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Due to the boom of the electronic information industry, dielectric ceramic materials are widely applied in passive components such as multilayer ceramic capacitors. In this article, Y2/3Cu3Ti4O12–TiO2 composite ceramics with outstanding dielectric properties (εr = 2.29 × 106 at 20 Hz, εr = 4.49×105 at 1 kHz) were successfully prepared by hydrothermal and in situ solid‐state methods. The minimum dielectric loss value (at 1 kHz) of the obtained composite ceramics is about 0.57. The experimental results show that Y2/3Cu3Ti4O12 has a composite perovskite structure with cation vacancies, which causes internal electron‐pinned defect‐dipole, and the easy entry of excessive titanium ions to produce donor defects. Meanwhile, the heterogeneous grains with a pomegranate‐like microstructure were observed in the prepared composite ceramics, and interfacial polarization between subgrain boundaries was substantiated by impedance analysis. The abundant weakly trapped electrons and more polarized interfaces formed by grain and subgrain boundaries are the primary sources of the excellent dielectric properties of composite ceramics. [ABSTRACT FROM AUTHOR]

The CCTO/SnO2 composite ceramics were fabricated by sintering at 1040°C for 8 h. The FESEM found that the grain size decreased sharply when the SnO2 addition amount reached 15 mol%. The dielectric spectra confirmed that the addition of SnO2 helps to improve the dielectric properties of CCTO, and the dielectric constants of 20 mol% SnO2 reached 1.74 × 106 and 4.2 × 105 at 20 Hz and 1 kHz, respectively. XPS found the coexistence of Cu+ and Ti3+ related to the defect compensation mechanism. Impedance spectroscopy confirms that the addition of SnO2 helps to improve the semiconductivity of CCTO, thereby enhancing the dielectric properties of CCTO. [ABSTRACT FROM AUTHOR]

CaCu3Ti4O12/CaTiO3/TiO2 (CCTO/CTO/TiO2) composite ceramics were fabricated by an in situ route and sintered at 1040 °C for 8 h. The micrographs of FESEM show that the ceramics are dense and delicate, with an average particle size of about 0.9–1.4 μm. XPS found the existence of Cu+ and Ti3+, which was caused by the charge compensation reaction derived from part of Ti4+ ions entering the V″Cu to form the donor Ti · · Cu . The impedance analysis shows that excessive CTO and TiO2 significantly reduce the grain boundary resistance of CCTO/CTO/TiO2 ceramics. Furthermore, it can be found that due to excessive CTO, TiO2 reacts with segregated CuO to form CCTO again and reduce the CuO concentration at the grain boundaries. Therefore, this significantly reduces the grain boundary width, resulting in a colossal dielectric constant of 9.0 × 105 at 30 Hz. [ABSTRACT FROM AUTHOR]

SrCu 3 Ti 4 O 12 ultrafine powders and ceramics were successfully prepared using sol-gel and ceramic techniques. DTA/TG, XRD, HRTEM, SAED, SEM, and XPS were employed to characterize the samples' thermal decomposition, phase composition, microstructure, and element valence. During calcination, the dry precursors gradually decompose into oxides and recombine into SrCu 3 Ti 4 O 12 polycrystalline above 620 °C. Simultaneously, the prepared ceramics sintered at 1025 °C for 8 h exhibited a colossal permittivity at room temperature (ε r = 8.5 × 104, 1 kHz) and good temperature stability. XPS result confirms that Cu+/Cu2+ and Ti3+/Ti4+ coexist in ceramics, and Impedance analysis indicates a low-resistance region originating from inhomogeneity in the grain interiors. Finally, the relevance between defect formation and dielectric properties in SrCu 3 Ti 4 O 12 materials is discussed. [Display omitted] • SrCu 3 Ti 4 O 12 ultrafine powders were successfully synthesized by a sol-gel method and calcinating at 925 °C. • The 1025oC-sintered SrCu 3 Ti 4 O 12 ceramics exhibit a colossal permittivity at room temperature (ε r = 8.5 × 104, 1 kHz). • Impedance analysis indicates a low-resistance region derived from the inhomogeneous semiconducting grain interiors. • The escape of copper from SCTO lattices provides an impetus to form donor defects by void-filling of high valence ions. [ABSTRACT FROM AUTHOR]

• Nano-size titanium oxides covered CCTO particles were synthesized by hydrothermal synthesis technique. • The prepared ceramics with embedding nanocrystalline structure exhibit very giant dielectric constant at room temperature. • The impedance spectra confirm there is a low resistivity region in the grain interiors of TiO 2 /CCTO composite ceramics. • A model of nanocrystalline interface barrier layer capacitor is proposed to explain the giant permittivity behaviors. [Display omitted] In this article, hydrothermal methods were employed to synthesize CaCu 3 Ti 4 O 12 -based powders with a surface coverage of nano-sized TiO 2 particles in molar ratio Ti4+/CCTO of 0, 0.1, 0.2, and 0.3. The phase structure, morphology, and compositional distribution of TiO 2 -covered CCTO powders were systematically characterized. Using the synthesized powders as starting materials, dense ceramics with very giant dielectric constants at room temperature (ε r >7.0 ×105 at 20 Hz and ε r >4.0 ×105 at 1 kHz) were successfully fabricated by sintering at 1050 °C for 8 h. Meanwhile, the embedding nanocrystalline structures were observed in grain interiors of TiO 2 -covered CCTO ceramics. The investigation of dielectric properties and impedance spectra confirm that, except the double-Schottky barriers on the grain boundaries, there is a low resistivity region in TiO 2 /CCTO composite ceramics, originated from the inhomogeneous nano-scale semiconducting regions, which formed by the dispersion of Ti4+ ions to replace Cu2+ positions in the grain interiors. According to the results, a model of nanocrystalline interface barrier layer capacitors is proposed to reasonably explain the colossal permittivity behaviors of nano-size TiO 2 -covered CCTO perovskite materials. [ABSTRACT FROM AUTHOR]

SrTiO3 dielectric ceramics were fabricated in air by using M2O3–CuO–PbO as dopants (M=Sm,Nd,La,Yb). The obtained ceramics exhibited a high dielectric constant (#x03B5;25>4880) with stable temperature characteristics. With doping the rare-earth ions from Sm → Nd → La → Yb, the corresponding dielectric constant regularly decreased. The investigation of microstructure showed that Yb additives benefited to the grain growth and CuO additives mainly segregated at the grain boundaries to form the insulation layers. According to the results, the conduction mechanism of SrTiO3–M2O3–CuO–PbO system was discussed. [Copyright &y& Elsevier]

(Y, Mn) co-doped Sr0.5Pb0.5TiO3 ceramics were fabricated by solid state reaction method. The samples’ room temperature resistivities increase and their negative temperature coefficient of resistance (NTCR)–positive temperature coefficient of resistance (PTCR) composite effects become strong with increasing Mn concentration. The investigations of scanning electron microscope and complex impedance spectra show that Mn addition confines the grain growth and increases the grain boundary resistance. In addition, electron paramagnetic resonance spectra confirm that the Mn impurities are in forms of high valence below the Curie temperature (Tc) and divalent Mn2+ cations appear above Tc. It is assumed that partial Mn cations can trap the electrons and be reduced to divalent Mn2+ cations during phase transition, which benefits to improving the PTCR effect of (Sr, Pb)TiO3-based thermistors. And the NTCR effect below Tc should be closely related to the acceptor defects in the grain boundary layers. [Copyright &y& Elsevier]

Lanthanum-doped Sr0.5Pb0.5TiO3 semiconducting ceramics were prepared by the solid state reaction technique with excess PbO additive. Samples'' resistivities rise about 5 orders of magnitude above the Curie temperature (Tc≈115 °C) and their negative temperature coefficient of resistivity (NTCR) increases with an increase of the sintering temperature. The crystalline structure, microstructure and compositional distribution were investigated using XRD, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) with X-ray energy dispersive analyses (EDAX), respectively. The distribution of Pb, Sr and Ti in the grain boundary layer has been shown to be similar to that in the grain interior. It is assumed that the PbO additive compensates Pb loss and keeps the Pb/Ti ratio stable in the grain boundary layers, which results in the low room temperature resistivity and weak NTCR effects. [Copyright &y& Elsevier]

The hydrothermal method was successfully applied in this article to prepare nano-scale SnO 2 coated CCTO composite ceramics (CCTO/xSnO 2 , X = 0, 0.1, 0.2, 0.3, 0.4). XRD, HRTEM, FESEM, EDS, XPS are systematically used to study the phase composition, surface structure, microstructure, composition distribution, and valence state of CCTO/SnO 2 composite ceramics. Sintered at a high temperature of 1040°C for 8 h, the prepared CCTO/SnO 2 composite ceramic has obtained a dense microstructure and an exceptionally colossal dielectric constant(ε r > 6.7 × 105 at 25Hz, ε r > 8.1 × 104 at 1 kHz). The impedance spectroscopy and FESEM confirmed that the CCTO/SnO 2 composite ceramics have the polarization behavior between grain boundaries on the micrometer scale and the polarization between nanocrystals on the nanometer scale. This nanoscale nanocrystalline barrier layers capacitor has become the primary source of the giant dielectric phenomenon of CCTO/SnO 2 composite ceramics. [ABSTRACT FROM AUTHOR]

In this study, Ca 1-x Sr x Cu 3 Ti 4 O 12 /TiO 2 ceramics doped with different Sr/Ca ratios and an excess of 20% nano-scale TiO 2 particles were prepared via the solid-state method (denoted as C 1-x S x CTO/TiO 2 , where x = 0, 0.2, 0.4, 0.6, 0.8, 1.0). The phase composition, microstructure, elemental distribution, elemental valence states, and electrical properties of the composite ceramics were systematically analyzed. XRD data confirmed the successful synthesis of CSCTO crystals in a series of CSCTO ceramics, and it was observed that the lattice parameters of the main phase increased as the Sr/Ca ratio in CSCTO/TiO 2 increased. Ca 0.8 Sr 0.2 Cu 3 Ti 4 O 12 /TiO 2 ceramics demonstrated a good dielectric constants (1 × 105, 1 kHz) at room temperature. Microstructure analysis revealed that the excess TiO 2 hinders the composite ceramics' crystal growth, forming pomegranate-like structures. The structure leads to a hierarchical interfacial polarization, which results in the giant dielectric response in CSCTO/TiO 2 composite ceramics. Ca 1-x Sr x Cu 3 Ti 4 O 12 /TiO 2 composite perovskite ceramics possess excellent dielectric properties, offering promising prospects for applications in electronic devices. The excess TiO 2 inhibits crystal growth, resulting in pomegranate-like nanoscale semiconductor grains, which are the source of the colossal dielectric phenomenon. [Display omitted] • Complex perovskite Ca 1-x Sr x Cu 3 Ti 4 O 12 /TiO 2 ultrafine powders were successfully synthesized by a solid-state method and calcinating at 930oC. • The 1070°C-sintered Ca 1-x Sr x Cu 3 Ti 4 O 12 /TiO 2 ceramics exhibit a colossal permittivity at room temperature (ε r = 1 × 105, 1 kHz). • XPS confirms the coexistence of Cu⁺/Cu²⁺ and Ti³⁺/Ti⁴⁺; Impedance analysis reveals the hierarchical polarization behavior at micron and nano scales in CSCTO/TiO 2. • Excessive TiO 2 inhibited the growth of CSCTO crystals, resulting in the formation of pomegranate-like nanocrystals. [ABSTRACT FROM AUTHOR]

[Display omitted] • NaF was composited into CCTO with excess Ti and successfully prepared NaF/CCTO composite ceramics. • FESEM found many nanocrystalline structures inside the grains in NaF/CCTO composite ceramics. • The dielectric constant of NaF-0.1 is 2.7 × 106 and 5.1 × 105 at 20 Hz and 1 kHz, respectively. NaF was composited into CCTO with excess Ti and successfully prepared NaF/CCTO composite ceramics (CaCu 3 Ti 4.2 O 12 -xNaF, x = 0.03, 0.05, 0.1). Meanwhile, its physical and chemical properties were systematically characterized and discussed. HRTEM can observe that some particles are deposited on the surface of CCTO. FESEM found many nanocrystalline structures inside the grains in NaF/CCTO composite ceramics. Dielectric spectroscopy confirms that the effect of NaF and excessive Ti in CCTO can significantly improve its dielectric properties. The dielectric constant of NaF-0.1 sample reaches 2.7 × 106 and 5.1 × 105 at 20 Hz and 1 kHz, respectively. [ABSTRACT FROM AUTHOR]

In this study, TiO 2 /CCTO composite ceramics with pomegranate-like grains were successfully prepared using a novel route. In addition, their microstructures, giant dielectric mechanisms, and nonlinear electrical behaviors were studied in detail. Analyses of the experimental results showed that the grains with a pomegranate-like microstructure had nano/micro-scale grain boundaries, which significantly increased the interfacial polarization at the grain and subgrain boundaries. Simultaneously, impedance analysis corroborated the existence of a low resistance region in the grain interiors. This resulted from the establishment of donor defects (T i C u..) through replacement of the Cu2+ positions with Ti4+ ions and the production of numerous weakly trapped electrons. The colossal permittivity (ε r = 4.57 × 105 at 20 Hz, ε r = 9.86 × 104 at 1 kHz) of TiO 2 /CCTO composite ceramics closely correlates to the charge accumulation on the hierarchical grain boundary barrier layers. [ABSTRACT FROM AUTHOR]

CaCu 3 Ti 4 O 12 /CaTiO 3 (CCTO/CTO) composite ceramics were prepared through in-situ reaction and solid-state sintered at 1040°C for 10 h. The phase composition, microstructure, morphology, valence, and electrical properties of ceramics are systematically studied by X-ray diffraction(XRD), Field emission scanning electron microscopy(FESEM), Electron probe micro-analysis (EPMA), X-ray photoelectron spectroscopy(XPS), and LCR instruments. It can be found that the FESEM image shows that the addition of CTO inhibits the growth of CCTO grains, and there are nanocrystals inside the grains. The EPMA mapping demonstrated which nanocrystals are composed of CCTO and a small amount of CTO. Impedance spectroscopy observed two semi-circular arcs, which correspond to the effects of micron-level grains and nano-level nanocrystals, respectively. These two mechanisms significantly affect the colossal dielectric response of CCTO/CTO composite ceramics. In this article, by comparing the fitted circuit curve in the impedance spectrum and the FESEM image, it can be found that there is a nano-level barrier effect in the CCTO-based ceramics. [Display omitted] • CCTO/CTO composite ceramics were synthesized by the solid-phase reaction method. • Part of the segregated CuO reacted with CTO. • FESEM research found that there are apparent nanocrystals inside the crystal grains. • Impedance spectroscopy observed two semi-circular arcs in the CCTO/CTO composite ceramic. [ABSTRACT FROM AUTHOR]