Search

(In0.5Nb0.5)0.005(Ti1‐xZrx)0.995O2 (INZT, x = 0‐0.10) ceramics were synthesized using a conventional sintering method, and the effects of Zr content on the microstructures, dielectric properties and electron‐pinned defect‐dipoles (EPDD) polarization of the resultant products were investigated. The solubility limit of INZT was x = 0.075, and a secondary ZrTiO4 phase appeared at x = 0.10. Ceramics with x = 0‐0.10 exhibited excellent dielectric properties, ie, colossal permittivity (CP, εʹ > 103) and low dielectric loss (tanδ < 0.1), over a wide range of frequencies (100‐106 Hz at 300 K) and temperatures (50‐350 K at 1 kHz). The dielectric spectra and XPS results confirmed that the CP property of the ceramics could be ascribed to their EPDD polarization. The activation energy (Ea) for EPDD polarization was continuously enhanced by increasing x values. EPDD relaxation parameters at different x values were revealed using Cole‐Cole equation fitting. Moreover, α, which characterize the relaxation time τ distribution, increased with x values, thus indicating that Zr was involved in and affected electron localized states. The high Ea, temperature Tp of the peak εʹʹ at 1 kHz, and dielectric relaxation time τp at 30 K were related to increases in hopping distance of electrons among defect clusters with Zr addition. [ABSTRACT FROM AUTHOR]

Low dielectric loss (tanδ < 0.05) within a frequency range of 20 Hz–2 MHz and a temperature range of 25–350 K was obtained through an optimized annealing process in colossal permittivity (CP) (εʹ > 104) (La0.5Nb0.5)0.005Ti0.995O2 ceramics. The effects of annealing on two important dielectric relaxations, electron-pinned defect-dipole (EPDD), and Maxwell–Wagner polarization were explored. An enhancement of activation energy (Ea) value and a large distribution of relaxation time τ were detected in EPDD relaxation for the ceramics annealed at 1123 K. The EPDD polarization was destroyed, accompanied by the disappearance of CP in the high annealing temperature range (> 1273 K). Impedance spectroscopy analysis suggested that grain boundary impedance could greatly enhanced as the ceramics were annealed at 1123 K. Strong electrode-material-dependent dielectric properties were detected, and a high tanδ was observed after the insulating surface layer was removed. The CP and low tanδ were ascribed to the maintenance of EPDD polarization, the enhancement of grain boundaries resistance, and the formation of an insulating surface layer through appropriate annealing. [ABSTRACT FROM AUTHOR]

The (Bi 0.5 Nb 0.5 ) x Ti 1- x O 2 (BNTO, 0 ≤ x ≤ 0.05) ceramics were synthesized by a standard conventional solid-state reaction. The effects of sintering temperature and composition x on the crystal structure, microstructure, and dielectric properties of BNTO ceramics were investigated. A pure rutile phase is achieved as x ≤ 0.01, and secondary phase Bi 1.74 Ti 2 O 6.624 is detected as x ≥ 0.025. BNTO ceramic with x = 0.025 shows a high dielectric constant (155.1 k) and low dielectric loss (0.042) at 1 kHz (room temperature). Colossal permittivity is primarily related to Maxwell-Wagner effect, electron-pinned defect-dipoles or weak-binding electron. The low dielectric loss is argued to Bi ions which are doped into TiO 2 lattice and the formation of Bi 1.74 Ti 2 O 6.624 phase. [ABSTRACT FROM AUTHOR]

Abstract A series of La+Nb co-doped TiO 2 (La 0.5 Nb 0.5) x Ti 1- x O 2 (0.25% ≤ x ≤ 5%) ceramics were prepared using a solid-state reaction method. Colossal permittivity (CP) (εʹ > 104) and low dielectric loss (tanδ < 0.05) were obtained when the ceramics were sintered at 1673 K in an N 2 atmosphere and annealed at 1073–1173 K in air. A pure rutile phase was achieved when x = 0.25% and secondary phase La 2 TiO 5 was detected when x ≥ 0.5%. The optimum dielectric performance of εʹ > 104 and tan δ < 0.05 within 1 Hz–2 MHz and 25–350 K was obtained for x = 0.5%. Three types of dielectric relaxations were observed through the dielectric-temperature spectrum: electron-pinned defect-dipoles (EPDD) polarization, electron hopping, and Maxwell–Wagner polarization. The CP (> 25 K at 1 kHz) was primarily related to EPDD polarization. The high activation energy of the grain boundary (E gb = 1.98 eV) is one of the reasons for the low tanδ in this study. Graphical abstract Image 1 Highlights • The (La 0.5 Nb 0.5) x Ti 1- x O 2 (0.25% ≤ x ≤ 5%) ceramics have been investigated. • For x = 0.5, ε r > 104 and tan δ < 0.05 within 1 Hz–2 MHz and 25–350 K. • The CP property was confirmed original from EPDD polarization. • High activation energy of the grain boundary is reason for low tanδ. [ABSTRACT FROM AUTHOR]

A series of Tl + Nb co-doped TiO 2 ceramics ((Tl 0.5 Nb 0.5 ) x % Ti 1- x % O 2 0.5 ≤  x  ≤ 10.0) were prepared by a solid-state reaction method under N 2 atmosphere. The evolution of their microstructures, and dielectric properties were systematically studied. The co-doped ceramics exhibited a tetragonal rutile structure wherein the Nb and Tl elements were homogeneously distributed. The cell volumes, grain size, and permittivity increased with doping x , whereas the impedance values of the grain and grain boundary decreased with an increasing x . The optimum dielectric performance ( ε r > 10 4 , tan δ  < 0.05) in the range of 10–10 6 Hz was obtained for x  = 1.5 with a corresponding grain boundary active energy of 0.86 eV. Four types of dielectric relaxation were observed at different temperature ranges: 10–30 K, 30–200 K, 200–350 K and 350–475 K; those dielectric relaxtions were respectively caused by electron-pinned defect-dipoles, electron hopping, oxygen vacancy hopping, and Maxwell–Wagner polarization. The colossal permittivity is primarily a result of the electron-pinned defect-dipole polarization. [ABSTRACT FROM AUTHOR]

In, Nb, and Zr co-doped TiO 2 ((In 0.5 Nb 0.5 ) 0.005 (Ti 1-x Zr x ) 0.995 O 2 ) (x = 0–0.80) ceramics were prepared by a solid-state reaction method, and their structures, dielectric properties, and response to DC bias were studied. The solubility limit was found to be near x = 0.10, and the excess added Zr was present in the form of secondary ZrTiO 4 phase. The mean grain size increased from 20.2 to 39.5 μm in the x = 0–0.10 range and then decreased to 5.2 μm for x = 0.20. Permittivity at 1 kHz exceeded 10 4 for the samples in the x = 0–0.20 range and then decreased to 570 for x = 0.40. For x = 0.20, the ceramic sample showed ε r ≈ 10 4 and tanδ ≤ 0.05 (20 Hz–100 kHz), as well as good temperature (−150 to 125 °C) and DC bias (0–875 v/cm) stability. The breakdown electric field increased from 940 v/cm for x = 0 to 5770 v/cm for x = 0.20. The excellent dielectric properties are attributed to the coexistence of smaller grains and the presence of insulating ZrTiO 4 in the sample. [ABSTRACT FROM AUTHOR]