Giant dielectric permittivity observed in pb-based perovskite ferroelectrics

Relaxor ferroelectric-like glassy dielectric dispersion in the triple perovskite Ba3CoSb2O9

In this work, the dielectric response of polycrystalline Ba3CoSb2O9 was studied as a function of temperature (30 to 900 °C) and frequency (10 Hz to 10 MHz). The triple perovskite Ba3CoSb2O9 was successfully synthesized and characterized for structural and dielectric properties. The Rietveld analysis of the X-ray diffractogram confirms the formation of a hexagonal phase with P63/mmc symmetry. This centrosymmetric 3(BaCo1/3Sb2/3O3) perovskite shows structural similarity to a prototypical non-centrosymmetric relaxor ferroelectric, PbMg1/3Nb2/3O3. The dielectric constant, ε', follows a non-Debye Cole-Cole relation and exhibits anomalous responses such as: (a) a thermally activated colossal dielectric constant (>105) and (b) a highly dispersive peak maximum (523-853 K). The real part of ac conductivity, σ', also shows a change of approximately 6 orders in magnitude (10-8 to 10-2 S m-1). Validation of Jonscher's law and impedance (Nyquist plot) and modulus (M'') analyses indicate that hopping polarization is the predominant thermally activated mechanism. Moreover, the large value of ε' and its dispersion were found to be highly correlated with the underlying crystal structure and were attributed to the local ionic site ordering. The study suggests that the anomalous dielectric dispersion must have an intrinsic origin.

Transport and Dielectric Properties of Mechanosynthesized La2/3Cu3Ti4O12 Ceramics

La2/3Cu3Ti4O12 (LCTO) powder has been synthesized by the mechanochemical milling technique. The pelletized powder was conventionally sintered for 10 h at a temperature range of 975–1025 °C, which is a lower temperature process compared to the standard solid-state reaction. X-ray diffraction analysis revealed a cubic phase for the current LCTO ceramics. The grain size of the sintered ceramics was found to increase from 1.5 ± 0.5 to 2.3 ± 0.5 μm with an increase in sintering temperature from 975 to 1025 °C. The impedance results show that the grain conductivity is more than three orders of magnitude larger than the grain boundary conductivity for LCTO ceramics. All the samples showed a giant dielectric constant (1.7 × 103–3.4 × 103) and dielectric loss (0.09–0.17) at 300 K and 10 kHz. The giant dielectric constant of the current samples was attributed to the effect of internal barrier layer capacitances due to their electrically inhomogeneous structure.

Structural Distortion and Dielectric Permittivities of KCoO2-Type Layered Nitrides Ca1-xSrxTiN2

Among the KCoO₂-type phases, the orthorhombic layered nitride CaTiN₂ is a newly reported high dielectric permittivity material (ε_r ∼ 1300-2500 within 10⁴-10⁶ Hz from 80 to 450 K) while the tetragonal SrTiN₂ is reported to display an unintentional metallic conduction property. In this work, a Ca_1-xSr_xTiN₂ solid solution was synthesized, in which the insulating SrTiN₂ end member and some Sr-doped CaTiN₂ samples were successfully obtained, and therefore, the dielectric properties of the Ca_1-xSr_xTiN₂ solid solution were investigated. The Sr substitution for Ca drove an orthorhombic-to-tetragonal phase transformation in Ca_1-xSr_xTiN₂, which reduced the dielectric permittivity significantly. The tetragonal SrTiN₂ displays a much lower dielectric permittivity (ε_r ∼ 20-70 in 10⁵-10⁶ Hz and 10-300 K) than that of CaTiN₂. The comparison on the dielectric permittivities and structures of CaTiN₂ and SrTiN₂ indicates that the structural distortion arising from the splitting of N planes between Ti layers within the TiN₂ pyramidal layers could be a plausible structural origin of the high bulk dielectric permittivity of CaTiN₂.

Investigation of Dielectric Properties, Electric Modulus and Conductivity of the Au/Zn-Doped PVA/n-4H-SiC (MPS) Structure Using Impedance Spectroscopy Method

The 50 nm thickness Zn-doped polyvinyl alcohol (PVA) was deposited on n-4H-SiC semiconductor as interlayer by electro-spinning method and so Au/Zn-doped PVA/n-4H-SiC metal-polymer-semiconductor (MPS) structure were fabricated. The real and imaginary parts of the complex dielectric constant (ε′, ε′′), loss-tangent (tan δ), the real and imaginary parts of the complex electric modulus (M′, M′′) and ac electrical conductivity (σ ac ) behavior of this structure were examined using impedance spectroscopy method in a wide range of frequency (1 kHz–400 kHz) and voltage (−1 V)–(+6 V) at room temperature. The values of ε′, ε′′, tan δ, M′, M′′ and σ ac are determined sensitive to the frequency and voltage in depletion and accumulation regions. The values of ε′ and ε′′ decrease with increasing frequency while the values of M′ and σ ac increase. The peak behavior in the tan δ and M′′ vs. frequency curves was attributed to the dielectric relaxation processes and surface states (Nss ). The plots of ln (σ ac ) vs. ln (f) at enough high forward bias voltage (+6 V) have three linear regions with different slopes which correspond to low, intermediate and high frequencies, respectively. The dc conductivity is effective at low frequencies whereas the ac conductivity effective at high frequencies. According to experimental results, the surface/dipole polarizations can occur more easily occur at low frequencies and the majority of Nss between Zn-doped PVA and n-4H-SiC contributes to the deviation of dielectric behavior of this structure.

Comparison of Electrophysical Properties of PZT-Type Ceramics Obtained by Conventional and Mechanochemical Methods

In the paper, the multicomponent PZT-type ceramics with Pb(Zr_0.49Ti_0.51)_0.94Mn_0.015Sb_0.01W_0.015Ni_0.03O₃ composition have been obtained by conventional and mechanochemical methods. With conventional ceramic technology, PZT-type ceramics have been synthesized by the method of calcination powder (850 °C/4 h). Instead of this step, the mechanochemical synthesis process for different milling periods (15 h, 25 h, 50 h, 75 h) has been applied for a second batch of samples. To obtain the dense PZT-type ceramic samples, powders have been sintered by free sintering method at conditions of 1150 °C/2 h. Studies have shown that the perovskite structure of the PZT-type material is formed during mechanochemical activation of powders during the technological process at low temperature. The application of the mechanochemical synthesis to obtain the PZT-type materials also allows shortening of the technological process, and the useful electrophysical properties of ceramic samples are not reduced at the same time. The presented results have confirmed that the investigated materials can be used in microelectronic applications, especially as elements of actuators and piezoelectric transducers.

Reduced dielectric loss in new colossal permittivity (Pr, Nb)TiO2 ceramics by suppressing adverse effects of secondary phases

Here, we develop new colossal permittivity (CP) (Pr0.5Nb0.5)xTi1-xO2 ceramics by controlling the secondary phases, and then both colossal permittivity (εr = 6-8 × 104, 1 kHz) and low dielectric loss (tan δ = 3.7-7.5%, 1 kHz) can be realized in a composition range (x = 0.5-2.5%). The ceramics with x = 1% possess a high dielectric constant (εr = 74 533), and importantly a low dielectric loss (tan δ = 3.7%) can be found, which is lower than most of the typical CP materials and chemically modified TiO2 ceramics. In addition, the εr changing rates of 143 per degree Celsius and 35 per kiloHertz indicate an excellent temperature and frequency stability of the dielectric behaviors. XRD, FE-SEM and element mapping are conducted to probe the secondary phases, and element line scanning is used to explore the elemental composition of the secondary phases. The test results indicate that optimized dopants can enhance the dielectric properties, while secondary phases induced by x > 5% dopants can cause adverse effects on the dielectric properties. XPS results further demonstrate that the defect-dipole theory may be suitable to explain the significant improvement of dielectric properties. We believe that (Pr, Nb)TiO2 ceramics are one of the most competitive candidates in the field of electronic and energy-storage devices.

Effects of Secondary Phases on the High-Performance Colossal Permittivity in Titanium Dioxide Ceramics

The intensive demands of microelectronics and energy-storage applications are driving the increasing investigations on the colossal permittivity (CP) materials. In this study, we designed a new system of Dy and Nb co-doped TiO₂ ceramics [(Dy_0.5Nb_0.5)_xTi_1-xO₂] with the formation of secondary phases, and then the enhancement of overall dielectric properties (ε_r ∼ 5.0-6.5 × 10⁴ and tan δ < 8%) was realized in the broad composition range of 0.5 ≤ x ≤ 5%. More importantly, effects of secondary phases on microstructure, dielectric properties, and stability were explored from the views of defect-dipoles and internal barrier layer capacitance (IBLC) effect. According to the defect-dipoles theory, the CP should mainly originate from Nb⁵⁺, and the Dy³⁺ largely contributes to the decreased dielectric loss. Both CP and low dielectric loss were obtained for co-doping with Dy³⁺ and Nb⁵⁺. Besides, the Dy enrichment induced the formation of secondary phases, which were regarded as the low loss unit dispersed into the ceramic matrix, and largely facilitate the decreased dielectric loss. In particular, the analysis of temperature-dependent complex impedance spectra indicated that a stronger IBLC effect caused by the increased grain boundary resistance can also contribute to the optimized CP and low dielectric loss under appropriate contents of secondary phases.

Colossal dielectric permittivity in Co-doped ZnO ceramics prepared by a pressure-less sintering method

Dielectric properties and impedance spectroscopic studies of single phase Zn_1−xCo_xO (0 ≤ x ≤ 0.05) ceramics, synthesized by a pressure-less solid state reaction method, have been carried out to investigate the origin of colossal dielectric permittivity (CP), ε′ ∼ 10⁵, in a wide frequency (2 × 10¹–2 × 10⁶ Hz) range.

Frequency and temperature-dependence of dielectric permittivity and electric modulus studies of the solid solution Ca0.85Er0.1Ti1−xCo4x/3O3 (0 ≤ x ≤ 0.1)

The dielectric properties of Ca_0.85Er_0.1Ti_1−xCo_4x/3O₃ (CETCo_x) (x = 0.00, 0.05 and 0.10), prepared by a sol–gel method, were systematically characterized. The temperature and frequency dependence of the dielectric properties showed a major effect of the grain and grain boundary. The dielectric constant and dielectric loss of CETCo_x decreased sharply with increasing frequency. This is referred to as the Maxwell–Wagner type of polarization in accordance with Koop's theory. As a function of temperature, the dielectric loss and the real part of permittivity decreased with increasing frequency as well as Co rate. Indeed, a classical ferroelectric behavior was observed for x = 0.00. The non-ferroelectric state of the grain boundary and its correlation with structure, however, proved the existence of a relaxor behavior for x = 0.05 and 0.10. The complex electric modulus analysis M*(ω) confirmed that the relaxation process is thermally activated. The normalized imaginary part of the modulus indicated that the relaxation process is dominated by the short range movement of charge carriers.

Frequency dependence of real (ε′) part of permittivity of CETCo_x for x = 0.00, 0.05 and 0.10 for T = 600 K.

Experimental and theoretical investigation of the high dielectric permittivity of tantalum doped titania

High dielectric permittivity is observed due to conducting grains and insulating grain boundaries.

Colossal permittivity and impedance analysis of niobium and aluminum co-doped TiO2 ceramics

Niobium and aluminum co-doped TiO₂ ceramics, i.e., (Nb_0.5Al_0.5)_xTi_1−xO₂ (x = 0, 0.01, 0.05, 0.1, 0.15, abbreviated as NAT100x) were synthesized via a solid-state reaction route.

Enhancement of dielectric constant in a niobium doped titania system: an experimental and theoretical study

A very high dielectric constant of Nb doped titania is observed due to both the interfacial effect and formation of complex defect dipoles.

Quasi-intrinsic colossal permittivity in Nb and In co-doped rutile TiO2 nanoceramics synthesized through a oxalate chemical-solution route combined with spark plasma sintering

Nb and In co-doped rutile TiO2 nanoceramics (n-NITO) were successfully synthesized through a chemical-solution route combined with a low temperature spark plasma sintering (SPS) technique. The particle morphology and the microstructure of n-NITO compounds were nanometric in size. Various techniques such as X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), thermogravimetric (TG)/differential thermal analysis (DTA), Fourier transform infrared (FTIR), and Raman spectroscopy were used for the structural and compositional characterization of the synthesized compound. The results indicated that the as-synthesized n-NITO oxalate as well as sintered ceramic have a co-doped single phase of titanyl oxalate and rutile TiO2, respectively. Broadband impedance spectroscopy revealed that novel colossal permittivity (CP) was achieved in n-NITO ceramics exhibiting excellent temperature-frequency stable CP (up to 10(4)) as well as low dielectric loss (∼5%). Most importantly, detailed impedance data analyses of n-NITO compared to microcrystalline NITO (μ-NITO) demonstrated that the origin of CP in NITO bulk nanoceramics might be related with the pinned electrons in defect clusters and not to extrinsic interfacial effects.

Polymer Composite and Nanocomposite Dielectric Materials for Pulse Power Energy Storage

This review summarizes the current state of polymer composites used as dielectric materials for energy storage. The particular focus is on materials: polymers serving as the matrix, inorganic fillers used to increase the effective dielectric constant, and various recent investigations of functionalization of metal oxide fillers to improve compatibility with polymers. We review the recent literature focused on the dielectric characterization of composites, specifically the measurement of dielectric permittivity and breakdown field strength. Special attention is given to the analysis of the energy density of polymer composite materials and how the functionalization of the inorganic filler affects the energy density of polymer composite dielectric materials.

Relationship between local structure and relaxor behavior in perovskite oxides

Despite intensive investigations over the past five decades, the microscopic origins of the fascinating dielectric properties of ABO3 relaxor ferroelectrics are currently poorly understood. Here, we show that the frequency dispersion that is the hallmark of relaxor behavior is quantitatively related to the crystal chemical characteristics of the solid solution. Density functional theory is used in conjunction with experimental determination of cation arrangement to identify the 0 K structural motifs. These are then used to parametrize a simple phenomenological Landau theory that predicts the universal dependence of frequency dispersion on the solid solution cation arrangement and off-center cation displacements.

Giant dielectric permittivity observed in Li and Ti doped NiO

A giant low-frequency dielectric constant ( epsilon 0 approximately 10(5)) near room temperature was observed in Li,Ti co-doped NiO ceramics. Unlike currently best-known high epsilon 0 ferroelectric-related materials, the doped oxide is a nonperovskite, lead-free, and nonferroelectric material. It is suggested that the giant dielectric constant response of the doped NiO could be enhanced by a grain boundary-layer mechanism as found in boundary-layer capacitors. In addition, there is about a one-hundred-fold drop in the dielectric constant at low temperature. This anomaly is attributed to a thermally excited relaxation process rather than a thermally driven phase transition, as for that yielding ferroelectrics.

Optical response of high-dielectric-constant perovskite-related oxide

Optical conductivity measurements on the perovskite-related oxide CaCu3Ti4O12 provide a hint of the physics underlying the observed giant dielectric effect in this material. A low-frequency vibration displays anomalous behavior, implying that there is a redistribution of charge within the unit cell at low temperature. At infrared frequencies (terahertz), the value for the dielectric constant is approximately 80 at room temperature, which is far smaller than the value of approximately 10(5) obtained at lower radio frequencies (kilohertz). This discrepancy implies the presence of a strong absorption at very low frequencies due to dipole relaxation. At room temperature, the characteristic relaxation times are fast (less than or approximately 500 nanoseconds) but increase dramatically at low temperature, suggesting that the large change in dielectric constant may be due to a relaxor-like dynamical slowing down of dipolar fluctuations in nanosize domains.