Colossal Dielectric Permittivity Research Articles

Compositional modulation and annealing treatment in BaTiO3 to simultaneously achieve colossal permittivity, low dielectric loss, and high thermal stability

Holmium doped BaTiO3 ceramics were prepared by a solid-state reaction. Colossal dielectric permittivity (≥105) and a very low loss tangent (<1.5%) at 10 kHz were achieved. Furthermore, the ceramics exhibit excellent temperature stability with a broad operating temperature range (25–400 °C). The evolution of the concentrations of oxygen vacancies and reduced Ti3+ was estimated by the XPS. Defect dipole complexes, coupled between the negatively and positively charged defects, are responsible for the observed huge dielectric permittivity. Temperature dependence of dc conductivity demonstrates that the stability of the defect dipole complexes matches the temperature range of stable dielectric properties. The result bridges a relationship between defect dipoles and dielectric behavior to understand the huge permittivity response and low loss mechanism.

Origin of Colossal Dielectric Permittivity in (Nb + Ga) Co-Doped TiO2 Single Crystals

Origin of Colossal Dielectric Permittivity in (Nb + Ga) Co-Doped TiO₂ Single Crystals

Colossal dielectric permittivity and high energy storage efficiency in barium strontium titanate ceramics co-doped with bismuth and lithium

The development of energy storage devices in lead-free perovskite materials is critically important in addressing the environmental issues of perovskite lead. In this article, for the first time, lead-free (Ba0.60Sr0.40)(1−x)(Bi,Li) x TiO3, abbreviated as (BST6:BLx%); (0%⩽ x ⩽ 8%) ceramics, have been successively synthesized via the conventional solid-state reaction method. The structural evolution, dielectric and energy storage properties, as functions of co-doping levels, were systematically studied by x-ray diffraction, x-ray photoelectron spectroscopy (XPS), high-resolution transmission electron microscopy, scanning electron microscopy, impedance analyzer, and a Radiant Precision Premier II Analyzer. It was found that a small amount of co-dopants induced a colossal permittivity (CP) (over 105) with low loss (<0.1), a maximum energy storage density of 0.3856 J cm−3 with a BDS of ∼100 kV cm−1, and an efficiency of over 90%. The defects and chemical state of the elements contained in the material’s surface were investigated using XPS. In conjunction with the results of XPS and complex impedance studies, the mechanism of massive permittivity was interpreted based on a defect-dipole model. We believe that BST6:BLx% ceramics, as CP and high energy storage efficiency materials, might be considered a promising candidate for high energy storage applications.

Dipole relaxation process and giant dielectric permittivity in Eu3+-doped CdMoO4 single crystal

Single crystal of Eu3+-doped cadmium molybdate (Cd0.9268▯0.0244Eu0.0488MoO4, where ▯ denotes cationic vacancies) has been successfully grown by the Czochralski method in air and under 1 MPa. X-ray diffraction analysis indicates that as-grown single crystal exhibits tetragonal scheelite-type structure (a = b = 5.16188(14) Å; c = 11.2080(5) Å; space group I41/a). Eu3+ ions do not show long-range order and they are randomly distributed in CdMoO4 framework substituting Cd2+ ones. UV–vis diffuse reflectance measurements revealed very close optical band gap (Eg) values, i.e. ∼1.74 eV along [100] and [001] crystallographic directions that are twice smaller than Eg of microcrystalline pure CdMoO4 as well as powder Eu3+-doped single crystal. Magnetic and electrical studies of Eu3+-doped cadmium molybdate single crystal showed a paramagnetic and n-type semiconducting behaviour with the metal-insulator transition above 350 K along both crystallographic directions. Dielectric results analysis using the Cole-Cole fit function revealed that the dipole relaxation process has different time scale depending on the crystallographic direction and exhibits Arrhenius temperature dependence for both studied directions. This fact is accompanied by the colossal dielectric permittivity with εr > 8⋅103. The above results are considered in the framework of narrow europium multiplets of energy comparable to thermal energy.

Jahn-Teller assisted polaronic electron hopping in LiCuNb3O9

The role of A-sited elements in double perovskite colossal dielectric LiCuNb3O9 has been analyzed by replacing the Cu ions with Li ions. Structural analysis revealed the presence of Jahn-Teller effect because of the Cu ions. Two thermally activated relaxations have been observed: the lower temperature one has been assigned to be a polaronic relaxation following Mott variable-range-hopping mechanism. Impedance analysis and humidity sensitive test proved that the higher temperature one is a Maxwell-Wagner relaxation. Our work highlights that the polaronic hopping is responsible for the colossal dielectric permittivity behavior of LiCuNb3O9.

Tailorable Dielectric Performance of Niobium‐Modified Poly(hydridomethylsiloxane) Precursor‐Derived Ceramic Nanocomposites

The low‐frequency dielectric behavior of in situ crystallized and stabilized nanocrystalline t‐NbO2 in amorphous silicon oxycarbide (SiOC) ceramic nanocomposites derived from niobium‐modified poly(hydridomethylsiloxane) (PHMS) is reported. Commercially available PHMS is modified using Nb(OC2H5)5 via chemical and mechanical mixing route. It is observed that the synthesis route and heat‐treatment temperatures significantly affect the crystallization of the ceramic phases, where c‐NbC and t‐NbO2 in amorphous SiOC are formed through chemical and mechanical modification route, respectively. The variation in dielectric permittivity and loss at room temperature with respect to ceramic phases is comprehensively investigated. In contrast to amorphous SiOC ceramics derived from PHMS (ε′ = 100.0 at 1 Hz), t‐NbO2 in amorphous SiOC ceramic exhibits colossal dielectric permittivity (ε′ = 5.0 × 105 at 1 Hz) with low loss (tan δ &lt; 3.0). This is attributed to an interfacial charge polarization and in situ growth of insulator/semiconductor/insulator ceramic phases in amorphous SiOC ceramic nanocomposites.

Significantly improved dielectric properties of TiO2 ceramics through acceptor-doping and Ar/H2 annealing

The acceptor-doped rutile TiO2 ceramics, x mol% M2O3-(1-x) mol% TiO2 (M = Al3+, Ga3+, and In3+), were prepared by solid state reaction method. The influence of Ar/H2 annealing on the structural and dielectric properties of the ceramics were systematically investigated. Our results reveal that the dielectric properties of the ceramics can be significantly improved by the Ar/H2 annealing. Ga3+ is found to be the most suitable dopant with the best doping level of 5 mol%. Excellent dielectric properties of colossal and flat dielectric permittivity (~1.2 × 105 (@1 kHz and 25 °C), low dielectric loss (~0.1), and good frequency stability were achieved over the temperature range of -70–150 °C in the Ar/H2-annealed 5 mol% Ga2O3-95 mol% TiO2 ceramic. This approach of acceptor-doping and Ar/H2 annealing leads to two thermally activated relaxations in the sample. The low-temperature relaxation is argued to be a Maxwell-Wagner relaxation caused by frozen electrons, while the high-temperature relaxation is a glass-transition-like relaxation associated with the freezing process of the electrons. This work highlights that engineering low-temperature Maxwell-Wagner relaxation paves a new way other than the frequently used acceptor-donor dual doping to design superior dielectric properties in the TiO2 system.

Double pentavalent (Sb5+, Nb5+) and trivalent (Sm3+, Y3+) co-doped Ti0.9Zr0.1O2 colossal dielectric permittivity multilayer ceramics for the miniaturization of the next-generation electronics

Materials with colossal dielectric permittivity (CP) are in the focus of interest for the development of miniaturization and integration of electronic components. Despite the extensive study of these new classes of co-doped TiO2 CP materials, the preparation of multilayer ceramics using this kind of CP materials is still challenging work. Here, we synthesize a series of (Sb5+, Nb5+) and (Sm3+, Y3+) co-doped Ti0.9Zr0.1O2 ceramics (SNSYTZO) through the conventional solid-state reaction method. XRD spectrum identifies that ceramics under x = 0.04 show a perfect rutile phase with the tetragonal crystal structure; however, minor brookite orthorhombic crystal structure appears when x > 0.04. FESEM images show the prepared ceramics have excellent densification and low porosity. Dielectric, modulus, and impedance spectrum are systematically explored the underlying CP mechanism and compared with each other to find the optimal materials composition to prepare further multilayer ceramics, which is fabricated by the industrial tape casting method. FESEM, together with surface element mapping, indicates that all doping elements are homogeneously distributed. Also, we investigate the dielectric response without/with DC bias. This work sheds light on a promising feasible route to prepare the miniaturization of the next-generation electronics via a large scale industrial tape casting method.

Colossal dielectric permittivity in co-doping SrTiO3 ceramics by Nb and Mg

(Mg + Nb) co-doped SrTiO3 dielectric ceramics were prepared using a solid-phase synthesis method to investigate dielectric properties as a function of doping contents, temperature, and frequency. A very low dielectric loss (0.0354, at 1 kHz) and colossal permittivity (21026, at 1 kHz) were observed in Sr(Mg1/3Nb2/3)xTi1-xO3 (x = 5%) at room temperature. The dielectric properties showed good frequency stability while three significant dielectric relaxations appear over a wide temperature range: −155 °C–500 °C. Combining with the X-ray photoelectron spectroscopy results, the mechanism of the colossal permittivity in our samples was discussed according to electron-pinned defect-dipoles model.

Colossal dielectric permittivity of Nylon-6 matrix-based composites with nano-TiO2 fillers

Herein, the nanocomposite films of Nylon-6 with reinforced nano-TiO2 were explored for their charge storage capacity. The high dielectric constant (e) of TiO2, along with its compatibility with Nylon-6, formed the basis for the present study. TiO2 nanoparticles were synthesized initially using hydrothermal technique. The microscopic uniformity and anatase-phase purity of the TiO2 nanoparticles were confirmed with the help of morphological and structural investigations. The effect of weight fraction of TiO2 in Nylon-6 was investigated to understand the robustness of the fabricated nanocomposites. The composite films with 5, 10 and 20 wt% of TiO2 in Nylon-6 matrix were prepared, and their dielectric behavior was explored by fabricating capacitors with parallel plate architecture. The composite film with 20 wt% TiO2 showed the highest dielectric parameters. The nanocomposite films have the exceptional dielectric quality with e ~ 124 and low dielectric loss of 0.51 at 1 kHz. The colossal dielectric nature along with minimum sophistication in the film fabrication process makes the present nanocomposite to be a potential candidate for the various electronic devices.

Electron-pinned defect dipoles in (Li, Al) co-doped ZnO ceramics with colossal dielectric permittivity

The colossal dielectric constant and relatively low dielectric loss (εr = 9862 and tan δ = 0.159) in ZnO ceramics have been achieved via acceptor and donor co-doping method.

Structural, magnetic and electronic properties of Ti-doped BaFeO3-δ exhibiting colossal dielectric permittivity

We report a systematical investigation of the structural, magnetic, electronic, and dielectric properties of BaFe1-xTixO3-δ (x = 0.05, 0.10, 0.15 and 0.20) samples synthesized via the solid-state reaction method. Rietveld refinement using a combination of room-temperature X-ray (XRD) and neutron powder diffraction (NPD) data confirms single phases with a 6H-type structure for all the samples. X-ray absorption spectroscopy (XAS) study reveals a coexistence of Fe3+ and Fe4+, whose ratio remains almost unchanged with increasing Ti concentration. Magnetization measurements reveal a low-temperature inhomogeneous magnetic state with coexisting ferromagnetic (FM), AFM clusters and a paramagnetic phase. Moreover, magnetization of x = 0.10 shows a pinched hysteresis loop behavior, suggesting the coexistence of hard and soft FM phases in samples with high Ti concentrations. Low-temperature NPD measurements also confirm the absence of any long-range magnetic order in the samples. A colossal dielectric permittivity and two relaxation processes are observed for most of the studied samples. There is a change in electric conduction mechanism from the small polaron hopping to the Mott's variable-range hopping with increasing Ti concentration.

Colossal dielectric permittivity and mechanism of AC conduction in bulk delafossite CuFeO2

We report structural, dielectric, and ac conductivity studies of CuFeO2, a material that belongs to the delafossite family. X-ray diffraction, X-ray absorption near edge structure (XANES), and impedance studies were carried out in order to investigate the structural and dielectric properties of the system. XANES measurement suggests that Fe present in the sample is in a mixed valence state. Dielectric properties measured at a temperature range of 84–450 K exhibit colossal dielectric permittivity with clearly distinguishable grain and grain boundary contributions. It has been found that both short-range and long-range motions of charge carriers are present in the sample, with the short-range motion dominating at low temperatures and long-range motion dominating at high temperatures. It has also been observed that the conduction in the sample is dominated by the conduction through the grain boundaries.

Colossal dielectric permittivity in (Al+Nb) co-doped Ba0.4Sr0.6TiO3 ceramics

Abstract Stimulated by the outstanding colossal permittivity behavior achieved in trivalent and pentavalent cations co-doped rutile TiO2 ceramics, the co-doping effects on the dielectric behavior of Ba0.4Sr0.6TiO3 ceramics were further explored. In this work, (Al + Nb) co-doped Ba0.4Sr0.6TiO3 ceramics were synthesized via a standard solid state ceramic route. The structural evolution was analyzed using X-ray diffraction patterns and Raman spectra. Dense microstructures with no apparent change of grain morphology were observed from the scanning electron microscopy. A huge enhancement of dielectric permittivity was obtained with 1 mol% (Al + Nb) doping and excellent dielectric performances (er ∼ 20,000, tanδ ∼ 0.06 at 1 kHz) were achieved after further heat treatment. The formation of electron pinned defect dipoles localized in grains may account for the optimization of dielectric behaviors and the corresponding chemical valence states were confirmed from the XPS results.

Microstructure and electric response of Li,Sn co-doped NiO ceramics

Phase composition, microstructure and electric response of Li0.05SnxNi0.95 - xO (x = 0, 0.025, 0.05, 0.1) ceramics were systematically investigated. Colossal dielectric permittivity (&gt;5000) is observed in the frequency range of 102-105 Hz at room temperature which becomes highly frequency-independent with increasing temperature. Secondary Sn-rich phase is detected in the grain boundary regions and it has a remarkable influence on the dielectric properties. Impedance spectroscopy analysis demonstrates that the microstructure is electrically heterogeneous, consisting of semiconducting grain and insulating grain boundary. Defect dipoles or polyvalent cations induced at high temperature may activate an electron hopping process under electric field, resulting in the enhancements of grain conductivity and polarization effect. This behaviour should be considered as the origin of the observed dielectric response.

A novel approach to study the conductivity behavior of CaCu3Ti4O12 using scanning probe microscopy technique

Abstract

An approach for correlating electrically heterogeneous structure to enhanced dielectric properties of Sr and Zn co-substituted CaCu3Ti4O12 ceramics

In the present work, the most pristine as well as strontium (Sr) and zinc (Zn) modified Calcium copper titanate ceramics having formula Ca0.95Sr0.05Cu3Ti4-xZnxO12 (x = 0.01, 0.025, 0.05 & 0.10) were synthesized by the solid state reaction method. X-ray diffraction pattern and Raman analysis confirmed the single phase formation of the samples. Detailed structural information was carried out by Rietveld refinement, analysis of X-ray data. Microstructure investigation revealed that the grain development of the doped ceramics was controlled by dopant (Zn) ions due to solute drag effect. Impedance spectroscopy was used to investigate the contribution of grains, grain boundaries and electrode interface effect to the dielectric response. Dielectric parameters observed to be improved for higher Zn/Sr ratio in studied compositions. The Ca0.95Sr0.05Cu3Ti3.90Zn0.10O12 ceramic composition shows a colossal dielectric permittivity of ∼37,788 and loss ∼0.049, which are stable within a broad frequency region. Reduced tanδ over a broad range of frequency was well ascribed to the highly insulating grain boundaries. The giant dielectric properties of the system were found to be in accordance with Internal Barrier Layer Capacitance (IBLC) model and correlated to their electrically heterogeneous structure.

Wide range dielectric and infrared spectroscopy of (Nb+In) co-doped rutile ceramics

The dielectric response of ceramics of co-doped rutile $\mathrm{T}{\mathrm{i}}_{1\text{\ensuremath{-}}x}{(\mathrm{N}{\mathrm{b}}_{0.5}\mathrm{I}{\mathrm{n}}_{0.5})}_{x}{\mathrm{O}}_{2}$ has been measured via a combination of impedance, high-frequency coaxial, terahertz transmission, and infrared reflectivity spectroscopies spanning 15 decades of frequency between 0.1 Hz and 240 THz. It is argued that the colossal dielectric permittivity reported by Hu et al. [Hu et al., Nat. Mater. 12, 821 (2013)] has the same explanation as in the original colossal permittivity material $\mathrm{CaC}{\mathrm{u}}_{3}\mathrm{Ti}{\mathrm{O}}_{4}{\mathrm{O}}_{12}$ (CCTO), namely, a combination of the internal barrier layer capacitor (IBLC) and the surface barrier layer capacitor (SBLC) effects. The IBLC effect is caused by a microstructure consisting of insulating grain boundaries (thickness \ensuremath{\sim}1 nm and conductivity of $\ensuremath{\sim}{10}^{\ensuremath{-}6}\phantom{\rule{0.16em}{0ex}}\mathrm{S}/\mathrm{cm})$ surrounding interior regions of bulk conductivity approximately equal to ${10}^{\ensuremath{-}1}\phantom{\rule{0.16em}{0ex}}\mathrm{S}/\mathrm{cm}$. The SBLC effect is the result of a depletion layer adjacent to the contacts approximately 100 nm thick with conductivity of $5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}7}\phantom{\rule{0.16em}{0ex}}\mathrm{S}/\mathrm{cm}$. The SBLC and IBLC effects give rise to dielectric relaxations in low-frequency and radiofrequency regions, respectively. The temperature dependence of both relaxation rates measured down to 20 K is thermally activated. No separate absorption process has been observed that could be linked to giant defect dipoles. Infrared spectroscopy has revealed four weak defect-related modes at frequencies close to the Raman mode frequencies of rutile, activated in the infrared through a symmetry-breaking process. Co-doping produces a significant loss in the partial spectral weight between 75 and $350\phantom{\rule{0.16em}{0ex}}\mathrm{c}{\mathrm{m}}^{\ensuremath{-}1}$ associated with the lowest transverse optical mode, which softens on cooling. The loss in its spectral weight corresponds to the gain in near-infrared spectral weight, previously assigned to small polaron absorption.

Colossal dielectric response in Ba1.5Sr1.5Co2Fe24O41 ceramics at high-temperature

Polycrystalline Ba1.5Sr1.5Co2Fe24O41 ceramics were prepared by the sol–gel method with clear grains and grain boundaries having been identified by the scanning electron microscopy. High-temperature colossal dielectric response has been observed and studied through a series of dielectric and impedance measurements. The electrode effect was also studied and the measurement findings reveal that the colossal dielectric permittivity at low frequency is ascribed to the extrinsic effect of Maxwell Wagner polarization. Dielectric relaxation was identified and investigated by the impedance spectra, which is attributed to the thermally activated model. The complex impedance data is simulated with an equivalent electric circuit and the result suggests that the electric response originates from both the grains and grain boundaries. The activation energies of the grains and grain boundaries are calculated which are 0.62 and 0.67 eV, respectively. The comparable activation energies obtained from the complex impedance spectra and DC conductivity indicates that the relaxation may result from the conduction process. Besides, scaling behaviors are observed below 550 K suggesting that the relaxation time is temperature independent.

Conductivity-permittivity relations in oxygen deficient CaCu3Ti4O12

The correlation between conductance, capacitance and oxygen content is discussed in the colossal dielectric permittivity perovskite oxide CaCu3Ti4O12. We found an unusual positive conductivity-permittivity relation which is very sensitive to the oxygen content. In particular, we ascribe the oxygen content sensitivity of both the capacitance and the conductance to a repositioning of charges on oxygen vacancy related defects and/or on the migration of the defects themselves. We find that in the charge repositioning process a Jonscher type of global conduction is accompanied by a Debye-type local electronic relaxation in and between the boundaries of a specific grain. A closer investigation of these processes suggest that the local polaronic relaxation of charges on oxygen vacancy related defects is mainly responsible for the large dielectric constant of CaCu3Ti4O12 and also for the ac conduction at low to medium temperatures.