Dielectric Properties of Colossal Permittivity Materials： An Update

During the last 10 years, a lot of interests have been devoted to the so-called CDC （colossal dielectric constant） materials. The first materials exhibiting this behavior were the perovskite-based ceramics on the CCTO （CaCuaTi4012） composition. Relative dielectric permittivity can attain values up to （or even larger than） 105. Nevertheless, their dielectric losses are too high, the lower values ranging 10%, in a narrow frequency range, thus limiting their applications. The underlying physical mechanisms at the origin of the CDC are still under study. The analysis of broadband impedance spectroscopy measurements leads most of the authors to propose an interracial polarization mechanism （at the electrodes or at internal barriers）, there is a limited number of complementary electrical characterization techniques, which, up to now, comfort the proposed interracial polarization mechanisms. In the present work, I-V and time-domain polarization are used to characterize these materials. One of the main results is the observation of a non-symmetrical response of these materials related to the direction of the polarization. These results are observed for both macroscopic level on bulk polycrystalline material and within individual grains of the same samples. These results do not fit current accepted models for polarization for CDC materials.

Colossal permittivity and ultralow dielectric loss in Nb-doped SrTiO_(3) ceramics

Defect engineering has been applied to prepare materials with modifiable dielectric properties.SrTiNbxO3(x=0,0.003,0.006,0.009,0.012)ceramics were synthesized using the traditional solid-state reaction method and sintered in a reducing atmosphere.All samples show excellent dielectric properties with giant permittivity(>3.5×10^(4))and low dielectric loss(<0.01).SrTiNb0.003O3 ceramic exhibits a colossal permittivity of 4.6×10^(4)and an ultralow dielectric loss of 0.005(1 kHz,room temperature)as well as great temperature stability in the range of(−60)–160℃.The mechanism of the presented colossal permittivity(CP)properties is investigated by conducting X-ray photoelectron spectroscopy(XPS)and analyzing activation energies.The results indicate that the introduction of Nb5+and the reducing sintering atmosphere together generated the formation of Ti^(3+)and V_(O)^(**).These defects further form Ti-V_(O)^(**)-Ti'_(Ti)defect dipoles,contributing to the coexisting giant permittivity and low dielectric loss in Nb-doped SrTiO_(3)(STN)ceramics.

Defect engineering of rutile TiO_(2) ceramics:Route to high voltage stability of colossal permittivity

Donor-acceptor co-doped rutile TiO_(2) ceramics with colossal permittivity(CP)have been extensively investigated in recent years due to their potential applications in modern microelectronics.In addition to CP and low dielectric loss,voltage stability is an essential property for CP materials utilized in high-power and high-energy density storage devices.Unfortunately,the voltage stability of CP materials based on codoped TiO_(2) does not catch enough attention.Here,we propose a strategy to enhance the voltage stability of co-doped TiO_(2),where different ionic defect clusters are formed by two acceptor ions with different radii to localize free carriers and result in high performance CP materials.The(Ta+Al+La)co-doped TiO_(2) ceramic with suitable La/Al ratio exhibits colossal permittivity with excellent temperature stability as well as outstanding dc bias stability.The density functional theory analysis suggests that La^(3+)Al^(3+)V_(0)Ti^(3+)defect clusters and Ta^(5+)-Al^(3+)pairs are responsible for the excellent dielectric properties in(Ta+Al+La)co-doped TiO_(2).The results and mechanisms presented in this work open up a feasible route to design high performance CP materials via defect engineering.

Hole-pinned defect-dipoles induced colossal permittivity in Bi doped SrTiO3 ceramics with Sr deficiency

Bi doped SrTiO3 ceramics with Sr deficiency,i.e.Sr1-1.5xBixTiO3(x=0,0.01,0.05,0.1),were prepared via conventional solid-state reaction route.A colossal permittivity(CP)over 104 with low dielectric loss less than 0.05wasobtained in x=0.05 Sr1-1.5xBixTiO3 ceramics.In addition,the dielectric constant is maintained at a value greater than 104 in the range of 102-105 Hz and almost frequency independent.Phase structure analysis and density functional theory calculations suggest that the Bi·Sr-V"Sr-Bi·Sr defect complex with hole-pinned defect-dipoles maybe responsible for the high-performance CP properties.This work gives a new way to achieve high performance CP materials in ABO3 perovskite ceramics.

Thermal stable and ultralow dielectric loss in(Gd_(0.5)Ta_(0.5))_(x)Ti_(1-x)O_(2)giant permittivity ceramics by defect engineering

High dielectric loss and poor temperature stability are the current barriers to the application of dielectric materials.In present work,we synthesized a system of acceptor Gd^(3+)and donor Ta^(5+)co-doped(Gd_(0.5)Ta_(0.5))_(x)Ti_(1-x)O_(2)(GTTOx,x=0,0.01,0.02,0.04,0.06)ceramics to enhance dielectric response.It was found that a colossal permittivity(CP,2.65×10^(4)@1 kHz,2.37×10^(4)@1 MHz),a very low dielectric loss(tanδ,0.007@1 kHz,0.03@1 MHz),good stability of frequency(20–10^(6)Hz)and temperature(RT–250°C,Δε′(T)/ε′30<±15%,at 1 kHz)were achieved simultaneously in GTTO0.01 ceramic.Complex impedance spectroscopy,XPS,SEM,and Raman spectroscopy were used to investigate the reasons for the improved dielectric properties.The result indicated that the main reasons for CP and low dielectric loss are the synergistic effect of the electron pinning defect-dipole(EPDD)model,the internal blocking layer capacitance(IBLC)mechanism,and electrode response.This work provides a promising approach for the design of defect-related high-performance giant dielectric ceramics.

Ultraelow loss tangent and giant dielectric permittivity with excellent temperature stability of TiO_(2) co-doped with isovalent-Zr4þ/ pentavalent-Ta5þ ions

The excellent giant dielectric properties(ExGDPs)are represented in the isovalenteZr4þ/pentavalent eTa5þions coedoped TiO_(2) with different coedoping percentages(x%ZrTTO).The dopants were dispersed homogeneously in a highly compactegrained ZrTTO microstructure.The mean grain size and cell parameters with bond lengths slightly enlarged as x%increased.The(1%e5%)ZrTTO oxides exhibited ultra elow tand values of 0.004e0.016 with the giant dielectric permittivity(ε0~2.7e3.7104);while theε0 of the 5%ZrTTO was slightly dependent on the temperature ranging from--60 to 200C,following the temperature dependence requirement for application in the X7/8/9R capacitors.Impedance spectroscopy showed a very large resistance of the grain boundaries.The dielectric properties of the 1%ZrTTO were strongly dependent on the applied DC electric field,indicating the dominant internal barrier layer capacitor(IBLC)effect.However,the dielectric properties of the 5%ZrTTO were nearly independent on the applied DC electric field up to 30 V/mm,which was primarily resulted from electron localization in defect dipoles.Therefore,the ExGDPs of the x%ZrTTO were attributed to the combined effects of the IBLC and localizedeelectron defectedipoles related to oxygen vacancies(Ti4þ,e--VO--e--,Ti4þand 3Ti4þ,e----VO--TaTi)and Ti4þ,e--TaTi.

Novel titanium dioxide ceramics containing bismuth and antimony

Here,we developed one kind of novel TiO_(2) ceramics with colossal dielectric constant by chemical modifications(Bi^(3+) and Sb^(5+)),and discussed the physical origin for giant dielectric constant.Effects of Bi and/or Sb on their microstructure,dielectric properties as well as its frequency and temperature stability were studied in detail.It was found that their dielectric properties are strongly sensitive to(Bi,Sb)contents,and colossal dielectric permittivity(CP)(10^(4)~10^(5))together with low dielectric loss(~5.7%)can be obtained in a wide composition range.In addition,all the ceramics possessed good frequency(10^(2)~10^(6)Hz)and temperature(-150-200℃)stability of dielectric properties.In addition,the defects caused by the Bi volatilization may be the reason for higher dielectric properties of(Bi_(0.5)Sb_(0.5))_(x)Ti_(1-x)O_(2) ceramics with respect to(A_(0.5)Sb_(0.5))_(x)Ti_(1-x)O_(2)(A=In,Pr,Dy,Sm,Gd,Yb,Ga,Al,Fe or Sc).According to the results of complex impedance and XPS,the electron-pinned defect-dipoles may be suitable to explain the CP phenomenon,and oxygen vacancies-induced by Bi^(3+)&Sb^(5+) substitution for Ti^(4+) should be responsible for conduction mechanism.We believe that this profound investigation can benefit the development of TiO_(2) ceramics as a CP material.