Dielectric CaCu3Ti4O12 Research Articles

Improvement of dielectric properties and thermal stability of CaCu3Ti4.2O12 ceramics for X8R type capacitors via Co2+ doping

Work on giant dielectric CaCu3Ti4O12 (CCTO) ceramics has been continuously ongoing to obtain materials with a high dielectric constant (ε') and low dielectric loss tangent (tanδ) with both values stable over a wide temperature range. Various methods have been used to modify the materials, such as doping and co-doping with different transition metals at Ca or Cu sites, molar variation of metals (Cu, Ca and Ti), including altering in the methods and conditions of ceramic preparation. In general, the most common problem found in this type of research is that increasing ε' also increases tanδ. Thus, in this work, a one-step polymer pyrolysis (PP) procedure was used to obtain Co2+-doped CaCu3-xCoxTi4.2O12 (x = 0.00, 0.03, 0.05, and 0.07) powders. Then, all powders were sintered to obtain ceramics using two different sintering conditions, 1050 °C for 10 h and 1080 °C for 5 h. The influence of Co2+ ions and sintering conditions on the microstructure, dielectric properties and thermal stability of CaCu3Ti4.2O12 ceramics was investigated. Substitution of Co2+ ions at Cu sites can reduce tanδ values and increase ε' in samples with x = 0.03 and 0.05. However, the tanδ and ε' values were concurrently reduced for x = 0.07. Remarkably, a ceramic with x = 0.07 sintered at 1080 °C for 5 h exhibited very low tanδ(∼0.009) and colossal ε' (∼11551) at 1 kHz and 30 °C, over a broad temperature range (−60 to 150 °C), with stability of Δε' ≤ ±15 %. This ceramic is a suggested candidate material for X8R capacitors. Moreover, increasing the Co2+ doping level could significantly raise the nonlinear coefficient (α) of the ceramics from ∼ 3.48 to 34.30. Additionally, the very high Eb values of ceramics with x = 0.07 sintered at 1050 °C for 10 h and 1080 °C for 5 h were significantly increased by ∼26.34 and 17.45 times, respectively, compared to an undoped ceramic. A widened temperature range where Δε' ≤ ±15 % and tanδ < 0.05 in all ceramics with increasing Co2+ concentration is likely a result of increased grain boundary resistance.

Dielectric loss management by antimony (Sb) incorporation in giant dielectric CaCu3Ti4O12

The partial substitution of Sb5+ on the Ti site for giant dielectric constant material CaCu3Ti4O12 (CCTO) has been done in the present paper, and the effect of Sb substitution on the microstructural, dielectric and electrical property of the material is investigated. The main objective of this paper is to minimize high loss tangent (tan δ) which has restricted the practical applications of CCTO. XRD analysis carried out on the as-synthesized powders confirms formation of single phase material accompanied by dopant-induced lattice constant shrinkage. Scanning electron microscope images demonstrate that the grain size of sintered ceramic samples decreases with the increasing Sb content. The dielectric response of sintered CaCu3Ti4−xSbxO12 samples studied by precision LCR meter suggests that Sb doping is an effective way for maintaining a high dielectric constant and low loss over a broad range in temperature and frequency. Room temperature complex impedance spectroscopy analysis suggests that all compounds are electrically heterogeneous consisting of semiconducting grains and insulating grain boundaries establishing internal barrier layer capacitance model. These results indicate that Sb-doped CCTO ceramics have a favorable prospect to be able to stimulate practical applications.

Balanced Performance Enhancements of a‐InGaZnO Thin Film Transistors by Using All‐Amorphous Dielectric Multilayers Sandwiching High‐k CaCu3Ti4O12

AbstractThe requirements of low power consumption and fast operation have necessitated the development of thin film transistors (TFTs) with exploration of new dielectric materials. Here, the unprecedented integration of high‐κ dielectric CaCu3Ti4O12 is reported, yielding significant enhancements in the performance of amorphous InGaZnO TFTs. Using a multilayer structured amorphous Al2O3/CaCu3Ti4O12/Al2O3 dielectric configuration, the performance of the transistors is greatly improved as highlighted with high saturation mobility (&gt;10 cm2 Vs−1), high on/off current ratio (3.8 × 107), low threshold voltage (≈0.51 V), and low subthreshold swing (≈0.45 V decade−1). The balanced performance enhancements are attributed to the lower density of interfacial/bulk trap states and sufficient band offsets.

Fabrication of miniaturized high bandwidth dielectric resonator on patch (DRoP) antenna using high dielectric CaCu3Ti4O12 nanoparticles

This paper deals with the performance evaluation of dielectric resonator on patch (DRoP) antenna using high dielectric CaCu3Ti4O12 nanoparticles (CCTO Nps) synthesized by low-temperature solution combustion method. X-ray diffraction pattern reveals that the optimum calcination temperature required for the formation of single phase CCTO Nps is 900 °C. Near-spherical morphology of CCTO Nps with nano size (∼100 nm) has been visualized using field emission scanning electron microscopic images. High-resolution transmission electron microscopic and selected area electron diffraction data reveal the cubic crystal system of CCTO Nps with preferential orientation of (220) plane. The low-frequency dielectric behaviors of CCTO Nps exhibit excellent properties like high dielectric constant (εr = 447) and low dielectric loss (tanδ = 0.42) at 30 °C. DRoP antenna fabricated using high dielectric CCTO Nps exhibits promising results such as wide bandwidth (540 MHz), good return loss (−21.23 dB) at 2.45 GHz and smaller in sizes (10.17 mm2), which is required for modern-day wireless communication systems.

Advanced FeTiNbO6/poly(vinylidene fluoride) composites with a high dielectric permittivity near the percolation threshold

FeTiNbO6 (denoted as FTN) is a recently discovered giant dielectric material with high Curie temperature (550 K). In this work, well dispersive FTN particles with mean particle size about 500 nm were synthesized by the improved solid-state reaction method. Using FTN particles as fillers and poly(vinylidene fluoride) (denoted as PVDF) polymer as matrix, multi-volume ratio (0%–60%) homogeneous ceramic/polymer composites have been prepared through a hot-pressing technology. At the same filling content, the FTN/PVDF composites display higher dielectric permittivity compared to the normal reported BaTiO3/PVDF composites, even larger than that of PVDF based composites using giant dielectric CaCu3Ti4O12 as filler. Especially, for 40 vol. % FTN/PVDF composites, the dielectric permittivity is as high as 181 measured at 100 Hz and 25 °C. Through the theoretical analysis correlated with structure evolution observation, it is deduced that the high dielectric performance originates from the combined effect of a variety of factors, such as giant dielectric semiconducting FTN particles, the micro-capacitor structure, and percolation phenomenon at appropriate volume fraction of FTN. Moreover, FTN/PVDF composites present strong dielectric relaxation behavior, which results from the superposition of the dielectric relaxation between PVDF and FTN. These flexible, easy processing FTN/PVDF composites with large dielectric permittivity values could find applications as new generational embedded capacitors.

ChemInform Abstract: A Novel Low Cost Non‐aqueous Chemical Route for Giant Dielectric Constant CaCu3Ti4O12 Ceramic.

AbstractHighly crystalline giant dielectric CaCu3Ti4O12 (CCTO) is prepared by combustion of a stoichiometric Me‐O‐(CH2)2‐OH solution of the metal nitrates and inexpensive TiO2 followed by sintering of the obtained CCTO powder (1050 °C, 30 h).

Molecular Kinetic Based Dielectric Polarization in Sol-Gel Derived Nanocrystalline CaCu&lt;sub&gt;3&lt;/sub&gt;Ti&lt;sub&gt;4&lt;/sub&gt;O&lt;sub&gt;12&lt;/sub&gt;

Nano-sized powders of dielectric CaCu3Ti4O12 was synthesized by sol-gel reaction route. The powders are calcined at 700 °C and sintered at 1000 °C. The calcined powders diameter is in the range of 50 - 150 nm. Structural studies were carried out using the XRD, HRTEM and SEM. Frequency dependent dielectric properties were studied within the range of 20 Hz to 5 MHz. Molecular kinetics associated with dielectric relaxations is analyzed by Havriliak Negami function. It is found that the grain dipoles obey the Debye type of dielectric relaxation, while grain boundary dipoles follow the Cole-Cole type of dielectric relaxation. The observed grain and grain boundary dipole relaxation time are 6.598E-08 sec and 5.755E-04 sec, respectively.

Low dimensional fabrication of giant dielectric CaCu3Ti4O12 through soft e-beam lithography

We report low-dimensional fabrication of technologically important giant dielectric material CaCu3Ti4O12 (CCTO) using soft electron beam lithographic technique. Sol–gel precursor solution of CCTO was prepared using inorganic metal nitrates and Ti-isopropoxide. Employing the prepared precursor solution and e-beam lithographically fabricated resist mask CCTO dots with ∼200nm characteristic dimension were fabricated on platinized Si (111) substrate. Phase formation, chemical purity and crystalline nature of fabricated low dimensional structures were investigated with X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS) and selected area electron diffraction (SAED), respectively. Morphological investigations were carried out with the help of scanning electron microscopy (SEM) and transmission electron microscopy (TEM). This kind of solution based fabrication of patterned low-dimensional high dielectric architectures might get potential significance for cost-effective technological applications.

Microstructures and electrical properties of CaCu3Ti4O12thin films on Pt/TiO2/SiO2/Si substrates by pulsed laser deposition

Abstract

Epitaxial growth of dielectric CaCu3Ti4O12 thin films on (001) LaAlO3 by pulsed laser deposition

High dielectric CaCu3Ti4O12 (CCTO) thin films were epitaxially grown on (001) LaAlO3 (LAO) substrates by pulsed laser deposition. Microstructural studies by x-ray diffraction, pole figure measurements, and transmission electron microscopy show that the as-grown films are good single crystalline quality with an interface relationship of (001)CCTO//(001)LAO and [100]CCTO//[100]LAO. Dielectric property measurements show that the films have an extremely high dielectric constant with value of 10 000 at 1 MHz at room temperature. It is interesting to note that the twinned substrate results in the formation of twinning or dislocations inside the CCTO film.