Colossal Dielectric Permittivity Research Articles

Role of mixed oxidant and controlled oxygen partial pressure heat treatment to regulate the dielectric properties and resistivity of SrTiO3-based CP ceramics

Sr0.99La0.01TiO3 (SLT10) colossal permittivity (CP) ceramic materials were synthesized using solid phase method and secondary heat treated using mixed oxidant 35%Bi2O3–10%Al2O3–20%MgO–25%CuO–10%SiO2 oxidant. The heat treatment atmospheres were chosen as O2, air, and Ar to correspond to different oxygen partial pressures. The dielectric properties of the Sr0.99La0.01TiO3-Percolated (SLT10-P) ceramics were investigated, and the contribution of the oxidant to the resistivity enhancement was verified by complex impedance spectroscopy and DC resistivity tests. Excellent dielectric properties were obtained for SLT10-P Air ceramic sample (16543 for dielectric permittivity and 0.016 for loss tangent), and the resistivity was increased from 2.13 × 108 Ω cm (SLT10) to 1.23 × 1011 Ω cm (SLT10-P Air). The resistance degradation mechanism of SLT10-P ceramics and oxygen vacancy migration in the process of resistance degradation were studied by using resistance monitoring device and thermally stimulated depolarization currents (TSDC) test. The introduction of oxidant optimizes the temperature stability and resistivity of SLT10 ceramics, but it will lead to the decrease of dielectric permittivity. The atmosphere of heat treatment changed the concentration of oxygen vacancy in ceramics. When SLT10-P O2 was treated in O2 atmosphere, the concentration of oxygen vacancy in ceramics decreased, which led to the decrease of dielectric permittivity and the increase of grain boundary resistance. For SLT10-P Ar ceramic, more oxygen vacancies and free electrons are induced by low oxygen partial pressure heat treatment, which enhances the dipole effect of electron pinning defects and leads to colossal dielectric permittivity, but high concentration of oxygen vacancies will affect the resistance decline. In SLT10-P Air ceramic, the coexistence of colossal permittivity and low loss tangent and high resistance is realized.

Defect engineering in rare-earth-doped SrTiO3 ceramics: Route to colossal capacitance material up to X9R capacitor standard

With the advent of the electronic information era, capacitors have become a hot research topic due to their economic and strategic significance. Such microelectronic components play an irreplaceable role in important fields such as scientific research and military industries. Therefore, there is an urgent need to develop dielectric materials capable of withstanding more demanding conditions. In this work, a defect engineering method was incorporating Tm3+ rare earth ions into strontium titanate were proposed, resulting in a colossal dielectric permittivity, low dielectric loss, and excellent frequency and temperature stability. For the sample with x=0.01, the dielectric permittivity exceeds 345,804, the dielectric loss is below 0.011, and the dielectric permittivity variation within the temperature range from −55–200°C is less than 15%, which meets the ELA X9R capacitor standard (X: −55 °C, 9: +200 °C, R: Δεr ≤ ± 15%). The excellent performance is ascribed to the electron pinning defect dipole effect (EPDD) and internal barrier layer capacitor effect (IBLC), which is verified by XPS and impedance spectra. A deeper understanding of these mechanisms could help to reveal the origin of the colossal capacitance and thus contribute to the design of materials with colossal capacitance.

X9R-type SrTiO3 based ceramics with colossal dielectric permittivity and low loss derived from defect engineering and high-energy ball milling

The miniaturization of electronic components has become a megatrend in the future, making colossal dielectric permittivity materials receive unprecedented attention. In this work, we proposed a universal route to achieve colossal dielectric permittivity, low loss factor and excellent dielectric temperature stability in rare earth doped perovskite oxide SrTiO3. Sm doped SrTiO3 ceramics prepared by high-energy ball milling exhibit ultrahigh dielectric permittivity 441,543, low loss factor 0.02, good dielectric temperature stability (<15 %) in the temperature range of −55–200 °C, and very high resistance 109Ω, which meets the EIA X9R standard, XPS and impedance spectra indicate that the electron-pinned defect-dipoles effect is the origin of colossal dielectric permittivity and low loss factor. This work shows that Sm-doped SrTiO3 activated by high-energy ball milling has broad prospects in the applications of thermally-stable miniaturized capacitors.

A review on structure–property relationships in dielectric ceramics using high‐entropy compositional strategies

AbstractHigh‐entropy strategy is a design that uses multiple elements to increase configurational entropy. As an emerging research field, high‐entropy was originally applied to metals, but it has shown great potential in inorganic nonmetallic materials. Since the first discovery of colossal dielectric permittivity in high‐entropy ceramics, it indicates that the high‐entropy strategy is feasible in dielectric ceramics. The multi‐ion solid solution will bring a broader space for the material structure and property tailoring. With the research of domestic and foreign scholars in high‐entropy dielectrics, we believe that entropic engineering can effectively regulate dielectric properties. The review paper explores the potential of the high‐entropy strategy in dielectric ceramics. It provides a detailed overview of the structural properties and the potential benefits of utilizing high‐entropy materials in dielectric ceramics. The review also covers the current research advancements in the field and provides insights into future directions for further development of high‐performance dielectric ceramics.

Hopping conduction of localized polarons with scaling behaviour in ceramic composite (YCrO3)1 -x - (CoFe1.6Cr0.4O4)x

The percolative (YCrO3)1 -x – (CoFe1.6Cr0.4O4)x (x = 0.3, 0.5, 0.7, 1.0), ceramic composite belongs to a family of materials that exhibit colossal dielectric permittivity. Our fundamental interests lie in the investigation of the conduction mechanism of the composite from both microscopic and macroscopic perspectives. Here, all three ceramic composites have been chosen for a comparative study containing CFCO above fc, near fc, and below fc. The electrical conductivity of the composite follows Mott’s variable range-hopping model in the temperature range of 300 – 500 K, indicating domination of this model in conduction of localized polarons in the electrical behaviour. Parameters, including the dc conductivity, hopping, most probable hopping range, the activation energies involved in the said model, the density of localized states at the Fermi level, and relaxation were obtained and analyzed. Scaling behaviors of conductivity and imaginary part of complex impedance were investigated, showing a temperature-independent distribution of relaxation times. By looking at the impedance data at a variety of temperatures, semiconducting behaviour is demonstrated, which has been modelled by an equivalent circuit model that incorporates grain and grain boundary responses. The ferroelectric nature of the samples resembled lossy characteristics due to the presence of the CFCO phase. The correlation between conductivity and colossal apparent permittivity helps in better understand the conduction mechanism in ceramic composites comprising semiconducting and insulating phases.

Ge-doping effect on the optical, magnetic, and dielectric properties of CuBO2 delafossite oxides

In this work, we report the microstructural, optical, magnetic, and dielectric properties of CuB1-xGexO2 (x = 0.00, 0.01, and 0.03) prepared using a solid-state reaction method. These properties were investigated using several techniques, including X-ray diffraction (XRD), scanning electron microscopy (SEM), UV–visible spectroscopy, vibrating sample magnetometry (VSM), and impedance analysis. We found that all samples had a main crystal structure of the 3 R delafossite (space group R-3 m). For the doped samples (x = 0.01 and 0.03), a secondary phase of CuGeO3 was observed. All the powder samples had an average particle size of approximately 300 nm with an irregular hexagonal shape. These samples showed a strong absorbance peak at a wavelength centered at 250 nm, which indicated a direct optical bandgap in range of 2.91–2.96 eV. Ferromagnetism was achieved in the Ge-doped samples at 50 K. Finally, colossal dielectric permittivity was observed in both undoped and Ge-doped ceramic samples.

Colossal Dielectric Permittivity in Sb/Gd Codoped Rutile TiO2 Nanoparticles Generated by Hydrogen Reduction

Abstract Ceramic TiO2 nano particles codoped with Sb/Gd ions were synthesized by a hydrothermal decomposition-precipitation technique. Some of the synthesized samples were hydrogenated at ∼550°C. The samples were characterized by investigating their structural, optical, and electrical properties by X-ray diffraction, diffuse reflection spectroscopy, and dielectric measurements, respectively. It was observed that the 3 %-Sb/Gd ionic codoping induces the growth of the rutile TiO2 phase. The different types of ionic doping of Sb5+ and Gd3+ into TiO2 nanograins found expectation to arrange core/shell sample construction that can be used to produce almost colossal permittivity material. However, the dielectric measurements showed relatively weak permittivity of order ∼370 at 1 kHz. Hydrogenation was used to create colossal permittivity, and the results show a significant increase by ∼6.63 times at 1 kHz. This result is important from the point of view of studying the influence of hydrogenation on the dielectric properties of transparent conducting oxides. The created colossal permittivity was explained within the framework of the core/shell model and doping mechanisms. Thus, the hydrogen species accumulation on the crystallite boundaries supports the creation of core/shell and colossal permittivity in addition to the generation of itinerant electrons. Such important results will be useful for future work and will support this field of research.

High permittivity and low dielectric loss of the (Ca0.9Sr0.1)1-xLa2x/3Cu3Ti4O12 ceramics

In this work, we have systematically studied the effects of La3+/Sr2+ dopants on the crystal structure, microstructure, dielectric response and electrical properties of (Ca0.9Sr0.1)1-xLa2x/3Cu3Ti4O12 (x = 0, 0.025, 0.05 and 0.075) ceramics. XRD results show that the lattice parameter increases with the increase in the La3+ content. SEM micrographs illustrate that a small amount added of La3+ can reduce the grain size of CCTO during sintering. With increasing La3+ content, the grains grow larger. Dielectric measurements indicated that all doped samples synthesized by the solid-state reaction exhibit giant dielectric constants ε'>104 over a large frequency range (10 Hz to 1 MHz) and at any temperature below 600 K. In particular, the ceramic with x = 0.05 exhibits a colossal dielectric permittivity ∼5.49 × 104; which increases by about 50% compared to that of the undoped ceramic. In addition, the doped ceramic also presents a low dielectric loss ∼ 0.08 at 20 °C and 0.6 kHz. The giant dielectric properties of these samples can be explained by the (IBLC) model.

New insight into the colossal dielectric permittivity and AC conductivity behavior of polycrystalline non-ferroelectric ceramics

The correlation of polarization with AC conductivity behavior of polycrystalline non-ferroelectric ceramics is more satisfied to be interpreted by three zones indicated in permittivity and AC conductivity spectra. These three zones concerning the dielectric and conductivity processes governing the response to an AC field have been identified in terms of the cluster model within the framework of percolation theory. Colossal dielectric permittivity of non-ferroelectric materials can be attributed to hopping polarization aligned via developing percolation clusters with high electron concentrations. The physical origin of the correlation between dielectric permittivity and AC conductivity of polycrystalline ceramics with respect to the effect of grain boundary has been clarified.

Colossal dielectric permittivity in CuCrO2 ceramics

CuCrO2 ceramics were prepared by solid-state reaction method. Low-temperature (10–320 K) dielectric properties were investigated in the frequency range of 102–106 Hz. Colossal dielectric constant behavior composed of two thermally activated relaxations was observed. The low-temperature relaxation (R1) occurring around 125 K with an activation energy of 0.21 eV was ascribed to be a dipolar relaxation caused by defect dipoles of OHO•−Cr3+. The high-temperature relaxation (R2) appearing around 200 K with an activation energy of 0.26 eV was argued to be a Maxwell-Wagner relaxation originating from humidity sensitivity.

Eff ects of Cr Doping on Physical Properties of CuBO2 Delafossite Oxide

In this research work, CuB1−xCrxO2 (x = 0.00, 0.01, 0.03, 0.05, and 0.07) were synthesized by using a conventional solid-state reaction method. The effects of Cr concentration on its microstructure, optical, magnetic, and dielectric properties were investigated. X-ray diffraction (XRD) results revealed the crystal structure of all samples belongs to the R-3m delafossite structure. Besides, a second phase CuCrO2 appeared in a high Cr content sample. Scanning electron microscope (SEM) indicated that particle size of samples was about 300 nm and slightly increased with increasing the Cr content. The optical properties measured by UV-visible spectroscopy showed the absorbance peak at ~250 nm. The corresponding direct optical band gap was about 2.90 eV. The magnetic hysteresis curve measurements of all samples revealed the paramagnetic behavior at room temperature. Noticeably, the Cr-doped samples (x = 0.01−0.07) exhibited as a ferromagnetic behavior at 50 K. Furthermore, the zero-fi eld-cooling magnetization of the Cr-doped samples shows a ferromagnetic transition temperature at ~130K. Finally, the dielectric measurement of all samples shows the colossal dielectric permittivity.

Influence of Feldspar Addition on the Properties of CaCu&lt;sub&gt;3&lt;/sub&gt;Ti&lt;sub&gt;4&lt;/sub&gt;O&lt;sub&gt;12&lt;/sub&gt; Ceramic

The colossal dielectric permittivity of calcium copper titanate (CaCu3Ti4O12, CCTO) provides a vast potential in miniaturizing electronic devices but become limited due to high dielectric loss. Hence, feldspar was introduced to reduce the dielectric loss and fill in the air gap of CCTO during the sintering process. The CCTO powder was prepared by the solid-state reaction method. The study focused on characterizing pure and feldspar added CCTO properties on phase formation and dielectric properties. The raw materials were weighed, followed by stoichiometric ratios for pure CCTO. While the addition of feldspar was added using a weight percentage ratio of 1%, 3%, 5%, 7% and 10%. The mixed powders were ball mixed for 24 hours using dry mixing. The mixed powder was calcined at 900°C for 12 hours and then pressed into a pellet with 6 mm diameter, then sintered at 1040°C for 10 hours. The X-ray Diffraction (XRD) machine and impedance analyzer were utilized to observe the phase formation and dielectric properties of the samples prepared. A single phase of CCTO was obtained after the sintering process except for pure CCTO and 1wt% of feldspar addition, and it still has remaining CuO in the ceramic. Even though feldspar can reduce the dielectric loss of the CCTO from 0.6 (pure CCTO) to 0.4 (10 wt%) at 1 MHz, it also hard to maintain the high dielectric constant. The dielectric constant of 1wt% of feldspar addition was recorded the highest value, up to 4000 at 1 MHz, while the lowest dielectric constant owned by 10wt% of feldspar addition, ~700 at 1 MHz.

New Insight into the Colossal Dielectric Permittivity and AC Conductivity Behavior of Polycrystalline Non-Ferroelectric Ceramics

New Insight into the Colossal Dielectric Permittivity and AC Conductivity Behavior of Polycrystalline Non-Ferroelectric Ceramics

Unusual semiconductor-metal-semiconductor transitions in magnetite Fe3O4 nanoparticles.

Magnetite (Fe3O4) nanoparticles were successfully prepared by a co-precipitation method. Rietveld refinement on the X-ray diffraction pattern confirmed the development of a single-phase cubic spinel structure with space group Fd3̄m. However, 57Fe Mössbauer spectroscopy suggested the presence of Fe3+ and Fe2.5+ (mixed Fe3+ and Fe2+) ions at the tetrahedral and octahedral sites of the inverse spinel structure, respectively. Impedance spectroscopy measurements showed a discontinues variation in the temperature dependence of the sample's resistive behavior, indicating the appearance of semiconductor–metal–semiconductor like transitions between the temperature range of 293 and 373 K. A similar dual transition was also observed from the dielectric and conductivity measurements around the same temperature regions. The observed unusual transition is explained in term of the competitive effects among the hopping of localized/delocalized and short-range/long-range charge carriers present in the sample. Moreover, the prepared sample exhibits colossal dielectric permittivity (∼106), reduced tangent loss (∼0.2) and moderate conductivity (>10−6 S cm−1) values, making Fe3O4 nanoparticles a potential candidate for electromagnetic absorbing materials.

New Insight into Understanding the Colossal Dielectric Permittivity and AC Conductivity of Polycrystalline Ceramics

New Insight into Understanding the Colossal Dielectric Permittivity and AC Conductivity of Polycrystalline Ceramics

Colossal permittivity, electrical conductivity and ferromagnetic properties of pure TiO2: Mono and binary doping

Advanced doping and binary doping techniques can open pathways to enabling rapid manufacture of high desired materials and structures. Herein, enhanced room temperature ferromagnetism with colossal dielectric constant were detected in pure, Fe doped, (Fe, Mn) and (Fe, Ni) codoped TiO2. High purity TiO2, Ti0.98Fe0.02O2, Ti0.96Fe0.02Mn0.02O2 and Ti0.96Fe0.02Ni0.02O2 compositions were synthesized by means of coprecipitation method. The XRD crystallographic planes of TiO2 compositions showed that mixed phases of rutile and anatase TiO2 were formed with absence of any impurities phases related to Fe, Mn or Ni oxides. Wide visible light band gap energy until 497 nm was achieved in TiO2 due to incorporation of (Fe, Mn) ions. Parallel relation between doping, codoping and particles size reduction was observed which reflects the strong influence of dopants on the grains growth of TiO2. Interestingly, Ti0.98Fe0.02O2, Ti0.96Fe0.02Mn0.02O2 and Ti0.96Fe0.02Ni0.02O2 compositions exhibit room temperature ferromagnetic behavior with constructive retentivity and coercivity values. Colossal dielectric permittivity (> 103) of 2335, 2327, 1857 and 1746 was detected for TiO2, Ti0.98Fe0.02O2, Ti0.96Fe0.02Mn0.02O2 and Ti0.96Fe0.02Ni0.02O2 structures, respectively. All TiO2 compositions reveal semiconducting-temperature performance and the electrical conductivity was enhanced due to (Fe, Mn) and (Fe, Ni) codoping. At low frequencies, the room temperature electrical conductivity of Ti0.96Fe0.02Mn0.02O2 and Ti0.96Fe0.02Ni0.02O2 is higher than that of TiO2 and Ti0.98Fe0.02O2. It seems that the defects chemistry and the charge carriers concentration of the pure TiO2 sample were affected by (Fe, Mn) and (Fe, Ni) codoping.

Polaron assisted electrical transport and fertile field emission response in polycrystalline LiNi0.33Co0.33Mn0.33O2 with theoretical insight by density functional theory

Polycrystalline LiCo0.33Ni0.33Mn0.33O2 compounds were prepared via a sol-gel auto combustion synthesis route to examine its conduction mechanism with thermal assessment and a new window of its application as a field emitter is explored. The structural modules and molecular footmarks have been confirmed by XRD, Raman, FTIR, XPS and FESEM techniques. The Nyquist plots (Z′vs.Z′′) exhibits significant contribution of electrode solid interface effect with compared to intra and inter granular contribution. The variation of real and imaginary impedance, modulus, and conductivity spectra with thermal evolution is attributed with the creation of a quasi-particle called “polaron” and the migration of small polaron by tunneling/hopping creates localized state in high temperature. However, a weak crossover between small polaron hopping (SPH) and Mott’s variable range hopping (VRH) is observed near 323 K. The colossal dielectric permittivity (ɛr′)~5 × 106 is originated from inhomogeneous electronic conduction process in LiNi0.33Co0.33Mn0.33O2 due to the creation of absorption current in the flimsy grain boundary which leads to the stockpile of charge carriers in the external-electrode sample interface and induces Maxwell-Wagner electrode interfacial polarization. The exquisite field emission properties were discovered in LiNi0.33Co0.33Mn0.33O2 with low turn-on field@ 1 µA/cm2~2.75 V/µm and threshold field@ 10 µA/cm2~4.39 V/µm with field enhancement factor (β)~4251. The structural and electronic properties of LiNi0.33Co0.33Mn0.33O2 and the local work function (φ)~4.94 eV is computed employing the Density functional theory (DFT). It further supports the conduction mechanism due to self-trapping electrons and strong spin polarization of the O-2p state under applied electric field.

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.