Temperature Coefficient Of Resistance Behavior Research Articles

Structural and impedance spectroscopy study of Samarium modified Barium Zirconium Titanate ceramic prepared by mechanochemical route

Samarium modified Barium Zirconium Titanate (BZT) ceramics with general formula [Ba1−xSm2x/3](Zr0.05Ti0.95O3) [x = 0, 0.01, 0.02, 0.03 and 0.04] have been prepared by high energy ball milling. The Rietveld refinement of BaZr0.05Ti0.95O3 (BZT) shows a single phase tetragonal symmetry with space group P4mmm and TEM micrograph shows that the crystalline size is in the submicron range. X-ray diffraction (XRD) patterns confirm that no phase change occurs with the addition of Samarium in BZT upto x ≤ 0.03 and a small pyrochlore phase exists at x = 0.04. The complex impedance (Nyquist) plots display a single semicircle highlighting the influence of grain resistance on the electrical behavior. Negative temperature coefficient of resistance behavior is observed in all compositions. The activation energy calculated from Z″ and DC conductivity confirms that the oxygen vacancies play an important role in the conduction mechanism.

Structural, dielectric and optical properties of sol–gel synthesized 0.55Ba(Zr0.2Ti0.8)O3–0.45(Ba0.7Ca0.3)TiO3 ceramic

Lead-free polycrystalline ceramic 0.55Ba(Zr0.2Ti0.8)O3–0.45(Ba0.7Ca0.3)TiO3 (0.55BZT–0.45BCT) was synthesized by sol–gel method and the dielectric, impedance and optical properties of this ceramic were studied. X-ray diffraction analysis revealed the formation of pure perovskite phase with the coexistence of tetragonal and rhombohedral structures. The high value of dielectric constant (~6,985) with low dielectric loss (~0.013) was obtained at room temperature. Bulk and grain boundary resistances were measured by impedance analysis, which revealed negative temperature coefficient of resistance behaviour in this ceramic. The estimated value of optical band gap was found to be ~3.16 eV, which is related to the presence of intermediate energy levels. Two emission bands one at ~365 nm (UV region) and another at ~465 nm (blue region) were observed in photoluminescence spectrum at room temperature.

A Comparative Study Of Electrical Properties Of Some Rare Earth Based Tungsten Bronze Ceramics

The advent of nanoscience & technology have completely changed the orientation/direction of studies of eco-friendly (lead-free) materials bringing them at the forefront of scientific developments with considerably enhanced physical properties suitable for a wide variety of challenging applications. Barium based ferroelectric materials have gained much importance due to their vast applications as they possess high dielectric constant, non-linear spontaneous polarization, negative temperature coefficient of resistance behavior etc.. All these characteristics stimulated the researchers to replace toxic and hazardous lead based materials by barium based TB materials from industry. Our present research work deals with the synthesis of polycrystalline samples of Ba2Sr3RTi3V7O30 (R = Gd, Sm) by a high temperature solid state reaction technique and a comparative study of the electrical properties of the samples. Preliminary structural (XRD) analyses of these compounds show the formation of single-phase orthorhombic structures at room temperature having average crystallite size of the order of some nanometer for both the compounds. The electrical properties for both the samples are studied in a wide range of temperature (30–500 o C) and frequency (100Hz-1MHz). The dielectric properties suggest that both the compounds have undergone ferroelectric-paraelectric phase transition well above the room temperatures (i.e., 230 and 313 0 C for R= Sm and Gd respectively at frequency 100 kHz).The bulk resistance of the materials exhibits negative temperature coefficient of resistance behavior as observed in semiconductors.

Structural, Electrical, and Optical Behavior of Strontium Bismuth Titanate Ceramic

In this report, we present the structural, electrical, and optical study of layer-structured SrBi4Ti4O15 (SBT) ceramic prepared by solid-state reaction route. The X-ray diffraction and Rietveld refinement studies show a single-phase orthorhombic structure with space group A21am. The scanning electron micrograph shows plate-like grains. The various Raman peaks originated due to the TiO6 octahedron confirm the orthorhombic structure. The temperature-dependent dielectric study shows a normal ferroelectric phase transition with a transition temperature at 813 K (540 °C). Impedance studies show a non-Debye-type relaxation and relaxation frequency shift to higher side with increase in temperature. The Nyquist plot shows overlapping semicircles which results the existence of both for grain and grain boundary effect in SBT ceramic. The frequency-dependent AC conductivity at different temperatures indicates that the conduction process is thermally activated and the spectra follow the universal power law. The variation of DC conductivity confirms that the SBT ceramic exhibits negative temperature coefficient of resistance behavior. The Ferroelectric behavior is studied by hysteresis loop. The optical band gap is found to be 2.93 eV from the UV–Visible spectroscopy study. The room-temperature photoluminescence study shows a strong red emission.

Effect of Praseodymium on Electrical Properties of BiFeO3 Multiferroic

Polycrystalline samples of Bi1−xPrxFeO3 (BPFO) (x = 0, 0.05, 0.1, 0.15) were synthesized by a solid-state reaction technique. Preliminary x-ray structural analysis confirmed the formation of a single-phase compound of BPFO. Scanning electron micrographs recorded at room temperature on pellet samples showed: (i) a uniform distribution of grains on the surface of the samples (with fewer voids) and (ii) reduction of grain size with increasing Pr content of the BPFO samples. Detailed studies of the impedance and electrical modulus of the materials, carried out in a wide range of frequency (1 kHz to 1 MHz) at different temperatures (25°C to 400°C), have provided many interesting results including a significant decrease in loss tangent, structural stability, etc. The variation of the alternating-current (ac) and direct-current (dc) conductivity with inverse absolute temperature follows an Arrhenius relation. The decrease in leakage current and the negative temperature coefficient of resistance behavior with increasing Pr content of BPFO are important observations of this work.

Dielectric, magnetic and electrical properties of ZnFe2O4 ceramics

The polycrystalline sample of ZnFe2O4 was prepared by a high-temperature solid-state reaction technique. Preliminary X-ray diffraction studies of the compound showed the formation of a single-phase compound at room temperature. Studies of dielectric properties (er, tan δ) of the above compound as a function of frequency in a wide temperature range show dielectric anomalies signifying existence of possible ferroelectric to paraelectric phase transition in the material. The confirmation of this assumption was made with observation of ferroelectric hysteresis loop at room temperature. Magnetic measurement exhibits anti-ferromagnetic nature of the sample. Studies of the zero-field cooled and the field-cooled magnetization in dc field provided the blocking temperature TB. The temperature dependence of electrical parameters (impedance, modulus, conductivity, etc.) of the material exhibits a strong correlation between the microstructure (i.e., bulk, grain boundary, etc.) and electrical parameters of the material. Detailed studies of impedance parameters have provided an insight into the electrical properties and understanding of types of relaxation process in the material. The temperature variation of dc resistivity/conductivity exhibits negative temperature coefficient of resistance behaviour of the material. The frequency dependence of ac conductivity suggests that the material obeys Jonscher’s universal power law.

Frequency and temperature dependence dielectric behavior of barium zirconate titanate nanocrystalline powder obtained by mechanochemical synthesis

Nanocrystalline barium zirconium titanate ceramic has been synthesized by high-energy ball milling. This nano-ceramic is characterized by X-ray diffraction, scanning electron microscopy, dielectric study and impedance spectroscopy. The X-ray diffraction pattern shows single phase ceramic of tertragonal symmetry with space group P4 mm. Temperature and frequency dependent dielectric study of the sample shows a normal ferroelectric phase transition behavior. Impedance spectroscopy analyses reveal a non-Debye type relaxation phenomenon. A significant shift in impedance loss peaks toward higher frequency side indicates conduction in material and favoring the long range motion of mobile charge carriers. Grain and grain boundary conduction is observed from complex impedance spectrum by the appearance of two semicircular arcs in the Nyquist plot. The frequency dependent ac conductivity at different temperatures indicates that the conduction process is thermally activated. The variation of dc conductivity exhibited a negative temperature coefficient of resistance behavior.

Dielectric and Pyroelectric Properties of La- and Pr-Modified Tungsten-Bronze Ferroelectrics

The polycrystalline materials Li2Pb2R2W2Ti4Nb4O30 (R = La, Pr) of the tungsten-bronze structural family have been synthesized using a high- temperature mixed-oxide method. Room-temperature x-ray diffraction (XRD) analysis confirms the formation of single-phase compounds. Room-temperature scanning electron micrography of the pellet samples shows a uniform distribution of well-defined different sizes of grains on the surface of the samples, confirming the formation of single-phase compounds. Study of the frequency and temperature dependence of the dielectric constant and loss tangent suggests the existence of dielectric dispersion in the materials. The ferroelectric phase transition in the samples has been studied based on the variation of fitting parameters (calculated from a theoretical model) with temperature. Studies of pyroelectric properties [figure of merit (FOM) and coefficient] show that the materials have reasonably high FOM useful for pyroelectric detectors. The variation of alternating-current (AC) and direct-current (DC) conductivity with inverse absolute temperature (obtained from dielectric data) follows a typical Arrhenius relation. The low leakage current and negative temperature coefficient of resistance behavior of the samples have been verified from J–E plots.

Synthesis, structure and electrical studies of praseodymium doped barium zirconium titanate

Praseodymium (Pr) doped barium zirconium titanate with nominal composition (Ba1−xPrx)(Zr0.52Ti0.48)O3 (x = 0.1 and 0.2) were synthesized using solid state reaction method. X-ray analysis conform the formation of cubic phase Pr-doped barium zirconium titanate along with minor pyrochloric phase. The increase in grain size after primary investigation reveals the influence of Pr ions on the domain structure and its microstructure. In order to correlate the effect of the chemical composition with the conduction mechanism, different AC electrical parameters have been addressed. The frequency dependant tangent loss of the sample was less for both the ceramics. The temperature dependence results show that the dielectric parameters and resistivity increases as Pr-content in the ceramic increases; this is attributed to the grain size and dipole dynamics. Complex impedance (Z*) plots show frequency dependent behavior as the response for the grain resistance mechanisms. This mechanism has been represented by an equivalent circuit. The temperature dependence of the electrical conductivity and Seebeck coefficient showed n-type non-degenerated semiconductor in the measured temperature range. The temperature dependent conductivity measurement suggests a novel negative temperature coefficient of resistance behavior of the samples. Furthermore, the frequency dependent conductivity plot shows increasing behavior.

Electrical Conduction in (Na0.5Bi0.5)1−xBaxTiO3 (0≤x≤1) Ceramic by Complex Impedance/Modulus Spectroscopy

The present work describes the piezoelectric, impedance, and conductivity studies of (Na0.5Bi0.5)1−xBaxTiO3; (1-x)BNT-xBT (0≤x≤1) ceramics. The ceramics were prepared by conventional ceramic fabrication technique. X-ray diffraction data confirmed the formation of a pure compound in all the compositions. Williamson-Hall plot yielded the apparent crystallite sizes ~26–52 nm, and SEM micrograph showed grain sizes ranging between 1.8–3.5 μm for the material samples. Values of longitudinal piezoelectric charge coefficients of the samples poled under a dc electric field of about 2.5 kV/mm at 80°C/15 min indicated that their piezoelectric properties near the MPB are rather sensitive to the phase composition and reach preferred values at x=0.08, where the relative content of the tetragonal phase is significantly higher than that of the monoclinic phase. Complex impedance/modulus spectroscopic analyses indicated the presence of grain-boundary effect along with the bulk contribution and also confirmed the presence of non-Debye type of multiple relaxations in the materials. The temperature dependent electrical conductivity data suggest the negative temperature coefficient of resistance behaviour. The activation energy studies allow insight into the nature of the conduction mechanisms occurring in the materials system which are explained on the basis of hopping model of charge carriers.

High-temperature phase transitions in a quaternary lead based perovskite structured materials with negative temperature coefficient of resistance (NTCR) behavior

Impedance spectroscopy measurements were carried out on lead based, 0.25 (PbZr0.52Ti0.48O3) + 0.25 (PbFe0.50Ta0.50O3) + 0.25 (PbFe0.67W0.33O3) + 0.25 (PbFe0.50Nb0.50O3) (PZT–PFT–PFW–PFN) solid solution over a wide range of temperatures (400–650 K) and frequencies (100 Hz–1 MHz). Impedance data showed the presence of both grains and grain boundaries effects in the electrical transport properties of quaternary. The role of the grains and grain boundaries to the impedance become more prominent around the phase transition (~420 K). Two thermally activated processes were found from the temperature dependences of the relaxation time (τ). Activation energies calculated from relaxation times obtained from imaginary part of impedance were estimated ~1.21 and ~1.84 eV over 400–490 K and 490–650 K respectively. The sum of the activation energies for the grain and grain boundary resistances is basically of the same order of magnitude that is from the impedance at high temperatures. A constant phase element is used in the equivalent electrical circuits for fitting of experimental impedance data. The nature of variation of the grain and grain boundary resistance with temperature suggested negative temperature coefficient of resistance behavior.

Structural, dielectric and electrical properties of lithium silicate ceramics: a comparative study

Lithium silicate (LS) ceramics were prepared via a solid-state reaction technique. Two ceramics with different molar ratios of Li2CO3/SiO2 (1:1 and 1:2) were prepared for dielectric studies. X-ray diffraction pattern showed that Li2CO3/SiO2 (1:1) ceramic is obtained as single phase composition whereas Li2CO3/SiO2 (1:2) ceramic exhibit a multiphase structure with Li2SiO3 as a major phase. Microstructural analysis shows that the compounds have well defined grains separated by grain boundaries. Dielectric and electrical properties of the samples were studied in a wide temperature (30–400 °C) and frequency ranges (100 Hz–5 MHz). From the dielectric studies, we can prescribe Li2CO3/SiO2 (1:2) ceramic as a good dielectric material since it possesses low dielectric loss. Detailed analysis of the impedance data suggests that the conduction of Li2CO3/SiO2 (1:2) ceramic is mainly due to the bulk effects whereas the complex impedance plots of Li2CO3/SiO2 (1:1) ceramic suggests the presence of both bulk as well as grain boundary contributions. The bulk resistance of the samples has been observed to decrease with rise in temperature showing a typical negative temperature coefficient of resistance behavior. The low activation energies of the samples suggest the presence of singly ionized oxygen vacancies in the conduction process.

Temperature dependence of the electrical resistivity and electronic structure of amorphous Fe100−xZrx films and multilayers

The electrical resistivity of amorphous Fe100−xZrx metal alloy films and multilayers has been investigated in a wide temperature and composition range. The overall behavior of the resistivity is consistent with bulk measurements, exhibiting prominent semiconductor-like changes at low temperatures. The transition from positive (metallic) to negative temperature coefficient of resistivity behavior is accompanied by minute changes in magnetoresistance and we can therefore rule out magnetic phase changes as being the cause for the observed changes in the resistivity. Using x-ray absorption and emission spectroscopies we are able to probe the unoccupied and occupied electronic densities of states. The corresponding spectra are found to significantly overlap, as expected for a metallic-like electronic structure and the absence of a band gap. Besides a broadening of the x-ray emission lines expected from an amorphous material, remarkably small differences are observed in the electronic structures when changing the amount of Zr. The resistivity data were modeled and agreement with the Mott variable range hopping model was found, indicating localized electronic states due the disordered structure of the Fe100−xZrx alloys.

Synthesis and electrical properties of (BaTiO3)1 −x (K0.5Bi0.5TiO3) x solid solutions

(BaTiO3)1 − x(K0.5Bi0.5TiO3)x solid solutions exhibiting positive temperature coefficient of resistance behavior have been prepared using BaTiO3 presynthesized through oxalate coprecipitation. The peak in their dielectric permittivity has been shown to shift to higher temperatures (above 120°C) with increasing x. We have examined the effect of K0.5Bi0.5TiO3 content on the microstructure of the (BaTiO3)1 − x(K0.5Bi0.5TiO3)x solid solutions. The results demonstrate that, with increasing x, both the minimum and maximum resistivities of the materials in the temperature range of their positive temperature coefficient of resistance behavior increase. The materials prepared using barium titanate presynthesized by the oxalate route have higher Curie temperatures and temperatures where they exhibit positive temperature coefficient of resistance behavior and lower minimum resistivities than do the materials prepared by solid-state reactions.

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 Ba4SrRTi3V7O30 (R=Dy, Sm, La) were synthesized by a high temperature solid state reaction technique. Preliminary structural (X-ray diffraction) analyses of these compounds 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 °C) 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.

Dielectric and Conductivity Study of SrBi<sub>2</sub>Ta<sub>2</sub>O<sub>9</sub> Ceramic by Microwave Sintering Technique

Bismuth layered structure SrBi2Ta2O9ceramic is prepared by the microwave sintering technique via solid state route at 1100°C. X-ray diffraction analysis is used to analyze the phase purity and identifies the orthorhombic phase with A21am space group. The fracture surface morphology of the sintered pellet is visualized by scanning electron microscopy. Diffusive phase transition behavior is existed in the temperature dependence dielectric study at Tc= 305°C. The electrical ac and dc conductivity study shows the negative temperature coefficient of resistance behavior. Activation energy from the Arrhenius plot is studied to discuss the fatigue property.

Complex impedance and modulus studies of cerium doped barium zirconium titanate solid solution

Nanocrystalline powders of (Ba1−xCex)(Zr0.52Ti0.48)O3 [x=0.1 and 0.2] have been synthesized by conventional solid state reaction method. X-ray diffraction patterns confirm the formation of single phase cubic crystal symmetry. The increase in grain size reveals the influence of Ce ions on microstructure. The electrical behavior of sintered pellets investigated by impedance spectra showed frequency dependent behavior. The complex impedance plots display a single semicircle highlighting the influence of grain resistance on the electrical behavior. The modulus curve illustrates the possibility of non-exponential type conductivity. The values of activation energy calculated from both plots of Z″ and M″ confirms that the oxygen vacancies play an important role in the conduction. The temperature dependant dc-resistivity depicts a negative temperature coefficient of resistance behavior of synthesized ceramics. The ac conductivity of both ceramics increases as a function of frequency due to relaxation phenomenon arisen due to mobile charge carriers.

Dielectric and pyroelectric properties of niobium based complex tungsten bronze ferroelectrics

This paper highlights the dielectric and pyroelectric properties of two new complex tungsten bonze ceramics (K2Pb2Eu2W2Ti4Nb4O30 and K2Pb2Nd2W2Ti4Nb4O30) which were prepared by a high temperature mixed oxide method. Room temperature X-ray structural analysis confirms the formation of single phase compounds. The SEM micrographs show uniform distribution of densely packed rod like grains. Variation of dielectric parameters with temperature (27–500 °C) and frequency (1–5 MHz) shows the phase transition at 315 and 299 °C for the above mentioned respective samples. The temperature dependence of hysteresis loops confirms the existence of ferroelectricity in the materials below transition temperature. The current variation with voltage at different temperatures shows the semiconducting behaviour of the materials. The nature of temperature dependent dc conductivity follows the Arrhenius equation, and reveals the negative temperature coefficient of resistance behaviour of the materials. The current (for a fixed voltage) variation with temperature shows that the materials have high pyroelectric co-efficient and figure of merit, thus making them useful for pyroelectric sensors.

Structure, spectroscopic and piezoelectric properties of BNBT nanocrystalline ceramics

Lead-free nano crystalline (Na0.5Bi0.5)1−xBaxTiO3 (BNBT) ceramics with (x = 0.026, 0.055 and 0.065) have been prepared by solid state sintering technique. In BNBT-6.5 resulted in a splitting of the (2 0 0) peak into two peaks of (0 0 2) and (2 0 0) reflections. Splitting in the peak position reveals the composition is well in morphotropic phase boundary region. Average particle sizes have been calculated and found to be in nanometer range. In the energy dispersive X-ray analysis spectrum elements present in the prepared compositions are Na, Bi, Ba, Ti and O only. Impedance (real Z′) plots provide an indication of increasing conduction with temperature and frequency i.e., negative temperature coefficient of resistance behaviour like semiconductor. The activation energy, Eτ is found to be 0.56, 0.88 and 0.55 eV for BNBT-2.6, BNBT-5.5 and BNBT-6.5 respectively; this suggests strongly that the electrical behaviour of rhombohedral structure in studied materials. BNBT-6.5 ceramics have good properties with piezoelectric constant d33 = 211 pC/N and electromechanical coupling factors kp = 28 % and kt = 25 %. These high d33 BNBT materials can be used for transducer applications. The observed dispersion of the imaginary dielectric constant (e″) is stronger than that of real dielectric constant (e′).

Effect of reoxidation on positive temperature coefficient of resistance behavior for BaTiO3-K0.5Bi0.5TiO3 ceramics

As a positive temperature coefficient of resistivity (PTCR) material, (1-x)BaTiO3-xK0.5Bi0.5TiO3 (BT-KBT, 0.05≦ x ≦0.15) ceramics without any donor doping were prepared by a conventional oxide mixing method. All samples were sintered in an Ar atmosphere at 1280 ~ 1350°C, subsequently, reoxidized at 800 ~ 1100°C in a gas mixture (99 %Ar–1 %O2). The PTCR behavior of BT-KBT ceramics were investigated in terms of KBT content, reoxidation temperature and time. The results showed that the BT-KBT ceramics exhibited an abrupt increase in their resistivity near the Curie temperature (Tc) after annealing in gas mixture, Tc of 0.9BT-0.1KBT ceramic was shifted to a higher temperature (~150°C). Furthermore, the room-temperature resistivity (ρRT) of ceramic samples sintered in Ar and reoxidized in a gas mixture decreased to 102 Ω·cm. The jump in resistivity (maximum resistivity [ρmax]/minimum resistivity [ρmin]) was enhanced by three orders of magnitude through a suitable reduction–reoxidation method without sacrificing the ρRT.