In this study,(Zr_(0.5)/Sb_(0.5))xTi_(1−x)O_(2) ceramics with x=0.01,0.025,and 0.05 were prepared via the solid-state reaction(SSR)method.A pure phase of rutile TiO_(2) with a highly dense microstructure and relative ...In this study,(Zr_(0.5)/Sb_(0.5))xTi_(1−x)O_(2) ceramics with x=0.01,0.025,and 0.05 were prepared via the solid-state reaction(SSR)method.A pure phase of rutile TiO_(2) with a highly dense microstructure and relative density(ρr)higher than 96%was detected in all the sintered ceramics.The mean grain size was reduced,but the dielectric permittivity(ε′)increased.The giant dielectric properties were tested to investigate their possible use in capacitors and capacitive humidity sensors under various relative humidity(RH)levels ranging from 30%to 95%RH.(Zr_(0.5)/Sb_(0.5))xTi_(1−x)O_(2) ceramics present a giantε′of~(4.82‒7.39)×10^(4) and a low loss tangent(tanδ≈0.031‒0.106 at 1 kHz),indicating attractive giant dielectric properties.This observation was attributed to both intrinsic and extrinsic effects.For the humidity sensing properties,the best humidity sensing properties were observed in the ceramics with x=0.05,with a sensitivity of~237%pF/%RH,a low hysteresis error(~1.6%),and fast response/recovery time of~12 s/16 s at 1 kHz.The point defects of Sb⋅Ti and V_(O)^(··) were claimed to be active centers for water absorption.Furthermore,impedance spectroscopy(IS)analysis revealed that changes in the dielectric properties with varying RH levels were also influenced by interfacial polarization at the surface layer and grain boundaries.展开更多
Colossal permittivity(CP)materials,particularly co-doped TiO_(2) ceramics,have garnered significant attention for their potential in high-performance ceramic capacitors.However,understanding the origin of CP remains a...Colossal permittivity(CP)materials,particularly co-doped TiO_(2) ceramics,have garnered significant attention for their potential in high-performance ceramic capacitors.However,understanding the origin of CP remains a challenge,with the role of doping ratios between acceptor and donor ions largely underexplored.This study addresses this gap by systematically investigating the effects of Ga^(3+)concentrations on the microstructure and CP of Ga_(y)Nb_(0.025)Ti_(0.975-y)O_(2),prepared via the solid-state reaction method.The sintered ceramics exhibited a dense rutile TiO_(2) phase with increasing grain sizes and oxygen vacancies.Notably,CP values as high as 10^(5) were achieved at Ga^(3+)/Nb^(5+)ratio<1.0.Optimal dielectric properties were observed at Ga^(3+)/Nb^(5+)=1.0,yielding a CP of 6.4×10^(4) and a loss tangent<0.03,surpassing the performance of many existing CP materials.Impedance spectroscopy revealed distinct electrical heterogeneity,with conductive grains and highly resistive grain boundaries with activation energies>1.0 eV.Ceramics with 5%Ga^(3+) doping showed diminished CP due to the absence of semiconducting grains.The findings suggest that CP originates from the internal barrier layer capacitor.This study not only elucidates the crucial role of doping ratios in tailoring CP but also establishes a pathway for developing advanced dielectric materials with superior performance for ceramic capacitors.展开更多
The giant dielectric bchavior of CaCu_(3)Ti_(4)0_(12)(CCTO)has been widely investigated owing to its potential applications in electronics;however,the loss tangent(tan8)of this material is too large for many applicati...The giant dielectric bchavior of CaCu_(3)Ti_(4)0_(12)(CCTO)has been widely investigated owing to its potential applications in electronics;however,the loss tangent(tan8)of this material is too large for many applications.A partial substitution of CCTO ceramics with either Al^(3+) or Ta^(5+)-ions generally results in poorer nonlinear properties and an associated increase in tan8(to~0.29-1.15).However,first-principles calculations showed that self-charge compensation occurs between these two dopant ions when co-doped into Tit sites,which can improve the electrical properties of the grain boundary(GB).Surprisingly,in this study,a greatly enhanced breakdown electric field(~200--6588 V/cm)and nonlinear coefficient(-4.8-15.2)with a significantly reduced tan8(~0.010--0.036)were obtained by simultaneous partial substitution of CCTO with acceptor-donor(Al^(3+),Ta^(5+))dopants to produce(Al^(3+),Ta^(5+))-CCTO ceramics.The reduced tan8 and improved nonlinear properties were attributed to the synergistic effects of the co-dopants in the doped CCTO structure.The signifcant reduction in the mean grain size of the(Al^(3+),Ta^(5+))-CCTO ceramics compared to pure CCTO was mainly because of the Ta^(5+)-ions.Accordingly,the increased GB density due to the reduced grain size and the larger Schottky barrier height(Ф_(b))at the GBs of the co-doped CCTO ceramics were the main reasons for the greatly increased GB resistance,improved nonlinear properties,and reduced tan8 values compared to pure and single-doped CCTO.In addition,high dielectric constant values(ε'≈(0.52-2.7)×10^(4))were obtained.A fine-grained microstructure with highly insulating GBs was obtained by Ta doping,while co-doping with Ta^(5+) and Al^(3+ )resulted in a high Ф_(b).The obtained results are expected to provide useful guidelines for developing new giant dielectric ceramics with excellent dielectric properties.展开更多
In this work,the surface modification using a two-steps plasma etching has been developed for enhancing energy conversion performance in polytetrafluoroethylene(PTFE)triboelectric nanogenerator(TENG).Enhancing surface...In this work,the surface modification using a two-steps plasma etching has been developed for enhancing energy conversion performance in polytetrafluoroethylene(PTFE)triboelectric nanogenerator(TENG).Enhancing surface area by a powerful O_(2) and Ar bipolar pulse plasma etching without the use of CF_(4) gas has been demonstrated for the first time.TENG with modified surface PTFE using a sequential two-step O_(2)/Ar plasma has a superior power density of 9.9 W·m^(-2),which is almost thirty times higher than that of a pristine PTFE TENG.The synergistic combination of high surface area and charge trapping sites due to chemical bond defects achieved from the use of a sequential O_(2)/Ar plasma gives rise to the intensified triboelectric charge density and the enhancement of power output of PTFE-based TENG.The effects of plasma species and plasma etching sequence on surface morphologies and surface chemical species were investigated by a field emission scanning electron microscopy(FESEM),atomic force microscopy(AFM),and X-ray photoelectron spectroscopy(XPS).The correlation of surface morphology,chemical structure,and TENG performance was elucidated.In addition,the applications of mechanical energy harvesting for lighting,charging capacitors,keyboard sensing and operating a portable calculator were demonstrated.展开更多
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 homogene...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.展开更多
基金funded by the National Research Council of Thailand(NRCT)(No.N41A640084)This project was also funded by the National Science,Research,and Innovation Fund(NSRF)and the Fundamental Fund,and Graduate Studies Office of Khon Kaen UniversityThis work has received a scholarship under the Post Doctoral Training for Frontier Research from Khon Kaen University,Thailand(No.PD2567-07).
文摘In this study,(Zr_(0.5)/Sb_(0.5))xTi_(1−x)O_(2) ceramics with x=0.01,0.025,and 0.05 were prepared via the solid-state reaction(SSR)method.A pure phase of rutile TiO_(2) with a highly dense microstructure and relative density(ρr)higher than 96%was detected in all the sintered ceramics.The mean grain size was reduced,but the dielectric permittivity(ε′)increased.The giant dielectric properties were tested to investigate their possible use in capacitors and capacitive humidity sensors under various relative humidity(RH)levels ranging from 30%to 95%RH.(Zr_(0.5)/Sb_(0.5))xTi_(1−x)O_(2) ceramics present a giantε′of~(4.82‒7.39)×10^(4) and a low loss tangent(tanδ≈0.031‒0.106 at 1 kHz),indicating attractive giant dielectric properties.This observation was attributed to both intrinsic and extrinsic effects.For the humidity sensing properties,the best humidity sensing properties were observed in the ceramics with x=0.05,with a sensitivity of~237%pF/%RH,a low hysteresis error(~1.6%),and fast response/recovery time of~12 s/16 s at 1 kHz.The point defects of Sb⋅Ti and V_(O)^(··) were claimed to be active centers for water absorption.Furthermore,impedance spectroscopy(IS)analysis revealed that changes in the dielectric properties with varying RH levels were also influenced by interfacial polarization at the surface layer and grain boundaries.
基金funded by the National Science,Research,and Innovation Fund(NSRF)and the Fundamental Fund of Khon Kaen Universitypartially supported by the Research of Khon Kaen Universitythe Thailand Graduate Institute of Science and Technology(TGIST)for his Ph.D.scholarship[Grant Number SCA-CO-2558-1033-TH].
文摘Colossal permittivity(CP)materials,particularly co-doped TiO_(2) ceramics,have garnered significant attention for their potential in high-performance ceramic capacitors.However,understanding the origin of CP remains a challenge,with the role of doping ratios between acceptor and donor ions largely underexplored.This study addresses this gap by systematically investigating the effects of Ga^(3+)concentrations on the microstructure and CP of Ga_(y)Nb_(0.025)Ti_(0.975-y)O_(2),prepared via the solid-state reaction method.The sintered ceramics exhibited a dense rutile TiO_(2) phase with increasing grain sizes and oxygen vacancies.Notably,CP values as high as 10^(5) were achieved at Ga^(3+)/Nb^(5+)ratio<1.0.Optimal dielectric properties were observed at Ga^(3+)/Nb^(5+)=1.0,yielding a CP of 6.4×10^(4) and a loss tangent<0.03,surpassing the performance of many existing CP materials.Impedance spectroscopy revealed distinct electrical heterogeneity,with conductive grains and highly resistive grain boundaries with activation energies>1.0 eV.Ceramics with 5%Ga^(3+) doping showed diminished CP due to the absence of semiconducting grains.The findings suggest that CP originates from the internal barrier layer capacitor.This study not only elucidates the crucial role of doping ratios in tailoring CP but also establishes a pathway for developing advanced dielectric materials with superior performance for ceramic capacitors.
基金supported by the Basic Research Fund of Khon Kaen University.It was partially supported by the Research Network NANOTEC(RNN)program of the National Nanotechnology Center(NANOTEC),NSTDA,Ministry of Higher Education,Science,Research,and Innovation(MHESI,Thailand)(Grant No.PI851882)Khon Kaen University,Thailand.J.Boonlakhom would like to thank the Graduate School of Khon Kaen University(Grant No.581T211)for his Ph.D.scholarship.
文摘The giant dielectric bchavior of CaCu_(3)Ti_(4)0_(12)(CCTO)has been widely investigated owing to its potential applications in electronics;however,the loss tangent(tan8)of this material is too large for many applications.A partial substitution of CCTO ceramics with either Al^(3+) or Ta^(5+)-ions generally results in poorer nonlinear properties and an associated increase in tan8(to~0.29-1.15).However,first-principles calculations showed that self-charge compensation occurs between these two dopant ions when co-doped into Tit sites,which can improve the electrical properties of the grain boundary(GB).Surprisingly,in this study,a greatly enhanced breakdown electric field(~200--6588 V/cm)and nonlinear coefficient(-4.8-15.2)with a significantly reduced tan8(~0.010--0.036)were obtained by simultaneous partial substitution of CCTO with acceptor-donor(Al^(3+),Ta^(5+))dopants to produce(Al^(3+),Ta^(5+))-CCTO ceramics.The reduced tan8 and improved nonlinear properties were attributed to the synergistic effects of the co-dopants in the doped CCTO structure.The signifcant reduction in the mean grain size of the(Al^(3+),Ta^(5+))-CCTO ceramics compared to pure CCTO was mainly because of the Ta^(5+)-ions.Accordingly,the increased GB density due to the reduced grain size and the larger Schottky barrier height(Ф_(b))at the GBs of the co-doped CCTO ceramics were the main reasons for the greatly increased GB resistance,improved nonlinear properties,and reduced tan8 values compared to pure and single-doped CCTO.In addition,high dielectric constant values(ε'≈(0.52-2.7)×10^(4))were obtained.A fine-grained microstructure with highly insulating GBs was obtained by Ta doping,while co-doping with Ta^(5+) and Al^(3+ )resulted in a high Ф_(b).The obtained results are expected to provide useful guidelines for developing new giant dielectric ceramics with excellent dielectric properties.
基金supported by the RNN program of the NANOTEC,NSTDA,Ministry of Higher Education,Science,Research and Innovation(MHESI)and Khon Kaen University,Thailand,the Thailand Research Fund(No.MRG6280196)the Thailand Center of Excellence in Physics(ThEP),and the Basic Research Fund of Khon Kaen University.
文摘In this work,the surface modification using a two-steps plasma etching has been developed for enhancing energy conversion performance in polytetrafluoroethylene(PTFE)triboelectric nanogenerator(TENG).Enhancing surface area by a powerful O_(2) and Ar bipolar pulse plasma etching without the use of CF_(4) gas has been demonstrated for the first time.TENG with modified surface PTFE using a sequential two-step O_(2)/Ar plasma has a superior power density of 9.9 W·m^(-2),which is almost thirty times higher than that of a pristine PTFE TENG.The synergistic combination of high surface area and charge trapping sites due to chemical bond defects achieved from the use of a sequential O_(2)/Ar plasma gives rise to the intensified triboelectric charge density and the enhancement of power output of PTFE-based TENG.The effects of plasma species and plasma etching sequence on surface morphologies and surface chemical species were investigated by a field emission scanning electron microscopy(FESEM),atomic force microscopy(AFM),and X-ray photoelectron spectroscopy(XPS).The correlation of surface morphology,chemical structure,and TENG performance was elucidated.In addition,the applications of mechanical energy harvesting for lighting,charging capacitors,keyboard sensing and operating a portable calculator were demonstrated.
基金funded by the National Research Council of Thailand(NRCT)(N41A640084 and N41A640193).
文摘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.
