To get a dielectric material with a high dielectric permittivity and suppressed dielectric loss,nano-Ag with a particle size of 20 nm and Ag@TiO_(2)core-shell particles with diameters of approximately 70-120 nm were e...To get a dielectric material with a high dielectric permittivity and suppressed dielectric loss,nano-Ag with a particle size of 20 nm and Ag@TiO_(2)core-shell particles with diameters of approximately 70-120 nm were embedded in polyvinylidene fluoride(PVDF)to fabricate nano-Ag/Ag@TiO_(2)/PVDF composites.After being modified by nano-Ag with 3 vol%optimal amount,the relative permittivity(ε_r)at 100 Hz of 50 vol%Ag@TiO_(2)/PVDF composites was 61,and the dielectric loss can be suppressed to 0.04,almost 96.4%lower than that of unmodified composites,and a higher frequency stability of bothε_r and loss has also been found.The underlying mechanism of the reduced loss was attributed to Maxwell-Wagner polarization and the Coulomb blockade effect caused by the introduction of a small amount of nano-Ag,which will block the movement of electrons between metal nanoparticles and composites.The space charge polarization and conductance loss are weakened at lower and higher Ag@TiO_(2)filling ratios,respectively,thus leading to a very low loss of the composites.展开更多
Detailed structural and dielectric properties of Lanthanum-doped barium titanate Ba_(1-x)La_(x)Tie_(1-x/4)O_(3)ceramic powders BLTx(where x=0:00;0.10;0.20;0.30 and 0.40)/BT,BLT10,BLT20,BLT30 and BLT40,synthesized by t...Detailed structural and dielectric properties of Lanthanum-doped barium titanate Ba_(1-x)La_(x)Tie_(1-x/4)O_(3)ceramic powders BLTx(where x=0:00;0.10;0.20;0.30 and 0.40)/BT,BLT10,BLT20,BLT30 and BLT40,synthesized by the sol gel process,calcined at 900℃for 3 h and sintered at 1250○C for 6 h,have been investigated.The phase formation and crystal structure of the samples were checked by X-ray diffraction(XRD)and Raman spectroscopy.The samples crystallize in the pure perovskite structure that transforms from tetragonal to pseudocubic under doping with La;results that have been confirmed by Rietveld Refinement technique.The estimated average crystallite size of the samples was about 23 nm.Dielectric parameters(dielectric permittivity and losses)were determined in the temperature range room temperature(RT)-280℃and in the frequency range 500 Hz-2 MHz.La doping gives rise to a strong decrease of the ferro-to-paraelectric transition temperature,and the frequency dependence of the permittivity shows that the samples with x=0.00 and x=0.10 reach their resonance frequency.The frequency dependence of impedance and electric modulus properties were studied over a wide frequency range from 1 kHz to 2MHz at various temperatures to confirm the contributions from grains and grain-boundaries.The complex impedance analysis data have been presented in the Nyquist plot which is used to identify the corresponding equivalent circuit and fundamental circuit parameters;it was found that the grain boundaries resistance is dominant at room temperature.The frequency dependence of the parameters permittivity,losses and AC conductivity reveals that the relaxation process is of the Maxwell-Wagner type of interfacial polarization.展开更多
In this study, dielectric properties within 8-12 GHz microwave frequencies, inductively coupled plasma-atomic emis- sion spectrometry, Fourier transform infrared spectrometry, synchronized two thermal analyses, and 57...In this study, dielectric properties within 8-12 GHz microwave frequencies, inductively coupled plasma-atomic emis- sion spectrometry, Fourier transform infrared spectrometry, synchronized two thermal analyses, and 57Fe Mossbauer spectroscopy analysis of chalcedony, agate, and zultanite samples from Turkey are presented. Agate and chalcedony show the same nine vibrational absorption peaks obtained unlike zultanite from FTIR spectra in the 350 cm-1 to 4000 cm-1 range, ε' values of chalcedony, agate and zultanite derived at 10.5 GHz were 4.67, 4.41, and 7.34, respectively, eI and e~ values of the studied samples at the microwave frequencies are related to the percentage weight of their constituent parts in their chemical compositions. 57Fe Mossbauer spectroscopy results confirm the existence of iron-containing islands in the crystal structure of zultanite, agate, and chalcedony samples, equipped them with magnetic features typical for magnetic nanoparticles including superparamagnetism. The presence of iron-containing islands significantly affects the magnetic, dielectric, and optical properties of studied samples that are not observed for pure minerals without any foreign inclusions.展开更多
An eighth-order Landau–Devonshire theory is constructed to investigate the piezoelectric and electro–optic properties of tetragonal(1- x)Pb(Mg1/3Nb2/3)O3–xPbTiO3 single crystals(x = 0.38 and x = 0.4). The die...An eighth-order Landau–Devonshire theory is constructed to investigate the piezoelectric and electro–optic properties of tetragonal(1- x)Pb(Mg1/3Nb2/3)O3–xPbTiO3 single crystals(x = 0.38 and x = 0.4). The dielectric stiffness coefficients of the Landau potential are obtained by fitting to the dielectric properties and the phase transition temperature between cubic phase and tetragonal phase. It is indicated that tetragonal(1- x)Pb(Mg1/3Nb2/3)O3–xPbTiO3 single crystals have the firstorder cubic-tetragonal phase transitions. The dielectric constants are in great agreement with the experimental results.The piezoelectric coefficients d33 and d31at room temperature are about 145 p C/N and-62 p C/N respectively which are smaller than that of(1- x)Pb(Mg1/3Nb2/3)O3–xPbTiO3 single crystals around the morphotropic phase boundary.Moreover, tetragonal(1- x)Pb(Mg1/3Nb2/3)O3–xPbTiO3 single crystals have the linear electro–optic coefficients rc =33.7 pm/V and rc = 28.8 pm/V for x = 0.38 and x = 0.4, respectively which are in accordance with the measurements.展开更多
In this paper, we performed calculations to investigate the dielectric, piezoelectric properties, Born effective charge (BEC), and spontaneous polarization of Sr2M207, the method used in our study was a well-known d...In this paper, we performed calculations to investigate the dielectric, piezoelectric properties, Born effective charge (BEC), and spontaneous polarization of Sr2M207, the method used in our study was a well-known density functional theory based on first-principles. The optimized results were in good agreement with previous experiments and calculations. which indicates that our calculated method is reasonable. The research we have done suggested that greater piezoelectric components of Sr2Nb207 were e31 and e33, and the contributions were derived from the A I. By studying the Born effective charge, it could be seen that the valence of ions changed, and the O of Sr2Nb207 were most obviously that caused by the covalent character of ions and the hybridization of O-2p and Nb-4d. The spontaneous polarization of Sr2Nb2O7 in the [001 ] direction is 25 p_C/cm2, while for Sr2Ta2O7, there was no spontaneous polarization in the paraelectric state. Finally, the effect of pressure on the piezoelectric properties were also investigated, the polarization of Sr2Nb2O7 decreased linearly with the increase alter pressure. All our preliminary results throw light on the nature of dielectric, piezoelectric properties, Born effective charge, and spontaneous polarization of Sr2M2OT, it was helpful for experimental research, the development of new materials, and future applications.展开更多
With the advantages of its fast speed,effective and moderate controllable conditions,desulfurization of coal by microwave has become research focus in the field of clean coal technology.Coal is a homogeneous mixture w...With the advantages of its fast speed,effective and moderate controllable conditions,desulfurization of coal by microwave has become research focus in the field of clean coal technology.Coal is a homogeneous mixture which consists of various components with different dielectric properties,so their abilities to absorb microwaves are different,and the sulfur-containing components are better absorbers of microwave,which makes them can be selectively heated and reacted under microwave irradiation.There still remain controversies on the principle of microwave desulfurization at present,thermal effects or non-thermal effects.The point of thermal effects of microwave is mainly base on its characters of rapidly and selectly heating.While,in view of non-thermal effect,direct interactions between the microwave electromagnetic field and sulfur containing components are proposed.It is a fundamental problem to determine the dielectric properties of coal and the sulfur-containing components to reveal the interaction of microwave and sulfur-containing compounds.However,the test of dielectric property of coal is affected by many factors,which makes it difficult to measure dielectric properties accurately.In order to achieve better desulfurization effect,the researchers employ methods of adding chemical additives such as acid,alkali,oxidant,reductant,or changing the reaction atmosphere,or combining with other methods such as magnetic separation,ultrasonic and microorganism.Researchers in this field have also put forward several processes,and have obtained a number of patents.Obscurity of microwave desulfurization mechanism,uncertainties in qualitative and quantitative analysis of sulfur-containing functional groups in coal,and the lack of special microwave equipment have limited further development of microwave desulfurization technology.展开更多
基金Funded by the National Natural Science Foundation of China(No.51772107)the Fundamental Research Funds for the Central Universities(No.2017KFYXJJ022)。
文摘To get a dielectric material with a high dielectric permittivity and suppressed dielectric loss,nano-Ag with a particle size of 20 nm and Ag@TiO_(2)core-shell particles with diameters of approximately 70-120 nm were embedded in polyvinylidene fluoride(PVDF)to fabricate nano-Ag/Ag@TiO_(2)/PVDF composites.After being modified by nano-Ag with 3 vol%optimal amount,the relative permittivity(ε_r)at 100 Hz of 50 vol%Ag@TiO_(2)/PVDF composites was 61,and the dielectric loss can be suppressed to 0.04,almost 96.4%lower than that of unmodified composites,and a higher frequency stability of bothε_r and loss has also been found.The underlying mechanism of the reduced loss was attributed to Maxwell-Wagner polarization and the Coulomb blockade effect caused by the introduction of a small amount of nano-Ag,which will block the movement of electrons between metal nanoparticles and composites.The space charge polarization and conductance loss are weakened at lower and higher Ag@TiO_(2)filling ratios,respectively,thus leading to a very low loss of the composites.
文摘Detailed structural and dielectric properties of Lanthanum-doped barium titanate Ba_(1-x)La_(x)Tie_(1-x/4)O_(3)ceramic powders BLTx(where x=0:00;0.10;0.20;0.30 and 0.40)/BT,BLT10,BLT20,BLT30 and BLT40,synthesized by the sol gel process,calcined at 900℃for 3 h and sintered at 1250○C for 6 h,have been investigated.The phase formation and crystal structure of the samples were checked by X-ray diffraction(XRD)and Raman spectroscopy.The samples crystallize in the pure perovskite structure that transforms from tetragonal to pseudocubic under doping with La;results that have been confirmed by Rietveld Refinement technique.The estimated average crystallite size of the samples was about 23 nm.Dielectric parameters(dielectric permittivity and losses)were determined in the temperature range room temperature(RT)-280℃and in the frequency range 500 Hz-2 MHz.La doping gives rise to a strong decrease of the ferro-to-paraelectric transition temperature,and the frequency dependence of the permittivity shows that the samples with x=0.00 and x=0.10 reach their resonance frequency.The frequency dependence of impedance and electric modulus properties were studied over a wide frequency range from 1 kHz to 2MHz at various temperatures to confirm the contributions from grains and grain-boundaries.The complex impedance analysis data have been presented in the Nyquist plot which is used to identify the corresponding equivalent circuit and fundamental circuit parameters;it was found that the grain boundaries resistance is dominant at room temperature.The frequency dependence of the parameters permittivity,losses and AC conductivity reveals that the relaxation process is of the Maxwell-Wagner type of interfacial polarization.
基金supported by the Project LO1305 and Operational Program Education for Competitiveness-European Social Fund of the Ministry of Education,Youth and Sports of the Czech Republic(Grant No.CZ.1.07/2.3.00/20.0155)the Internal Student Grant IGA of Palacky University in Olomouc,Czech Republic(Grant No.IGA PrF 2014017)
文摘In this study, dielectric properties within 8-12 GHz microwave frequencies, inductively coupled plasma-atomic emis- sion spectrometry, Fourier transform infrared spectrometry, synchronized two thermal analyses, and 57Fe Mossbauer spectroscopy analysis of chalcedony, agate, and zultanite samples from Turkey are presented. Agate and chalcedony show the same nine vibrational absorption peaks obtained unlike zultanite from FTIR spectra in the 350 cm-1 to 4000 cm-1 range, ε' values of chalcedony, agate and zultanite derived at 10.5 GHz were 4.67, 4.41, and 7.34, respectively, eI and e~ values of the studied samples at the microwave frequencies are related to the percentage weight of their constituent parts in their chemical compositions. 57Fe Mossbauer spectroscopy results confirm the existence of iron-containing islands in the crystal structure of zultanite, agate, and chalcedony samples, equipped them with magnetic features typical for magnetic nanoparticles including superparamagnetism. The presence of iron-containing islands significantly affects the magnetic, dielectric, and optical properties of studied samples that are not observed for pure minerals without any foreign inclusions.
基金Project supported by the National Natural Science Foundation of China(Grant No.51335002)the Changzhou Science and Technology Project,China(Grant No.CJ20130022)the Priority Academic Program Development of Jiangsu Higher Education Institutions,China
文摘An eighth-order Landau–Devonshire theory is constructed to investigate the piezoelectric and electro–optic properties of tetragonal(1- x)Pb(Mg1/3Nb2/3)O3–xPbTiO3 single crystals(x = 0.38 and x = 0.4). The dielectric stiffness coefficients of the Landau potential are obtained by fitting to the dielectric properties and the phase transition temperature between cubic phase and tetragonal phase. It is indicated that tetragonal(1- x)Pb(Mg1/3Nb2/3)O3–xPbTiO3 single crystals have the firstorder cubic-tetragonal phase transitions. The dielectric constants are in great agreement with the experimental results.The piezoelectric coefficients d33 and d31at room temperature are about 145 p C/N and-62 p C/N respectively which are smaller than that of(1- x)Pb(Mg1/3Nb2/3)O3–xPbTiO3 single crystals around the morphotropic phase boundary.Moreover, tetragonal(1- x)Pb(Mg1/3Nb2/3)O3–xPbTiO3 single crystals have the linear electro–optic coefficients rc =33.7 pm/V and rc = 28.8 pm/V for x = 0.38 and x = 0.4, respectively which are in accordance with the measurements.
基金Project supported by the National Natural Science Foundation of China(Grant No.51672220)the 111 Program of the Ministry of Education of China(Grant No.B08040)+3 种基金the National Defense Science Foundation(Grant No.32102060303)the Xi’an Science and Technology Foundationthe Shaanxi Provincial Science Foundationthe Gaofeng Project of Northwestern Polytechnical University,China(Grant No.17GH020824)
文摘In this paper, we performed calculations to investigate the dielectric, piezoelectric properties, Born effective charge (BEC), and spontaneous polarization of Sr2M207, the method used in our study was a well-known density functional theory based on first-principles. The optimized results were in good agreement with previous experiments and calculations. which indicates that our calculated method is reasonable. The research we have done suggested that greater piezoelectric components of Sr2Nb207 were e31 and e33, and the contributions were derived from the A I. By studying the Born effective charge, it could be seen that the valence of ions changed, and the O of Sr2Nb207 were most obviously that caused by the covalent character of ions and the hybridization of O-2p and Nb-4d. The spontaneous polarization of Sr2Nb2O7 in the [001 ] direction is 25 p_C/cm2, while for Sr2Ta2O7, there was no spontaneous polarization in the paraelectric state. Finally, the effect of pressure on the piezoelectric properties were also investigated, the polarization of Sr2Nb2O7 decreased linearly with the increase alter pressure. All our preliminary results throw light on the nature of dielectric, piezoelectric properties, Born effective charge, and spontaneous polarization of Sr2M2OT, it was helpful for experimental research, the development of new materials, and future applications.
文摘With the advantages of its fast speed,effective and moderate controllable conditions,desulfurization of coal by microwave has become research focus in the field of clean coal technology.Coal is a homogeneous mixture which consists of various components with different dielectric properties,so their abilities to absorb microwaves are different,and the sulfur-containing components are better absorbers of microwave,which makes them can be selectively heated and reacted under microwave irradiation.There still remain controversies on the principle of microwave desulfurization at present,thermal effects or non-thermal effects.The point of thermal effects of microwave is mainly base on its characters of rapidly and selectly heating.While,in view of non-thermal effect,direct interactions between the microwave electromagnetic field and sulfur containing components are proposed.It is a fundamental problem to determine the dielectric properties of coal and the sulfur-containing components to reveal the interaction of microwave and sulfur-containing compounds.However,the test of dielectric property of coal is affected by many factors,which makes it difficult to measure dielectric properties accurately.In order to achieve better desulfurization effect,the researchers employ methods of adding chemical additives such as acid,alkali,oxidant,reductant,or changing the reaction atmosphere,or combining with other methods such as magnetic separation,ultrasonic and microorganism.Researchers in this field have also put forward several processes,and have obtained a number of patents.Obscurity of microwave desulfurization mechanism,uncertainties in qualitative and quantitative analysis of sulfur-containing functional groups in coal,and the lack of special microwave equipment have limited further development of microwave desulfurization technology.