0.5BiDyxFe1-xO3-0.5PbTiOa（0.5BDxF1-x-0.5PT） （x=0.00, 0.05, 0.10, 0.15, 0.20） multiferroic composites were pre- pared by conventional solid state reaction method. Structural characterization was performed by X-ray ...0.5BiDyxFe1-xO3-0.5PbTiOa（0.5BDxF1-x-0.5PT） （x=0.00, 0.05, 0.10, 0.15, 0.20） multiferroic composites were pre- pared by conventional solid state reaction method. Structural characterization was performed by X-ray diffraction and the mate- rials showed tetragonal structure at room temperature. Surface morphology of the composites was studied by a scanning electron microscope （SEM）. Frequency and temperature dependence of dielectric constant （er） and dielectric loss （tan~） of 0.5BDxF1_x- 0.5PT were measured in a wide range of frequency （100 Hz to 1 MHz） and temperature （25 to 400 ~C）. The analysis of the study showed that the er and tang decreased with increasing frequency in the given range for all the samples which could be explained through the occurrence of dipole relaxation process. The effect of substitution of rare earth element dysprosium （Dy） showed increase in er in all the samples prepared for different concentrations from 0.00 to 0.20. An explanation for high value of er for Dy modified 0.5BiFeO3-0.5PbTiO3 （0.5BF-0.5PT） compared to Gd modified 0.5BF-0.5PT was provided. The variation of AC conductivity with inverse temperature found to obey the Arrhenius equation and the composites showed negative temperature coefficient of resistance （NTCR） behavior. The activation energy was found to be in the range from 0.25 to 0.40 eV for all the studied samples.展开更多
A novel two-phase composite film is prepared by the solvent casting method employing poly（methyl methacrylate） （PMMA） as polymer matrix and bismuth ferrite （BFO） as ceramic filler. The surfaces of BFO are functi...A novel two-phase composite film is prepared by the solvent casting method employing poly（methyl methacrylate） （PMMA） as polymer matrix and bismuth ferrite （BFO） as ceramic filler. The surfaces of BFO are functionalized by proper hydroxylating agents to activate their chemical nature. The structural analysis of the composite films confirms that the composites made up of functionalized BFO （BFO-OH） have a distorted rhombohedral structure. The morphological analysis shows that BFO- OH particles are equally distributed over the polymer matrix. The -OH functionality of BFO-OH is confirmed by FTIR. The dielectric and electrical studies at a frequency range from 100 Hz to I MHz reveal that PMMA-（BFO-OH） composites have enhanced dielectric constant as well as electrical conductivities, much higher than that of unmodified composites. According to the ferroelectric measurement result, the hydroxylated composite film shows a superior ferroelectric behavior than that of the unmodified one, with a remanent polarization （2Pr） of 2.764μC/cm2,展开更多
The polycrystalline Na_(2)SmV_(5)O_(15)(NSV),a new member of the tungsten bronze(TB)family,was prepared by a mixed-oxide technique.The room-temperature X-ray diffraction(XRD)confirmed the formation of single phase com...The polycrystalline Na_(2)SmV_(5)O_(15)(NSV),a new member of the tungsten bronze(TB)family,was prepared by a mixed-oxide technique.The room-temperature X-ray diffraction(XRD)confirmed the formation of single phase compound with orthorhombic crystal structure.The scanning electron microscopy(SEM)analysis indicated that the compound has homogeneous micrograph with a uniform distribution of small grains over the entire surface of the sample.The analysis of impedance spectra of NSV in a low-temperature range(-100℃to 100℃)at different frequencies exhibited interesting electrical properties like the contribution of bulk effect in conduction process.The study of imaginary part of the impedance at different temperatures showed existence of relaxation peak with its shift towards higher frequency on increasing temperature.This suggested the presence of frequency and temperature dependent relaxation process in the material.The loss peak spectra were found to abide by Arrhenius law with small activation energy of 0.12 eV.The temperature dependence of AC and DC electrical conductivity(σ_(AC) and σ_(DC))was also obtained.展开更多
The polycrystalline sample of LiSr2Nb5O15(LSN)was prepared by a high-temperature solid state reaction technique.The impedance parameters were studied using an impedance analyzer in a wide range of frequencies(102-106 ...The polycrystalline sample of LiSr2Nb5O15(LSN)was prepared by a high-temperature solid state reaction technique.The impedance parameters were studied using an impedance analyzer in a wide range of frequencies(102-106 Hz)at different temperatures(28-500℃).Nyquist plot reveals the presence of bulk effect only.The bulk resistance of the compound decreases with rise in temperature which shows the negative temperature coefficient of resistance(NTCR)like a semiconductor.The ac conductivity spectrum was found to obey Jonscher’s universal power law.DC conductivity(bulk)with temperature demonstrates that the compound exhibits Arrhenius type of electrical conductivity and the activation energy found to be 0.97 eV.展开更多
Polycrystalline samples of Bi_(1-x)La_(x)FeO_(3)[x=0.5,0.6,0.7 and 0.8]were synthesized through high temperature solid state reaction method.The structural studies of the compounds were done using X-ray diffraction te...Polycrystalline samples of Bi_(1-x)La_(x)FeO_(3)[x=0.5,0.6,0.7 and 0.8]were synthesized through high temperature solid state reaction method.The structural studies of the compounds were done using X-ray diffraction technique.Dielectric constant and dielectric loss were studied for various frequencies(100 Hz–10^(4)Hz)at different temperatures.The temperature-dependent non-Debye type relaxation process was suggested in the materials from the analysis of frequency-dependent electrical data at different temperatures.Temperature dependence of dc and ac conductivity at various frequencies showed negative temperature coefficient of resistance(NTCR)behavior.The frequency dependence of ac conductivity at different temperatures obeyed Jonscher’s universal power law.The temperature dependence of dc and ac conductivity was fitted to Arrhenius equation.The activation energies at different temperature ranges were calculated to know the charge species involved in the conduction process.展开更多
The Lanthanum-doped bismuth ferrite–lead titanate compositions of 0.5（Bi LaxFe1-xO3）–0.5（Pb Ti O3）（x = 0.05,0.10,0.15,0.20）（BLxF1-x-PT） were prepared by mixed oxide method.Structural characterization was per...The Lanthanum-doped bismuth ferrite–lead titanate compositions of 0.5（Bi LaxFe1-xO3）–0.5（Pb Ti O3）（x = 0.05,0.10,0.15,0.20）（BLxF1-x-PT） were prepared by mixed oxide method.Structural characterization was performed by X-ray diffraction and shows a tetragonal structure at room temperature.The lattice parameter c/a ratio decreases with increasing of La（x = 0.05–0.20） concentration of the composites.The effect of charge carrier/ion hopping mechanism,conductivity,relaxation process and impedance parameters was studied using an impedance analyzer in a wide frequency range（102–106Hz） at different temperatures.The nature of Nyquist plot confirms the presence of bulk effects only,and non-Debye type of relaxation processes occurs in the composites.The electrical modulus exhibits an important role of the hopping mechanism in the electrical transport process of the materials.The ac conductivity and dc conductivity of the materials were studied,and the activation energy found to be 0.81,0.77,0.76 and 0.74 e V for all compositions of x = 0.05–0.20 at different temperatures（200–300 ℃）.展开更多
In the present research work,frequency dependent electrical properties of tungsten bronze structured compounds Na2Pb2R2W2Ti4Nb4O30(R=Nd,Sm)are reported.X-ray diffraction(XRD)study of polycrystalline ceramic samples co...In the present research work,frequency dependent electrical properties of tungsten bronze structured compounds Na2Pb2R2W2Ti4Nb4O30(R=Nd,Sm)are reported.X-ray diffraction(XRD)study of polycrystalline ceramic samples confirms the formation of compounds with orthorhombic structure.Analysis of frequency dependent electrical data in the framework of modulus and conductivity formalism suggests the presence of thermally activated relaxation process in the compounds,which show Arrhenius behavior.The magnitudes of activation energies give the nature of the relaxing species.The real and imaginary parts of complex modulus trace the depressed semicircle in complex plane,suggesting non-Debye type relaxation process in the materials.The power law behavior of admittance data is successfully modeled by introducing constant phase element(CPE)to the equivalent circuit.A large value of power law parameter(n)of CPE below ferroelectric transition temperature(Tc)is attributed to the cooperative response of the dipoles which is reduced above Tc.This behavior is correlated with the frequency dependence of CPE,suggesting a physical meaning to it.The frequency dependent AC conductivity at different temperatures follows Jonscher’s universal power law.Almond and West formalism is used to estimate the hopping rate,activation enthalpy and charge carrier concentration in the materials.展开更多
(1-y)(BiFe_(1-x)GdxO_(3))–y(PbZrO3)composites(y=0:5),having four different Gd concentrations(x=0:05,0.1,0.15,and 0.2),were synthesized and their structural,dielectric,and ferroelectric properties have been studied us...(1-y)(BiFe_(1-x)GdxO_(3))–y(PbZrO3)composites(y=0:5),having four different Gd concentrations(x=0:05,0.1,0.15,and 0.2),were synthesized and their structural,dielectric,and ferroelectric properties have been studied using different characterization techniques.In addition,to investigate the effect of ion implantation on the microstructure and dielectric properties,these composites were exposed to 2 MeV He+-ions.Modifications of the structure,surface morphology and electrical properties of the samples before and after ion exposure were demonstrated using powder X-ray diffraction(XRD),scanning electron microscopy(SEM)technique,and LCR meter.The compositional analysis was carried out using energy dispersive X-ray spectrometry(EDS).XRD results demonstrated a decrease in the intensity profile of the dominant peak by a factor of 6 showing a degradation of the crystallinity.Willliamson–Hall(WH)plots reveal reduction in the grain size after irradiation along with an increase in strain and dislocation density.A decrease in the dielectric constant and loss has been recorded after ion beam exposure with reduction in ac conductivity value.The contribution of grain and grain boundary effect in conduction mechanism has been addressed using Nyquist plots.All the samples demonstrate a lossy ferroelectric loop which shows a clear modification upon irradiation.The role of structural defects modifying the physical properties of the composite materials is discussed in this work.展开更多
The polycrystalline samples of 0.8BiSm_(x)Fe_(1-x)O_(3)–0.2PbTiO_(3)(x=0.05;0.10;0.15 and 0.20)were prepared by using the conventional solid-state reaction technique and sintered at high temperature(850℃).X-ray diff...The polycrystalline samples of 0.8BiSm_(x)Fe_(1-x)O_(3)–0.2PbTiO_(3)(x=0.05;0.10;0.15 and 0.20)were prepared by using the conventional solid-state reaction technique and sintered at high temperature(850℃).X-ray diffraction(XRD)confirms the distorted rhombohedral crystal structure for all the composites at room temperature.The surface morphology was checked by field-emission scanning electron microscope(FESEM)technique and homogeneous mixing of the components was confirmed by energydispersive analysis of X-ray(EDAX).The detailed study of dielectric properties of the composites reveals an increasing nature of dielectric constant(ε_(r))and loss tangent(tanδ)with the increase of temperature due to thermal activation.The Arrhenius plots of temperature dependence of AC conductivity yield the activation energy within the material at high-temperature range.The ferroelectric study shows that the remnant polarization decreases with the increase of Samarium(Sm)concentration.展开更多
基金the SERB under DST Fast Track Scheme for Young Scientist (Project No. SR/FTP/PS-036/2011) New Delhi, IndiaCSIR for sanction of Emeritus Scientist scheme (Project No. 21(0944)/12/EMR-II)
文摘0.5BiDyxFe1-xO3-0.5PbTiOa（0.5BDxF1-x-0.5PT） （x=0.00, 0.05, 0.10, 0.15, 0.20） multiferroic composites were pre- pared by conventional solid state reaction method. Structural characterization was performed by X-ray diffraction and the mate- rials showed tetragonal structure at room temperature. Surface morphology of the composites was studied by a scanning electron microscope （SEM）. Frequency and temperature dependence of dielectric constant （er） and dielectric loss （tan~） of 0.5BDxF1_x- 0.5PT were measured in a wide range of frequency （100 Hz to 1 MHz） and temperature （25 to 400 ~C）. The analysis of the study showed that the er and tang decreased with increasing frequency in the given range for all the samples which could be explained through the occurrence of dipole relaxation process. The effect of substitution of rare earth element dysprosium （Dy） showed increase in er in all the samples prepared for different concentrations from 0.00 to 0.20. An explanation for high value of er for Dy modified 0.5BiFeO3-0.5PbTiO3 （0.5BF-0.5PT） compared to Gd modified 0.5BF-0.5PT was provided. The variation of AC conductivity with inverse temperature found to obey the Arrhenius equation and the composites showed negative temperature coefficient of resistance （NTCR） behavior. The activation energy was found to be in the range from 0.25 to 0.40 eV for all the studied samples.
文摘A novel two-phase composite film is prepared by the solvent casting method employing poly（methyl methacrylate） （PMMA） as polymer matrix and bismuth ferrite （BFO） as ceramic filler. The surfaces of BFO are functionalized by proper hydroxylating agents to activate their chemical nature. The structural analysis of the composite films confirms that the composites made up of functionalized BFO （BFO-OH） have a distorted rhombohedral structure. The morphological analysis shows that BFO- OH particles are equally distributed over the polymer matrix. The -OH functionality of BFO-OH is confirmed by FTIR. The dielectric and electrical studies at a frequency range from 100 Hz to I MHz reveal that PMMA-（BFO-OH） composites have enhanced dielectric constant as well as electrical conductivities, much higher than that of unmodified composites. According to the ferroelectric measurement result, the hydroxylated composite film shows a superior ferroelectric behavior than that of the unmodified one, with a remanent polarization （2Pr） of 2.764μC/cm2,
文摘The polycrystalline Na_(2)SmV_(5)O_(15)(NSV),a new member of the tungsten bronze(TB)family,was prepared by a mixed-oxide technique.The room-temperature X-ray diffraction(XRD)confirmed the formation of single phase compound with orthorhombic crystal structure.The scanning electron microscopy(SEM)analysis indicated that the compound has homogeneous micrograph with a uniform distribution of small grains over the entire surface of the sample.The analysis of impedance spectra of NSV in a low-temperature range(-100℃to 100℃)at different frequencies exhibited interesting electrical properties like the contribution of bulk effect in conduction process.The study of imaginary part of the impedance at different temperatures showed existence of relaxation peak with its shift towards higher frequency on increasing temperature.This suggested the presence of frequency and temperature dependent relaxation process in the material.The loss peak spectra were found to abide by Arrhenius law with small activation energy of 0.12 eV.The temperature dependence of AC and DC electrical conductivity(σ_(AC) and σ_(DC))was also obtained.
基金The authors(PN and BB)acknowledge the financial support through DRS-I under SAP of UGC for the development of research work in the School of Physics,SU.
文摘The polycrystalline sample of LiSr2Nb5O15(LSN)was prepared by a high-temperature solid state reaction technique.The impedance parameters were studied using an impedance analyzer in a wide range of frequencies(102-106 Hz)at different temperatures(28-500℃).Nyquist plot reveals the presence of bulk effect only.The bulk resistance of the compound decreases with rise in temperature which shows the negative temperature coefficient of resistance(NTCR)like a semiconductor.The ac conductivity spectrum was found to obey Jonscher’s universal power law.DC conductivity(bulk)with temperature demonstrates that the compound exhibits Arrhenius type of electrical conductivity and the activation energy found to be 0.97 eV.
文摘Polycrystalline samples of Bi_(1-x)La_(x)FeO_(3)[x=0.5,0.6,0.7 and 0.8]were synthesized through high temperature solid state reaction method.The structural studies of the compounds were done using X-ray diffraction technique.Dielectric constant and dielectric loss were studied for various frequencies(100 Hz–10^(4)Hz)at different temperatures.The temperature-dependent non-Debye type relaxation process was suggested in the materials from the analysis of frequency-dependent electrical data at different temperatures.Temperature dependence of dc and ac conductivity at various frequencies showed negative temperature coefficient of resistance(NTCR)behavior.The frequency dependence of ac conductivity at different temperatures obeyed Jonscher’s universal power law.The temperature dependence of dc and ac conductivity was fitted to Arrhenius equation.The activation energies at different temperature ranges were calculated to know the charge species involved in the conduction process.
基金support through DRS-I of UGC under SAP,School of Physics,Sambalpur University,UGC-Rajiv Gandhi National Fellowship scheme,UGCBSR fellowship scheme,SERB under DST Fast Track Scheme for Young Scientist (Project No.SR/FTP/PS-036/2011)New Delhi,India,and CSIR for sanction of Emeritus Scientist scheme (Project No.21(0944)/12/EMR-Ⅱ)
文摘The Lanthanum-doped bismuth ferrite–lead titanate compositions of 0.5（Bi LaxFe1-xO3）–0.5（Pb Ti O3）（x = 0.05,0.10,0.15,0.20）（BLxF1-x-PT） were prepared by mixed oxide method.Structural characterization was performed by X-ray diffraction and shows a tetragonal structure at room temperature.The lattice parameter c/a ratio decreases with increasing of La（x = 0.05–0.20） concentration of the composites.The effect of charge carrier/ion hopping mechanism,conductivity,relaxation process and impedance parameters was studied using an impedance analyzer in a wide frequency range（102–106Hz） at different temperatures.The nature of Nyquist plot confirms the presence of bulk effects only,and non-Debye type of relaxation processes occurs in the composites.The electrical modulus exhibits an important role of the hopping mechanism in the electrical transport process of the materials.The ac conductivity and dc conductivity of the materials were studied,and the activation energy found to be 0.81,0.77,0.76 and 0.74 e V for all compositions of x = 0.05–0.20 at different temperatures（200–300 ℃）.
文摘In the present research work,frequency dependent electrical properties of tungsten bronze structured compounds Na2Pb2R2W2Ti4Nb4O30(R=Nd,Sm)are reported.X-ray diffraction(XRD)study of polycrystalline ceramic samples confirms the formation of compounds with orthorhombic structure.Analysis of frequency dependent electrical data in the framework of modulus and conductivity formalism suggests the presence of thermally activated relaxation process in the compounds,which show Arrhenius behavior.The magnitudes of activation energies give the nature of the relaxing species.The real and imaginary parts of complex modulus trace the depressed semicircle in complex plane,suggesting non-Debye type relaxation process in the materials.The power law behavior of admittance data is successfully modeled by introducing constant phase element(CPE)to the equivalent circuit.A large value of power law parameter(n)of CPE below ferroelectric transition temperature(Tc)is attributed to the cooperative response of the dipoles which is reduced above Tc.This behavior is correlated with the frequency dependence of CPE,suggesting a physical meaning to it.The frequency dependent AC conductivity at different temperatures follows Jonscher’s universal power law.Almond and West formalism is used to estimate the hopping rate,activation enthalpy and charge carrier concentration in the materials.
基金Thomas Osipowicz,National University of Singapore for extending access to the accelerator facility.The author,P.Nayak,acknowledges CSIR for sanction of the Emeritus Scientist scheme(Project No.21(0944)/12/EMR-II)One of the authors,B.Behera,acknowledges the SERB under the DST Fast Track Scheme for Young Scientists(Project No.SR/FTP/PS-036/2011)New Delhi,India.
文摘(1-y)(BiFe_(1-x)GdxO_(3))–y(PbZrO3)composites(y=0:5),having four different Gd concentrations(x=0:05,0.1,0.15,and 0.2),were synthesized and their structural,dielectric,and ferroelectric properties have been studied using different characterization techniques.In addition,to investigate the effect of ion implantation on the microstructure and dielectric properties,these composites were exposed to 2 MeV He+-ions.Modifications of the structure,surface morphology and electrical properties of the samples before and after ion exposure were demonstrated using powder X-ray diffraction(XRD),scanning electron microscopy(SEM)technique,and LCR meter.The compositional analysis was carried out using energy dispersive X-ray spectrometry(EDS).XRD results demonstrated a decrease in the intensity profile of the dominant peak by a factor of 6 showing a degradation of the crystallinity.Willliamson–Hall(WH)plots reveal reduction in the grain size after irradiation along with an increase in strain and dislocation density.A decrease in the dielectric constant and loss has been recorded after ion beam exposure with reduction in ac conductivity value.The contribution of grain and grain boundary effect in conduction mechanism has been addressed using Nyquist plots.All the samples demonstrate a lossy ferroelectric loop which shows a clear modification upon irradiation.The role of structural defects modifying the physical properties of the composite materials is discussed in this work.
基金One of the authors(Truptimayee Sahu)acknowledges the financial support through DST-INSPIRE Fellowship to carry out the research work.The author also acknowledges the financial support through DRS-1 of UGC,New Delhi,India,under the SAP and FIST Programmes of DST,New Delhi,India,for the development of research work at School of Physics,Sambalpur University,Odisha.One of the authors(B.Behera)acknowledges the SERB,New Delhi,India,under DST Fast Track Scheme for Young Scientist(Project No.SR/FTP/PS-036/2011).
文摘The polycrystalline samples of 0.8BiSm_(x)Fe_(1-x)O_(3)–0.2PbTiO_(3)(x=0.05;0.10;0.15 and 0.20)were prepared by using the conventional solid-state reaction technique and sintered at high temperature(850℃).X-ray diffraction(XRD)confirms the distorted rhombohedral crystal structure for all the composites at room temperature.The surface morphology was checked by field-emission scanning electron microscope(FESEM)technique and homogeneous mixing of the components was confirmed by energydispersive analysis of X-ray(EDAX).The detailed study of dielectric properties of the composites reveals an increasing nature of dielectric constant(ε_(r))and loss tangent(tanδ)with the increase of temperature due to thermal activation.The Arrhenius plots of temperature dependence of AC conductivity yield the activation energy within the material at high-temperature range.The ferroelectric study shows that the remnant polarization decreases with the increase of Samarium(Sm)concentration.
