Development and application of ferrite materials for low temperature co-fired ceramic （LTCC） technology are dis- cussed, specifically addressing several typical ferrite materials such as M-type barium ferrite, NiCuZ...Development and application of ferrite materials for low temperature co-fired ceramic （LTCC） technology are dis- cussed, specifically addressing several typical ferrite materials such as M-type barium ferrite, NiCuZn ferrite, YIG ferrite, and lithium ferrite. In order to permit co-firing with a silver internal electrode in LTCC process, the sintering temperature of ferrite materials should be less than 950 ℃. These ferrite materials are research focuses and are applied in many ways in electronics.展开更多
In near-field communication(NFC)antennas,soft magnetic ferrites are usually applied as a substrate to reduce eddy current loss and increase magnetic field coupling.For this purpose,the applied ferrites are required to...In near-field communication(NFC)antennas,soft magnetic ferrites are usually applied as a substrate to reduce eddy current loss and increase magnetic field coupling.For this purpose,the applied ferrites are required to have high permeability and saturation magnetization together with low magnetic loss and dielectric loss.However,for most soft magnetic ferrites,it is difficult to meet all the requirements.Herein novel Ni-Zn ferrite ceramics co-doped by Ho^(3+)and Co^(2+)ions with chemical formula Ni_(0.5-x)Zn_(0.5)Ho_(0.02)Co_(x)Fe_(1.98)O_(4)(x=0-0.2)were designed and prepared to balance these needs on the basis of molten salt synthesis with metal nitrates as raw materials and potassium hydroxide(KOH)as the precipitation agent and molten salt precursor.After the substitution of Ho^(3+),the saturation magnetization and initial permeability decrease,but with further doping of Co^(2+),the saturation magnetization gradually increases,while the initial permeability continues to decrease.When x=0.1,the sample will have the lowest dielectric constant,magnetic and dielectric loss,as well as the highest Curie temperature(305℃).Moreover,the acquired Ni-Zn ferrites have been applied simulatively in NFC antennas,revealing that the device manufactured with the optimal Ni_(0.4)Zn_(0.5)Ho_(0.02)Co_(0.1)Fe_(1.98)O_(4)ferrite ceramics would have significantly improved performance at 13.56 MHz with low leakage and long transmit distance of magnetic field.Therefore,the Ni_(0.4)Zn_(0.5)Ho_(0.02)Co_(0.1)Fe_(1.98)O_(4)ferrite ceramics would be a good candidate for NFC antenna substrates.展开更多
Co_((1-x))ZnxFe_(2)O_(4)nanospheres(x=0,0.5,0.8)with a unidirectional cubic spinel structure were prepared by a solvothermal method.By using a range of theoretical and empirical models,the experimental heat capacity v...Co_((1-x))ZnxFe_(2)O_(4)nanospheres(x=0,0.5,0.8)with a unidirectional cubic spinel structure were prepared by a solvothermal method.By using a range of theoretical and empirical models,the experimental heat capacity values were fitted as a function of temperature over a suitable temperature range to explain the possible relationship between the magnetic properties and microstructure of the nanospheres.As a result,at a low temperature(T<10 K),the parameter Bfswdecreases with increasing Zn concentration,implying that the exchange interaction between A and B sites decreases.At a relatively high temperature(T>50 K),the Debye temperature decreases with increasing Zn concentration,which is due to the weakening of the interatomic bonding force after the addition of non-magnetic materials to the Co Fe_(2)O_(4)spinel ferrite.展开更多
CO2 is a major component of the greenhouse gases, which causes the global warming. To reduce CO2 gas, high activity nanosized Ni＋2 substituted Fe2TiO5 samples were synthesized by conventional ceramic method. The effe...CO2 is a major component of the greenhouse gases, which causes the global warming. To reduce CO2 gas, high activity nanosized Ni＋2 substituted Fe2TiO5 samples were synthesized by conventional ceramic method. The effect of the composition of the synthesized ferrite on the H2-reduction and CO2-catalytic decomposition was investigated. Fe2TiO5 （iron titanate） phase that has a nanocrystallite size of -80 nm is formed as a result of heating Fe2O3 and TiO2 while the addition of NiO leads to the formation of new phases （-80 nm） NiTiO3 and NiFe2O4, but the mixed solid of NiO and Fe2O3 results in the formation of NiFe2O4 only. Samples with Ni^＋2=0 shows the lowest reduction extent （20%）; as the extent of Ni＋2 increases, the extent of reduction increases. The increase in the reduction percent is attributed to the presence of NiTiO3 and NiFe2O4 phases, which are more reducible phases than Fe2TiO5. The CO2 decomposition reactions were monitored by thermogravimetric analysis （TGA） experiments. The oxidation of the H2-reduced Ni＋2 substituted Fe2TiO5 at 500℃ was investigated. As Ni^＋2 increases, the rate of reoxidation increases. Samples with the highest reduction extents gave the highest reoxidation extent, which is attributed to the highly porous nature and deficiency in oxygen due to the presence of metallic Fe, Ni and/or FeNi alloy. X-ray diffraction （XRD） and transmission electron microscopy （TEM） of oxidized samples show also the presence of carbon in the sample containing Ni＋2〉0, which appears in the form of nanotubes （25 nm）.展开更多
Nanosized Co_(0.5)Zn_(0.5)Fe_(2)O_(4) ferrite was prepared by chemical co-precipitation method.The samples were characterized by X-ray diffraction(XRD),field-emission transmission electron microscopy(FETEM),vibrating ...Nanosized Co_(0.5)Zn_(0.5)Fe_(2)O_(4) ferrite was prepared by chemical co-precipitation method.The samples were characterized by X-ray diffraction(XRD),field-emission transmission electron microscopy(FETEM),vibrating sample magnetometer(VSM)and network analyzer.TEM analysis indicates that the diameter of as-prepared powder is about 20-30 nm.The saturation magnetization of nanosized Co_(0.5)Zn_(0.5)Fe_(2)O_(4) ferrite is 74.01 mA·m^(2)·g^(−1).The complex permittivity and complex permeability of the Co-Zn ferrite were measured by vector network analyzer in the frequency range of 2.0-18.0 GHz,and the reflection loss(RL)was investigated according to the wave transmission theory.The results show that the maximum reflection loss reaches−13.7 dB at 6.8 GHz and the bandwidth of reflection loss less than−10 dB reaches 3.8 GHz.The as-prepared nanosized Co_(0.5)Zn_(0.5)Fe_(2)O_(4) ferrite can be potentially used as an excellent microwave absorber in the C-band.展开更多
Oxalate was generally used as a precipitant for synthesis of MnZn ferrites during the co-precipitation process. However, the MnZn ferrite couldn’t be directly obtained and a calcination process was needed. In this re...Oxalate was generally used as a precipitant for synthesis of MnZn ferrites during the co-precipitation process. However, the MnZn ferrite couldn’t be directly obtained and a calcination process was needed. In this research, we reported a direct preparation of the MnZn ferrite nanoparticles by using co-precipitation method, together with refluxing process. XRD measurements proved that crystallite size of the obtained samples increased with an increase in pH value of the co-precipitation solution, and that the crystallite size of about 25 nm was obtained for the sample at a pH of 13. This sample showed the maximum Ms of 58.6 emu/g, which was about one times larger than that of 12 (pH value). Calcination to the obtained samples result in an enlargement in their crystal size and an improvement in their magnetic properties with an increase in temperatures. The samples calcinated in CO2 + H2 atmosphere presented good stability, and the maximum Ms value of 188.2 emu/g was obtained for the 1100。C-heated sample. Unfortunately, precipitation of some Fe2O3 at 800。C suggested poor stability of the nanocrystalline MnZn ferrite in N2 atmosphere.展开更多
In this study, nanocrystalline Co-Ni-Mg ferrite powders with composition Coo.5Nio.5-xMgxFe2O4 are successfully synthesized by the co-precipitation method. A systematic investigation on the structural, morphological an...In this study, nanocrystalline Co-Ni-Mg ferrite powders with composition Coo.5Nio.5-xMgxFe2O4 are successfully synthesized by the co-precipitation method. A systematic investigation on the structural, morphological and magnetic properties of un-doped and Mg-doped Co-Ni ferrite nanoparticles is carried out. The prepared samples are characterized using x-ray diffraction （XRD） analysis, Fourier transform infrared spectroscopy （FTIR）, field emission scanning electron microscopy （FESEM）, and vibrating sample magnetometry （VSM）. The XRD analyses of the synthesized samples confirm the formation of single-phase cubic spinel structures with crystallite sizes in a range of - 32 nm to - 36 nm. The lat- tice constant increases with increasing Mg content. FESEM images show that the synthesized samples are homogeneous with a uniformly distributed grain. The results of IR spectroscopy analysis indicate the formation of functional groups of spinel ferrite in the co-precipitation process. By increasing Mg2- substitution, room temperature magnetic measurement shows that maximum magnetization and coercivity increase from - 57.35 emu/g to - 61.49 emu/g and - 603.26 Oe to 684.11 Oe （l Oe = 79.5775 A.m-l）, respectively. The higher values of magnetization Ms and Mr suggest that the opti- mum composition is Co0.5Ni0.4Mg0.1Fe204 that can be applied to high-density recording media and microwave devices.展开更多
Fe2O3, TiO2, CuO and ZnO powders were mixed according to the formula of （1-x）TiO2 xCuO-Fe2O3 or （1-x）TiO2 xZnO-Fe2O3 （x=0, 0.2 0.4, 0.6, 0.8, 1）, and well ball-milled with H2O for 3 h to ensure homogeneity of th...Fe2O3, TiO2, CuO and ZnO powders were mixed according to the formula of （1-x）TiO2 xCuO-Fe2O3 or （1-x）TiO2 xZnO-Fe2O3 （x=0, 0.2 0.4, 0.6, 0.8, 1）, and well ball-milled with H2O for 3 h to ensure homogeneity of the powdered solids, then fired at 1200℃ for 4 h. The fired samples were reduced at 500℃ with hydrogen gas. The reduced samples were subjected to recalcination at 500℃ in CO2 atmosphere. Both of fired, reduced and calcined samples were characterized by X-ray diffraction, vibrating sample magnetometry, reflected light microscopy and scanning electron microscopy. Different phases were formed after firing of Cu^＋2 or Zn^2＋ substituted Fe2TiO5. Magnetization （Bs） of the formed phases after firing are very low corresponding to diluted magnetic semiconductors （DMS） and increases with increasing the substituted cations （Cu^＋2 or Zn^2＋）. The reduction of the fired samples enhanced the Bs values whereas the reducibility increases with increasing the Cu^＋2 or Zn^2＋ content. Samples show different tendency toward CO2 decomposition which is very important for environmental minimization for CO2.展开更多
Spinel ferrites have a significant role in high-tech applications.In the present work nano-crystalline ferrites having general formula Co0.5Cd0.5BixFe2-xO4 with(x=0.0,0.05,0.1,0.15,0.2,and 0.25)are synthesized via mic...Spinel ferrites have a significant role in high-tech applications.In the present work nano-crystalline ferrites having general formula Co0.5Cd0.5BixFe2-xO4 with(x=0.0,0.05,0.1,0.15,0.2,and 0.25)are synthesized via micro-emulsion route.Powder x-ray diffraction(XRD)studies discover the FCC spinel structure.Crystalline size is calculated in a range of 11 nm-15 nm.Lattice parameter calculations are reduced due to its substitution which leads to the exchange of large ionic radius of Fe^3+for small ionic radius of Bi^3+.The x-ray density is analyzed to increase with doping.Fourier transform infrared spectroscopy(FTIR)is performed to analyze absorption band spectra.The two absorption bands are observed in a range of 400 cm^-1-600 cm^-1,and they are the characteristic feature of spinel structure.Thermo-gravimetric analysis(TGA)reveals the total weight loss of nearly 1.98%.Dielectric analysis is carried out by impedance analyzer in a frequency span from 1 MHz to 3 GHz by using the Maxwell Wagner model.Dielectric studies reveal the decrease of dielectric parameters.The alternating current(AC)conductivity exhibits a plane behavior in a low frequency range and it increases with the applied frequency increasing.This is attributed to the grain effects in a high frequency range or may be due to the reduction of porosity.Real and imaginary part of impedance show the decreasing trend which corresponds to the grain boundary action.The imaginary modulus shows the occurrence of peak that helps to understand the interfacial polarization.Cole-Cole graph shows a single semicircle which confirms that the conduction mechanism is due to the grain boundaries at low frequency.Dielectric studies reveal the applicability of these ferrites in high frequency equipment,microwave applications,high storage media,and semiconductor devices.展开更多
A systematic study on the influence of Nd^(3+) substitution on structural,magnetic and electrical properties of cobalt ferrite nanopowders obtained by sol–gel auto-combustion routewas reported.The formation of spinel...A systematic study on the influence of Nd^(3+) substitution on structural,magnetic and electrical properties of cobalt ferrite nanopowders obtained by sol–gel auto-combustion routewas reported.The formation of spinel phasewas confirmed by X-ray diffraction(XRD)data,and percolation limit ofNd3?into the spinel lattice was also observed.Fourier transform infrared spectroscopy(FTIR)bands observed ≈580 and ≈390 cm^(-1 ) support the presence of Fe^(3+) at A andBsites in the spinel lattice.The variation in microstructure was investigated by scanning electronmicroscopy(SEM),and the average grain size varies from 5.3 to 3.3 lm.The substitution of Nd^(3+) significantly affects the formation of pores and grain size of cobalt ferrite.Room-temperature saturation magnetization and coercivity decrease from 60 to 30 mA·m^(2)·g^(-1) and 19.9–17.8 mT,respectively,with Nd^(3+) substitution increasing.These decreases in magnetic properties are explained based on the presence of non-magnetic nature of Nd^(3+) concentration and the dilution of super-exchange interaction in the spinel lattice.The room-temperature direct-current electrical resistivity increases with Nd^(3+) concentration increasing,which is due to the unavailability of Fe^(2+) at octahedral B sites.展开更多
Chemical looping technology holds great potential on efficient CO2 splitting with much higher CO production and CO2 splitting rate than photocatalytic processes.Conventional oxygen carrier requires high temperature(ty...Chemical looping technology holds great potential on efficient CO2 splitting with much higher CO production and CO2 splitting rate than photocatalytic processes.Conventional oxygen carrier requires high temperature(typically 850–1000°C)to ensure sufficient redox activity,but the stable and high CO2 conversion is favored at a lower temperature,leading to the degrading on the reaction kinetics as well as the low CO production and CO2 splitting rate.In this paper,we prepared several ternary spinels and demonstrated their performance for chemical looping CO2 splitting at moderate temperatures.Using the promotion effect of Cu to cobalt ferrite reduction and reversible phase change of the reduced metals,Cu0.4 Co0.6 Fe2 O4 exhibits high CO2 splitting rate(144.6μmol g–1 min–1)and total CO production(9100μmol g–1)at 650°C.The high performance of this earth-abundant spinel material is also consistent in repeated redox cycles,enabling their potential in industrial use.展开更多
基金Project supported by the National Basic Research Program of China(Grant No.2012CB933100)the National Natural Science Foundation of China(Grant Nos.51132003,61021061,and 61171047)the Second Item of Strongpoint Industry of Guangdong Province,China(Grant No.2012A090100001)
文摘Development and application of ferrite materials for low temperature co-fired ceramic （LTCC） technology are dis- cussed, specifically addressing several typical ferrite materials such as M-type barium ferrite, NiCuZn ferrite, YIG ferrite, and lithium ferrite. In order to permit co-firing with a silver internal electrode in LTCC process, the sintering temperature of ferrite materials should be less than 950 ℃. These ferrite materials are research focuses and are applied in many ways in electronics.
基金This work was supported by the National Natural Science Foundation of China(Nos.11674035 and 61274015)the Fundamental Research Funds for the Central Universities.
文摘In near-field communication(NFC)antennas,soft magnetic ferrites are usually applied as a substrate to reduce eddy current loss and increase magnetic field coupling.For this purpose,the applied ferrites are required to have high permeability and saturation magnetization together with low magnetic loss and dielectric loss.However,for most soft magnetic ferrites,it is difficult to meet all the requirements.Herein novel Ni-Zn ferrite ceramics co-doped by Ho^(3+)and Co^(2+)ions with chemical formula Ni_(0.5-x)Zn_(0.5)Ho_(0.02)Co_(x)Fe_(1.98)O_(4)(x=0-0.2)were designed and prepared to balance these needs on the basis of molten salt synthesis with metal nitrates as raw materials and potassium hydroxide(KOH)as the precipitation agent and molten salt precursor.After the substitution of Ho^(3+),the saturation magnetization and initial permeability decrease,but with further doping of Co^(2+),the saturation magnetization gradually increases,while the initial permeability continues to decrease.When x=0.1,the sample will have the lowest dielectric constant,magnetic and dielectric loss,as well as the highest Curie temperature(305℃).Moreover,the acquired Ni-Zn ferrites have been applied simulatively in NFC antennas,revealing that the device manufactured with the optimal Ni_(0.4)Zn_(0.5)Ho_(0.02)Co_(0.1)Fe_(1.98)O_(4)ferrite ceramics would have significantly improved performance at 13.56 MHz with low leakage and long transmit distance of magnetic field.Therefore,the Ni_(0.4)Zn_(0.5)Ho_(0.02)Co_(0.1)Fe_(1.98)O_(4)ferrite ceramics would be a good candidate for NFC antenna substrates.
基金Basic Research Project of Liaoning Provincial Department of Education(No.LJKMZ20220829)Guangxi Key Laboratory of Information Materials(Guilin University of Electronic Technology)(No.211006-K)。
文摘Co_((1-x))ZnxFe_(2)O_(4)nanospheres(x=0,0.5,0.8)with a unidirectional cubic spinel structure were prepared by a solvothermal method.By using a range of theoretical and empirical models,the experimental heat capacity values were fitted as a function of temperature over a suitable temperature range to explain the possible relationship between the magnetic properties and microstructure of the nanospheres.As a result,at a low temperature(T<10 K),the parameter Bfswdecreases with increasing Zn concentration,implying that the exchange interaction between A and B sites decreases.At a relatively high temperature(T>50 K),the Debye temperature decreases with increasing Zn concentration,which is due to the weakening of the interatomic bonding force after the addition of non-magnetic materials to the Co Fe_(2)O_(4)spinel ferrite.
文摘CO2 is a major component of the greenhouse gases, which causes the global warming. To reduce CO2 gas, high activity nanosized Ni＋2 substituted Fe2TiO5 samples were synthesized by conventional ceramic method. The effect of the composition of the synthesized ferrite on the H2-reduction and CO2-catalytic decomposition was investigated. Fe2TiO5 （iron titanate） phase that has a nanocrystallite size of -80 nm is formed as a result of heating Fe2O3 and TiO2 while the addition of NiO leads to the formation of new phases （-80 nm） NiTiO3 and NiFe2O4, but the mixed solid of NiO and Fe2O3 results in the formation of NiFe2O4 only. Samples with Ni^＋2=0 shows the lowest reduction extent （20%）; as the extent of Ni＋2 increases, the extent of reduction increases. The increase in the reduction percent is attributed to the presence of NiTiO3 and NiFe2O4 phases, which are more reducible phases than Fe2TiO5. The CO2 decomposition reactions were monitored by thermogravimetric analysis （TGA） experiments. The oxidation of the H2-reduced Ni＋2 substituted Fe2TiO5 at 500℃ was investigated. As Ni^＋2 increases, the rate of reoxidation increases. Samples with the highest reduction extents gave the highest reoxidation extent, which is attributed to the highly porous nature and deficiency in oxygen due to the presence of metallic Fe, Ni and/or FeNi alloy. X-ray diffraction （XRD） and transmission electron microscopy （TEM） of oxidized samples show also the presence of carbon in the sample containing Ni＋2〉0, which appears in the form of nanotubes （25 nm）.
基金financially supported by the National Natural Science Foundation of China(Nos.51402154,51202111)the Natural Science Foundation of Jiangsu Province(No.BK20141000)+1 种基金the Natural Science Foundation of Jiangsu Provincial Universities(No.14KJB430019)the Priority Academic Program Development of Jiangsu Higher Education Institutions(PAPD)。
文摘Nanosized Co_(0.5)Zn_(0.5)Fe_(2)O_(4) ferrite was prepared by chemical co-precipitation method.The samples were characterized by X-ray diffraction(XRD),field-emission transmission electron microscopy(FETEM),vibrating sample magnetometer(VSM)and network analyzer.TEM analysis indicates that the diameter of as-prepared powder is about 20-30 nm.The saturation magnetization of nanosized Co_(0.5)Zn_(0.5)Fe_(2)O_(4) ferrite is 74.01 mA·m^(2)·g^(−1).The complex permittivity and complex permeability of the Co-Zn ferrite were measured by vector network analyzer in the frequency range of 2.0-18.0 GHz,and the reflection loss(RL)was investigated according to the wave transmission theory.The results show that the maximum reflection loss reaches−13.7 dB at 6.8 GHz and the bandwidth of reflection loss less than−10 dB reaches 3.8 GHz.The as-prepared nanosized Co_(0.5)Zn_(0.5)Fe_(2)O_(4) ferrite can be potentially used as an excellent microwave absorber in the C-band.
文摘Oxalate was generally used as a precipitant for synthesis of MnZn ferrites during the co-precipitation process. However, the MnZn ferrite couldn’t be directly obtained and a calcination process was needed. In this research, we reported a direct preparation of the MnZn ferrite nanoparticles by using co-precipitation method, together with refluxing process. XRD measurements proved that crystallite size of the obtained samples increased with an increase in pH value of the co-precipitation solution, and that the crystallite size of about 25 nm was obtained for the sample at a pH of 13. This sample showed the maximum Ms of 58.6 emu/g, which was about one times larger than that of 12 (pH value). Calcination to the obtained samples result in an enlargement in their crystal size and an improvement in their magnetic properties with an increase in temperatures. The samples calcinated in CO2 + H2 atmosphere presented good stability, and the maximum Ms value of 188.2 emu/g was obtained for the 1100。C-heated sample. Unfortunately, precipitation of some Fe2O3 at 800。C suggested poor stability of the nanocrystalline MnZn ferrite in N2 atmosphere.
基金supported by the Ibnu Sina Institute for Scientific and Industrial Research,Physics Department of Universiti Teknologi Malaysia and the Ministry of Education Malaysia(Grant Nos.Q.J130000.2526.04H65)
文摘In this study, nanocrystalline Co-Ni-Mg ferrite powders with composition Coo.5Nio.5-xMgxFe2O4 are successfully synthesized by the co-precipitation method. A systematic investigation on the structural, morphological and magnetic properties of un-doped and Mg-doped Co-Ni ferrite nanoparticles is carried out. The prepared samples are characterized using x-ray diffraction （XRD） analysis, Fourier transform infrared spectroscopy （FTIR）, field emission scanning electron microscopy （FESEM）, and vibrating sample magnetometry （VSM）. The XRD analyses of the synthesized samples confirm the formation of single-phase cubic spinel structures with crystallite sizes in a range of - 32 nm to - 36 nm. The lat- tice constant increases with increasing Mg content. FESEM images show that the synthesized samples are homogeneous with a uniformly distributed grain. The results of IR spectroscopy analysis indicate the formation of functional groups of spinel ferrite in the co-precipitation process. By increasing Mg2- substitution, room temperature magnetic measurement shows that maximum magnetization and coercivity increase from - 57.35 emu/g to - 61.49 emu/g and - 603.26 Oe to 684.11 Oe （l Oe = 79.5775 A.m-l）, respectively. The higher values of magnetization Ms and Mr suggest that the opti- mum composition is Co0.5Ni0.4Mg0.1Fe204 that can be applied to high-density recording media and microwave devices.
文摘Fe2O3, TiO2, CuO and ZnO powders were mixed according to the formula of （1-x）TiO2 xCuO-Fe2O3 or （1-x）TiO2 xZnO-Fe2O3 （x=0, 0.2 0.4, 0.6, 0.8, 1）, and well ball-milled with H2O for 3 h to ensure homogeneity of the powdered solids, then fired at 1200℃ for 4 h. The fired samples were reduced at 500℃ with hydrogen gas. The reduced samples were subjected to recalcination at 500℃ in CO2 atmosphere. Both of fired, reduced and calcined samples were characterized by X-ray diffraction, vibrating sample magnetometry, reflected light microscopy and scanning electron microscopy. Different phases were formed after firing of Cu^＋2 or Zn^2＋ substituted Fe2TiO5. Magnetization （Bs） of the formed phases after firing are very low corresponding to diluted magnetic semiconductors （DMS） and increases with increasing the substituted cations （Cu^＋2 or Zn^2＋）. The reduction of the fired samples enhanced the Bs values whereas the reducibility increases with increasing the Cu^＋2 or Zn^2＋ content. Samples show different tendency toward CO2 decomposition which is very important for environmental minimization for CO2.
基金the ORIC of Balochistan University of Information Technology Engineering and Management Sciences (BUITEMS) Quetta-PK, for help and financial support to accomplish this research work in the Department of Physics
文摘Spinel ferrites have a significant role in high-tech applications.In the present work nano-crystalline ferrites having general formula Co0.5Cd0.5BixFe2-xO4 with(x=0.0,0.05,0.1,0.15,0.2,and 0.25)are synthesized via micro-emulsion route.Powder x-ray diffraction(XRD)studies discover the FCC spinel structure.Crystalline size is calculated in a range of 11 nm-15 nm.Lattice parameter calculations are reduced due to its substitution which leads to the exchange of large ionic radius of Fe^3+for small ionic radius of Bi^3+.The x-ray density is analyzed to increase with doping.Fourier transform infrared spectroscopy(FTIR)is performed to analyze absorption band spectra.The two absorption bands are observed in a range of 400 cm^-1-600 cm^-1,and they are the characteristic feature of spinel structure.Thermo-gravimetric analysis(TGA)reveals the total weight loss of nearly 1.98%.Dielectric analysis is carried out by impedance analyzer in a frequency span from 1 MHz to 3 GHz by using the Maxwell Wagner model.Dielectric studies reveal the decrease of dielectric parameters.The alternating current(AC)conductivity exhibits a plane behavior in a low frequency range and it increases with the applied frequency increasing.This is attributed to the grain effects in a high frequency range or may be due to the reduction of porosity.Real and imaginary part of impedance show the decreasing trend which corresponds to the grain boundary action.The imaginary modulus shows the occurrence of peak that helps to understand the interfacial polarization.Cole-Cole graph shows a single semicircle which confirms that the conduction mechanism is due to the grain boundaries at low frequency.Dielectric studies reveal the applicability of these ferrites in high frequency equipment,microwave applications,high storage media,and semiconductor devices.
基金Authors would like to thank the management of Koneru Lakshmaiah Education Foundation for giving us the support and encouragement to do research.RAR,GKK,NKJ would like to thank Department of Science and Technology(DST),Govt.of India,for the award of DST-FIST Level-1(SR/FST/PS-1/2018/35)scheme to Department of Physics,KLEF.
文摘A systematic study on the influence of Nd^(3+) substitution on structural,magnetic and electrical properties of cobalt ferrite nanopowders obtained by sol–gel auto-combustion routewas reported.The formation of spinel phasewas confirmed by X-ray diffraction(XRD)data,and percolation limit ofNd3?into the spinel lattice was also observed.Fourier transform infrared spectroscopy(FTIR)bands observed ≈580 and ≈390 cm^(-1 ) support the presence of Fe^(3+) at A andBsites in the spinel lattice.The variation in microstructure was investigated by scanning electronmicroscopy(SEM),and the average grain size varies from 5.3 to 3.3 lm.The substitution of Nd^(3+) significantly affects the formation of pores and grain size of cobalt ferrite.Room-temperature saturation magnetization and coercivity decrease from 60 to 30 mA·m^(2)·g^(-1) and 19.9–17.8 mT,respectively,with Nd^(3+) substitution increasing.These decreases in magnetic properties are explained based on the presence of non-magnetic nature of Nd^(3+) concentration and the dilution of super-exchange interaction in the spinel lattice.The room-temperature direct-current electrical resistivity increases with Nd^(3+) concentration increasing,which is due to the unavailability of Fe^(2+) at octahedral B sites.
基金National Natural Science Foundation of China(Grant No.51706041)the National Natural Science Foundation of China(NSFC)Projects(Grant No.51661145011)the National Science Foundation for Distinguished Young Scholars of China(Grant No.51525601)。
文摘Chemical looping technology holds great potential on efficient CO2 splitting with much higher CO production and CO2 splitting rate than photocatalytic processes.Conventional oxygen carrier requires high temperature(typically 850–1000°C)to ensure sufficient redox activity,but the stable and high CO2 conversion is favored at a lower temperature,leading to the degrading on the reaction kinetics as well as the low CO production and CO2 splitting rate.In this paper,we prepared several ternary spinels and demonstrated their performance for chemical looping CO2 splitting at moderate temperatures.Using the promotion effect of Cu to cobalt ferrite reduction and reversible phase change of the reduced metals,Cu0.4 Co0.6 Fe2 O4 exhibits high CO2 splitting rate(144.6μmol g–1 min–1)and total CO production(9100μmol g–1)at 650°C.The high performance of this earth-abundant spinel material is also consistent in repeated redox cycles,enabling their potential in industrial use.
