-type polarization.

Dielectric Relaxations of Y-Doped ZrO2 Single Crystal

Frequency dependences of dielectric constant (e r ') for 9 mol% Y 2 O 3 doped ZrO 2 (YSZ) single crystal which is a typical oxide-ion conductor was successfully explained by the superimposition of both electrolyte-electrode interfacial and Debye-type polarizations. Three kinds of Debye-type polarizations were observed at fairly high temperatures. The two polarizations were ascribed to defect associates, (Yz r '-Vo)°, which were observed in the tan spectra. The third polarization in the high frequency region was ascribed to a long range migration of oxygen vacancy, which was observed in the M spectra. The σ ac dispersion was also explained by the Debye-type polarizations.

Dielectric Relaxations in the Ca-Doped CeO<sub>2</sub> System

Dielectric relaxations were investigated for 10 mol% Ca-doped CeO 2 (Ce 0.9 Ca 0.1 O 2-5 ) having a cubic fluorite-type structure, which is a typical oxide-ion conductor. The dielectric constants (e r ) showed anomalously large values at low frequencies and high temperatures. Numerical analysis of the frequency dependence of e r clarified that the large e r , originated from superimposition of both the electrolyte-electrode interfacial and Debye-type polarizations. The ac conduction dispersion was also successfully explained by the interfacial and Debye-type polarizations. Two kinds of Debye-type relaxations observed were ascribed to defect associates, (Ca ce -Vo) which have different distances between the dopant and the oxygen vacancy.

Relationship between Oxide-Ion Conductivity and Dielectric Relaxation in 20 atom% Nd-Doped CeO2

The relationship between electrical conductivity and dielectric relaxation was investigated for 20 atom % Nd doped CeO2 (Ce0.8Nd0.2O2−δ), which is a typical oxide-ion conductor. Computer simulation clarified that the anomaly large dielectric constant (εr′) originated from the superimposition of both Debye-type polarization and interfacial polarization between electrolyte and electrode. Two kinds of the Debye-type relaxation appeared equal and above 773 K, which were ascribed to defect associates, (NdCe′-VO••)• and (NdCe′-VO••-NdCe′)×. The frequency dependence of ac conductivity (σac) was successfully explained by analyzing the dielectric loss factor (εr″). The σac values in high temperature and high frequency regions agreed with dc conductivity (σdc). The activation energy for σdc agreed with that for high frequency Debye-type polarization.

Relationship between Oxide-Ion Conductivity and Dielectric Constant in Ce0.9Sm0.1O2-.DELTA.

The relationship between electrical conductivity and dielectric constant was investigated for 10 atom%Sm doped CeO 2 (Ce 0.9 Sm 0.1 Ο 2-δ ), which is a typical oxide-ion conductor. Computer simulation clarified that anomalously large dielectric constant originated from the superimposition of both Debye-type dipole and interfacial polarization between electrolyte and electrode. The interfacial polarization was proportional to the inverse of the frequency, suggesting the accumulation of oxide ions at the interfacial sites with high-energy barriers due to the oxide-ion conduction. Ac conductivity (σ ac ) at high temperatures and high frequencies agreed with the σ dc value, but lowered in such a frequency region that the Debye-type polarization appeared. The activation energy for σ dc agreed with those for Debye-type polarization and interfacial polarization, suggesting that these thermal exciting processes originate from oxide-ion diffusion.

Dynamical Aspects of Retention and its Relation to Fatigue in Ferroelectric Thin Films

Short-time retention loss behaviors were investigated for fatigued Pt/PbZr0.4Ti0.6O3/Pt capacitors. In the short-time regime of t<1 s, fatigued capacitors showed a significant loss in retained polarization. The short-time retention loss behavior was well described by a power-law function and the retention characteristic got worse as the fatigue stress increased. The retention loss was analyzed in a viewpoint of polarization dynamics, superpositions of Debye-type polarization relaxations. Distribution of the relaxation time was affected by the degree of fatigue stress and write/read pulse-field strength. The results were explained in terms of the depolarization field.