Structural,dielectric and electrical properties of bismuth magnesium tantalate electronic system

The lead-free dielectric compound Bi(Mg2/3Ta1/3)O3(BMT)has been synthesized at high temperature by a low-cost solid-state method.The X-ray diffraction(XRD)technique reveals that the fabricated sample has an orthorhombic crystal system.The scanning electron microscope(SEM)image displays the uniform distribution of grains on the surface of the specimen.The dielectric parameters(permittivity(εr),and loss tangent(tanδ)are studied over a wide range of temperature(150-500℃)and frequency(1 kHz-1 MHz).The temperature dependent conductivity plot follows Universal Johnson’s power law.The complex impedance and modulus spectrum illustrate the electrical behavior of the compound at various frequency and temperature.The Nyquist spectra show the presence of the effect of grain and grain boundary in the synthesized compound.The grain resistance value declines with the rise in temperature that shows the presence of a negative temperature coefficient(NTCR)behavior in the compound.The complex modulus spectra display the occurrence of the conduction mechanism in the specimen.The reported compound has a relative dielectric constant and loss of 22×10^3 and 1.8 respectively at 1 kHz frequency and 500℃,thus becoming an efficient applicant for dielectric applications that can operate at higher temperatures.

Dielectric relaxation and magneto-electric characteristics of lead-free double perovskite: Sm2NiMnO6

The polycrystalline sample of a double perovskite, Sm2NiMnO6 was synthesized by a solid-state reaction route. From the X-ray structural study, it is found that the structure of the material is monoclinic with lattice parameters: a = 4.1750(63) ?, b = 7.6113(63) ?, c = 5.9896(63) ?, and β = 112.70°. These parameters are very close to and consistent with those of such type of materials. The dielectric, impedance, AC conductivity, and electrical modulus properties of the sample were studied in the temperature range of 25–300℃ and the frequency range of 1 kHz–1 MHz. Typical relaxor behavior observed in the dielectric studies was confirmed by Vogel–Fulcher fitting. From the Nyquist plots, the temperature dependent contribution of grain and grain boundary effect was confirmed. The non-Debye type of relaxation was found using the complex impedance spectroscopy. The magnetic study revealed that the sample had paramagnetic behavior at room temperature. Magneto-electric(ME) coefficient was obtained by changing DC bias magnetic field. This type of lead-free relaxor ferroelectric compound may be useful for high-temperature applications.

Electrical properties of rare earth based tungsten bronze vanadates

Barium based tungsten bronze （TB） oxides having high dielectric constant and low loss, can be effectively used as transducers, actuators, capacitors and also in memory devices. All these characteristics stimulated the researchers to replace toxic and hazardous lead based materials by barium based TB materials from industry. In the present research work, polycrystalline samples of BaaSrRTi3VTO30 （R=Dy, Sm, La） were synthesized by a high temperature solid state reaction technique. Preliminary structural （X-ray diffraction） analyses of these com- pounds showed the formation of single-phase orthorhombic structures at room temperature having average crystallite size of the order of some nanometer for all the compounds. The scanning electron micrographs （SEM） provided information on the quality of the samples and showed more or less homogeneous distribution of grains over the entire surface of the samples. Detailed dielectric study in a wide temperature range （30-500 ℃） showed ferro to para phase transition for Dy and Sm substituted samples whereas no such transition was observed for La substituted samples. Both the grain and grain boundary resistances exhibited negative temperature coefficient of resistance behavior much like semiconductors. The dc conductivity of all the compounds obeyed Arrhenius relation.

Impedance spectroscopy study of Na_(2)SmV_(5)O_(15) ceramics

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.

Complex impedance properties of LiSr_(2)Nb_(5)O_(15) ceramic

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.

Electrical properties of Na_(2)Pb_(2)R_(2)W_(2)Ti_(4)V_(4)O_(30)(R=Dy,Pr)ceramics

The polycrystalline samples of complex tungsten bronze(TB)Na_(2)Pb_(2)R_(2)W_(2)Ti_(4)V_(4)O_(30)(R=Dy,Pr)compounds were prepared by solid-state reaction technique.Room-temperature preliminary structural studies confirm the formation of the compounds in the orthorhombic crystal system.Detailed studies of electrical properties of the materials using complex impedance spectroscopy technique exhibit that the impedance and related parameters are strongly dependent upon temperature and microstructure(bulk,grain boundary,etc).An observation of negative temperature coefficient of resistance(NTCR)suggests the materials have semiconducting properties.The variation of AC conductivity with temperature shows a typical Arrhenius behavior of the materials.Both the samples obey Jonscher’s universal power law.The existence of hopping mechanism in the electrical transport processes in the system with non-exponential type of conductivity relaxation is confirmed by electrical modulus analysis.

Study of multiferroic properties of Bi_(2)Fe_(2)WO_(9) ceramic for devices application

The Bi_(2)Fe_(2)WO_(9) ceramic was prepared using a standard solid-state reaction technique.Preliminary analysis of X-ray diffraction pattern revealed the formation of single-phase compound with orthorhombic crystal symmetry.The surface morphology of the material captured using scanning electron microscope(SEM)exhibits formation of a densely packed microstructure.Comprehensive study of dielectric properties showed two anomalies at 200℃and 450℃:first one may be related to magnetic whereas second one may be related to ferroelectric phase transition.The field dependent magnetic study of the material shows the existence of small remnant magnetization(M_(r))of 0.052 emμ/g at room temperature.The existence of magneto-electric(ME)coupling coefficient along with above properties confirms multi-ferroic characteristics of the compound.Selected range temperature and frequency dependent electrical parameters(impedance,modulus,conductivity)of the compound shows that electric properties are correlated to its microstructure.Detailed studies of frequency dependence of ac conductivity suggest that the material obeys Jonscher's universal power law.

Dielectric and electrical properties of Na_(2)Pb_(2)La_(2)W_(2)Ti_(4)Ta_(4)O_(30) electroceramics

The polycrystalline sample of complex tungsten-bronze type compound(Na_(2)Pb_(2)La_(2)W_(2)Ti_(4)Ta_(4)O_(30))was prepared by a high-temperature solid-state reaction technique.Room temperature preliminary structural study using X-ray diffraction(XRD)data exhibits the formation of a single-phase new compound.The SEM micrograph of the compound exhibits non uniform rectangular grains distributed throughout the sample surface.Detailed studies of dielectric parameters(εr,tanδ)as a function of temperature and frequency,and P-E hysteresis(spontaneous polarization)confirmed the existence of ferroelectricity in the material.Complex impedance spectroscopy analysis,carried out as a function of frequency at different temperatures,established a correlation between the microstructure and electrical properties of the material.The electrical relaxation process occurring in the material is temperature dependent.The activation energy found from the Arrhenius plot that the conduction process in the material is of mixed type.The nature of frequency dependence of ac conductivity suggests that the material obeys Jonscher’s universal power law.

SYNTHESIS AND CHARACTERIZATION OF COMPLEX FERROELECTRIC OXIDE

The polycrystalline sample of Li_(2)Pb_(2)Pr_(2)W_(2)Ti_(4)V_(4)O_(30) was prepared by a solid-state reaction technique.The preparation conditions of the compound have been optimized using thermal analysis(DTA and TGA)technique.Room temperature structural analysis confirms the formation of single phase compound in orthorhombic crystal system.The surface morphology of the sample,recorded by scanning electron microscope,shows uniform grain distribution on the surface of the sample.The observation of hysteresis loop confirmed that the material has ferroelectric properties at room temperature.Electrical properties of the material were studied by complex impedance spectroscopic technique.Temperature dependence of electrical parameters(impedance,modulus,etc.)is strongly correlated to the micro-structural characteristics(bulk,grain boundary,etc.)of the sample.A typical temperature-dependent resistive characteristic of the sample(i.e.,negative temperature coe±cient of resistance(NTCR))exhibits its semiconducting properties.The temperature dependence of dc conductivity shows a typical Arrhenius behavior.A signature of ionic conductivity in the system was observed in ac conductivity spectrum.The sample obeys Jonscher's universal power law.The hopping mechanism for electrical transport properties of the system with nonexponential-type conductivity relaxation was suggested from the electrical modulus analysis.

Colossal dielectric response and complex impedance analysis of LaFeO_(3)ceramics

The present investigations mainly focused on the colossal dielectric response and complex impedance analysis of LaFeO3 ceramics.The studied sample was prepared by a citrate gel method.Structural and microstructural properties are analyzed from the XRD pattern and SEM micrograph.The anomalies in the dielectric constant versus temperature plots are analyzed on the basis of polarization induced by the Maxwell-Wagner mechanisms and ferromagnetic interaction between the Fe3+ions driven by the oxygen vacancy mediated Fe^(3+)-Vo-Fe3+exchange interaction A giant dielectric permittivity in the order of~105 was observed in the sample even at the room temperature for 100 Hz.The colossal dielectric constant in LaFeO3 is mainly driven by the internal barrier layer capacitor(IBLC)formation.The formation of IBLC was explained on the basis of highly insulating grain boundary and less resistive/semiconducting grain,which was confirmed from both the resistance and capacitance of grain and grain boundary from the impedance analysis.The non-Debye-type relaxation process associated with the grain and grain boundary effect was investigated from the broad and asymmetric relaxation peak.The relaxation time for both the grain and grain boundary effect was also calculated.In addition to this,we have also analyzed the normalized bode plot of imaginary part of impedance and electrical modulus which suggests the relaxation process dominated by the short-range movement of charge carriers.

Dielectric response and pyroelectric properties of lead-free ferroelectric Ba_(3)(VO_(4))_(2)

The current paper presents results of dielectric response,pyroelectric behavior and conductivity study of lead-free ferroelectric barium orthovanadate(Ba_(3)(VO_(4))_(2)or Ba_(3)V_(2)O_(8))ceramic,for a wide range of temperature and frequency.An X-ray diffraction study suggests the formation of a single-phase compound in trigonal crystal system.The SEM micrograph of gold-coated pellet sample shows well-defined and homogeneous morphology.Detailed studies of dielectric parameters(ε_(r)and tanδ
)of the compound as a function of temperature and frequency reveal their independence over a wide range of temperature and frequency.The nature of Polarization versus electric field(P-E)hysteresis loop of Ba_(3)V_(2)O_(8)at room temperature suggests its ferroelectric nature.The temperature dependence of pyroelectric coefficient and figure of merits of the sample support its dielectric response.The nature of variation of dc conductivity with temperature confirms the Arrhenius and negative temperature coefficient of resistance(NTCR)behavior of the material.

Studies of electrical conductivity and magnetic properties of Bi_(1-x)Gd_(x)FeO_(3) multiferroics

The polycrystalline samples of Bi_(1-x)Gd_(x)FeO_(3)(x=0,0.1,and 0.2)muliferroic oxides have been synthesized by a solid-state reaction/mixed oxide technique.The preliminary X-ray structural analysis with room temperature diffraction data confirmed the formation of single-phase systems.Study of room temperature scanning electron micrograph(SEM)of the surface of the above samples exhibits a uniform distribution of plate-and rod shaped grains throughout the sample surface with less porosity.The dielectric behavior of the materials was studied in a wide range of frequency(1 kHz-1 MHz)and temperature(30-400℃).The nature of temperature dependence of de conductivity confirms the Arrhenius behavior of the materials.The frequency-temperature dependence of ac conductivity suggests that the material obeys Jonscher's universal power law.An increase in Gd-content results in the enhancement of spontaneous magnetization BiFeO_(3)(BFO)due to the collapse of spin cycloid structure.The magnetoelectric coupling coefficient of BFO has been enhanced on Gd-substitution.

IMPEDANCE SPECTROSCOPY AND MAGNETIC PROPERTIES OF AURIVILLIUS STRUCTURES

Bi_(9-x)Fe_(5+x)Ti_(3)O_(2)7(x=0-3)compounds of bismuth layered perovskite structure have been successfully prepared by solid-state reaction method.X-ray diffraction(XRD)studies revealed the orthorhombic crystal structure of all the compounds.Impedance spectroscopy has been stu-died to characterize the electrical properties of polycrystalline Bi_(9-x)Fe_(5+x)Ti_(3)O_(2)7(x=0-3)compounds.The shape of complex impedance curves inferred the contribution of bulk and grain boundary effects on the electrical properties of the compounds.Temperature dependent magne-tization measurements were made from 2 K to 300 K.Narrow hysteresis loops observed at room temperature indicate antiferromagnetic behavior of the compounds.

STUDIES OF STRUCTURAL AND ELECTRICAL BEHAVIOR OF SAMARIUM BARIUM TUNGSTATE CERAMICS

Polycrystalline samples of samarium barium tungstate[Sm_(2)(Ba_(0.5)W_(0.5)T_(2)O_(7):(SBW)]pyrochlore structure type oxides have been prepared by a solid-state reaction technique.X-ray di®raction(XRD)patterns of this compound at room temperature suggest the formation of a single phase compound with orthorhombic structure.Studies of the dielectric constant and dielectric loss of compound as a function of frequency(4 kHz-1MHz)at room temperature,and as a function of temperature(23-350℃)at 20 and 50 kHz frequencies suggest that the compound does not have dielectric anomaly.The variation of dc resistivity suggests the semiconductor characteristics of the material.The value of activation energy(E_(a)-0.43 at 20 kHz and E_(a)-0.29 at 50 kHz)of the above mentioned compound has been calculated from the slope of the ln-ac versus 1/T graph in the high temperature region(>240℃).The low value of activation energy supports the superionic nature of the compounds in the high temperature region.