Positive Temperature Coefficient Of Resistivity Research Articles

Temperature Dependence of Electrical Properties of ZnO Nanorods Array

Zinc oxide nanostructures (nanotubes, nanorods, nanowhiskers, etc.) are a promising material for various electronics devices for power system and green energy such as piezoelectric energy harvesters and solar cells. Electrical properties of ZnO nanorods grown on a glass substrate by the hydrothermal method in an aqueous solution of zinc nitrate were investigated in this work. The SEM micrograph shows that the grown nanorods are vertically oriented and the XRD pattern confirms its crystallinity with (002) preferred orientation. The temperature dependent resistivity of ZnO nanorods array measured from 300 to 523 K shows variation in resistance from 5·109 Ω to 3·106 W and temperature hysteresis and region with positive temperature coefficient of resistance at the heating that was not observed at cooling. The origin of this behavior is explained with the two competing processes - thermal generation of electrons and oxygen species adsorption on the ZnO surface. Oxygen adsorption leads to decrease in the number of oxygen vacancies that are electron donors, and consequently to a decrease in conductivity of ZnO nanorods. The values of activation energy of conductivity were calculated from the slope of linear regions on the Arrhenius plot which are 0.246, 1.466 and 0.248 eV for the heating curve and 0.650 and 0.315 eV for the cooling curve.

Magnetic field and temperature effect on physical properties of LaFeO3–Pb(Zr0.58Ti0.42)O3 multiferroic nanocomposites

Magnetoelectric composites of xLaFeO3–(1 − x)Pb(Zr0.58Ti0.42)O3 (x = 0.2 and 0.3) have been prepared by pyrophoric reaction process. The observed room temperature magnetoelectric coefficient is enhanced with the increase of LaFeO3 content in nanocomposites. The maximum value of magnetoelectric coupling is found to be ∼1.5 mV/cm-Oe and ∼0.3 mV/cm-Oe, which may be due to the strain mediation of piezomagnetic phase and magnetodielectric property of the material. The frequency dependent AC conductivity at several temperatures indicates the thermally activated conduction process in the system. The electrical conductivity (both AC and DC) shows positive temperature coefficient resistance effect of the system where AC conductivity obeys Jonscher’s power law. It demonstrates the hopping mechanism via small as well as large polaronic conduction process in the system. Maximum change of magnetoimpedance (∼185%) is observed at a frequency of 100 Hz at room temperature. The observed magnetoimpedance effect can be explained considering the skin effect. The magnetocapacitance effect shows the maximum value (∼60%) at lower frequency regime at room temperature attributing the evidence of Maxwell–Wagner interfacial or space charge polarization in the sample. At room temperature the magnetic field dependent capacitance of these samples is corroborating the evidence of magnetoelectric coupling.

Metal-like temperature dependent conductivity in fast Li+ ionic conductor Lithium Lanthanum Titanate

Fast Li+ ionic conductor Lithium Lanthanum Titanate (La0.55Li0.35TiO3) is synthesized by the tartaric acid assisted sol-gel synthesis and powder compacts are sintered. The electrical properties of the obtained ceramics are studied at frequencies up to 10 GHz and at temperatures up to 1280 K. The obtained results allow accurate determination of the specific conductivity of ceramic grains, which are found to reach 30 S/m in the region of high temperatures. A strong deviation from the Arrhenius law is observed with continuously decreasing activation energy of conductivity at temperatures T > 400 K, and a metal-like temperature dependent ionic conductivity (which may be also defined by positive temperature coefficient of resistivity - TCR) is observed at T > 1100 K. The phenomenon of this positive TCR may be related to the alteration of the occupancy of A positions by La3+ in La-enriched and La-depleted planes of crystal lattice of LLTO and to the alteration of the conditions for concerted migration of Li+ ions.

Study on the main factors affecting the breakdown voltage of (Bi0.5Na0.5) TiO3-added (Ba0.659Pb0.341)TiO3 PTCR ceramic materials

The breakdown voltage (Vb) was studied for (Bi0.5Na0.5)TiO3 (BNT)-added positive temperature coefficient of resistance (PTCR) ceramic samples based on (Ba0.659Pb0.341)TiO3, which were prepared by a traditional solid-reaction method and sintered in an air atmosphere. By measuring the electrical properties and microstructures of the materials, the breakdown voltage was found to depend on neither the room-temperature resistivity nor the maximum resistivity, but on the grain size (D) of the samples to some extent. With a decrease in the grain size, the Vb value increases rapidly, especially for samples with fine grains. With the help of Heywang-Jonker theory, the depletion width (LD) was calculated to determine the dominant factor affecting the Vb value using the approximate equation Vb= 600 × LD/D + 100; i.e., the breakdown voltage is approximate directly proportional to the ratio of LD/D. However, the room-temperature resistivity increased slightly with LD/D, and the PTC performance remained at a high level (α > 34%, Rmax/Rmin > 1 × 103). It is more advantageous to increase the breakdown voltage by adjusting LD/D than by reducing grain size alone. The variations in the grain size and the depletion layer width of different samples are mainly due to the generation of VNa′ and VBiʺ′ inside of the lattice. The ratio of LD/D can also be used to explain the variation in room-temperature resistivity.

Renormalization of electron–phonon coupling in the Mott–Ioffe–Regel limit due to point defects in the V1−xTix alloy superconductors

We report here the temperature dependence of electrical resistivity ((T)), heat capacity (C(T)) and thermal conductivity ((T)) of superconducting V1−xTix alloys in the absence and presence of external applied magnetic fields. The (T) changes from positive temperature coefficient of resistivity (TCR) to negative TCR at about x = 0.7 indicating that many of these alloys lie close to the Mott–Ioffe–Regel (MIR) limit. The jump in the C(T) across the superconducting transition temperature () indicates that these alloys are in the intermediate coupling limit. The (T) increases in certain V1−xTix alloys as the temperature decreases below the indicating that the phonons dominate the heat conduction in the superconducting state, whereas we found that the electrons are the major carriers of heat in the normal state. Our analysis suggests that the unusual features of thermal conductivity have origin in (i) the electron mean free path approaching the inter atomic distances (MIR limit) and (ii) the renormalization of the phonon mean free path due to the presence of point defects and the electron–phonon interaction.

Gamma radiation induced fabrication of styrene butadiene rubber/ magnetite nanocomposites for positive temperature coefficient thermistors application

A new positive temperature coefficient resistor (PTCR) thermistor based on styrene butadiene rubber/nanomagnetite (SBR/Fe3O4) nanocomposite was successfully fabricated by conventional roll milling technique.XRD, FT-IR,TEM and EDX techniques were utilized to elucidate the developed of magnetite nanoparticles the analyses revealed a diameter of 9–11 nm.The (SBR/Fe3O4) nanocomposite was examined via the XRD patterns and SEM micro images before and after gamma irradiation. The mechanical properties of the developed nanocomposites: tensile strength, elongation at break and elastic modulus were investigated, whilst the thermal stability was analyzed by TGA. Explicit improvement was been noticed by elevation of the nano load and radiation dose within the cited range. The electrical conductivity examination and the derived thermistor constant, sensitivity and stability of irradiated nanocomposite, 10% Fe3O4 at 100 kGy ensured typical PTCR.

Structural, dielectric and electrical behavior of Bi0.85Tm0.15FeO3 ceramic

The (Bi0.85Tm0.15)FeO3 (BTFO) and BiFeO3 (BFO) ceramic compounds have been prepared by using a standard ceramic technology (i.e., high-temperature solid-state reaction route). The formation of the above compounds was checked by the detailed analysis of X-ray diffraction (XRD) data using standard computer programming software ‘POWD’. All the diffraction peaks of the XRD patterns of the above compounds were indexed through JCPDS files of X'Pert High Score plus. These compounds (BFO and BTFO) were found to crystallize in rhombohedral symmetry with few impurity phases present in the structure. A dielectric peak observed in a temperature range of 250C–350 °C is due to the magnetic phase transition occurring in the materials (BFO and BTFO). The calculated value of tolerance factor reveals the degree of distortion occurring in the ideal perovskite structure. Impedance study indicates the presence of both NTCR (negative temperature coefficient of resistivity) and PTCR (positive temperature coefficient of resistivity) behavior in a different temperature range. The role of grain and grain boundary effects in the electrical properties was discussed with the respective fitting parameters (Rg, Rgb, CPE etc.) of the materials. Activation energy has been calculated at different temperature through Nyquist plot, and also from the slopes of Arrhenius (σac∼1/T) plot. The polarization versus electric field (PE) hysteresis loops of BFO and BTFO gave the evidence of ferroelectric behavior present in the compounds.

(Invited) Smart Separator Integrating Self-Healing, Non-Flammable and Detecting Functions with the Objectives of Making Safer and Durable Battery

Most batteries are composed of two solid, electrochemically active layers called electrodes, separated by a polymer membrane infused with a liquid or gel electrolyte. Improving safety, durability while maintaining performances of batteries are highly desirable for consumer electronics, electrical vehicles and grid energy. Whereas the energy density, power density and cycling life of batteries have been significantly improved in the past two decades, battery safety remains an important and unresolved issue. A high battery specific energy density generally increases the energetic response when the batteries are subjected to abuse. Safety issues have become a major obstacle impeding the large-scale application of high-energy-density batteries. To ensure good performance, batteries generally operate within a limited range of current density, voltage and temperature.1 However, at an abnormal temperature, typically caused by shorting, overcharging or other abuse conditions, a series of exothermic reactions can be initiated and rapidly propagate to further increase the internal cell temperature and pressure, which results in catastrophic battery explosion and fire.2,3 Commercial batteries are equipped with external pressure release vents and positive temperature coefficient (PTC) resistors on their cases to prevent overpressure and overheating. However, temperature and pressure increases inside cells can occur at much higher speeds than can be detected by these external devices.4 Thus, internal safety strategies are more effective in preventing thermal runaway. There have been several efforts to design internal functional components to address battery safety issues, including novel separators, electrolyte additives and positive temperature coefficient-modified current collector. Several novel separator approaches, including bilayer or trilayer separators,5,6 thermoresponsive microspheres7 and ceramic particle coating8, are effective in shutting down batteries or improving their thermal tolerance. But, the process is irreversible and the battery is no longer functional afterwards. On the other hand, electroactive polymer separator coatings for overcharge protection have limited operating voltages.9 Additives (for example, flame retardants,10 redox shuttles11) to electrolytes have been also explored. They are called for improvements with the hope of designing one that include wide operating voltage range and cycling stability. Non-flammable or solid-state electrolytes have been proposed with the aim of avoiding volatile solvents, but the battery performance is generally decreased owing to their low ionic conductivity.12,13 PTC-modified current collectors are a promising approach owing to their simplicity and reversible operation.14 But, their application has been limited by low temperature conductivity and a considerable leakage current. Clearly, in spite of efforts made thus far, battery safety remains an important concern, thus calling for new approaches. In this presentation, we will discuss the different strategies explored in the literature to propose smart separator while keeping good power densities, cycle life and safety. We will also report a strategy based on electrospinning and sol-gel chemistry to design separators exhibiting high performances and low flammable properties, compared to celgard.15 This separator integrates organic/inorganic fibers are organized in a 3-dimensional array, delineating a highly porous network. Because of the chemistry of the fibers, it exhibits high wettability with a large family of solvent, good electrolyte up-take while keeping is initial dimension. Because of the processing flexibility, various functions will be added to the fibers bringing it i) good self-healing capability through quadruple hydrogen bonding, ii) complexing capability and iii) restriction in term of intermediate diffusion through the grafting of quaternary ammonium group.

Electrolyte‐Gating‐Induced Metal‐Like Conduction in Nonstoichiometric Organic Crystalline Semiconductors under Simultaneous Bandwidth Control

Heavily doped semiconductors are well investigated and widely used in inorganic electronics. However, controlled heavy doping of organic crystalline semiconductors is yet to be studied because of the lack of suitable methods. This article reports on doping by electrolyte gating combined with bandwidth control by uniaxial stress using a bilayered nonstoichiometric κ–β″‐type charge‐transfer salt, in which the β″ layer exhibits competition between metallic and charge‐ordered insulating states. A change from insulating‐like to metal‐like conduction with a positive temperature coefficient of resistance is induced by the simultaneous application of a negative gate voltage and compressive stress applied by bending the substrate. The simultaneous heavy doping and bandwidth‐control technique presents a novel approach for investigating nonstoichiometric doping of organic semiconductors for novel electronic functions using metal–insulator transitions and superconductivity of correlated electron systems.

Enhanced electrical properties of BaTiO3-based thermosensitive ceramics for multilayer chip thermistors applications by addition of (Bi0.5Na0.5)TiO3

Abstract BaTiO3-based multilayer chip thermistors with the inner electrodes have been designed to meet the requirements of miniaturization and low resistance. Generally, they were prepared by the reduction-reoxidation method to avoid the oxidization of internal electrodes. Due to their limited efficiencies of oxygen adsorption during the process of reoxidation, positive temperature coefficient of resistivity (PTCR) jump of multilayer chip thermistors were difficult to reach a high value. In this work, we have investigated the influence of (Bi0.5Na0.5)TiO3 (BNT) addition and sintering temperature on microstructure and electrical properties of BaTiO3 based multilayer chip thermistor ceramics. The measurement of grain size and density suggested that a moderate addition of BNT could facilitate grain growth when the ceramic is sintered at a suitable temperature. This phenomenon was attributed to the liquid Na-rich phase at a suitable temperature, and it was affected by the Na+-rich grain shell during the sintering process. Meanwhile, Bi3+ was found to increase the adsorption efficiency of oxygen at the grain boundaries, thus promoted PTCR jump. Multilayer chip thermistors ceramics with high PTCR jump of 3.55 × 103 and low RT resistivity of 18.4 Ω cm were obtained after sintering at 1125 °C with 0.3mol% BNT additive.

Near-zero temperature coefficient of resistance of hybrid resistor fabricated with carbon nanotube and metal alloy

A hybrid resistor has been fabricated by parallely connecting carbon nanotube (CNT) fiber with negative temperature coefficient of resistance (TCR) and metal alloy with positive TCR to achieve near zero TCR. The CNT fibers were prepared by yarning CNTs grown on the silicone substrate by chemical vapor deposition (CVD) method. The CNT fiber resistors were fabricated by winding CNT fiber on the ceramic rod. Metal terminals were connected at both ends of the CNT fiber wound on the ceramic rod. The metal alloy resistors were fabricated with copper (Cu) and nickel (Ni) with different weight compositions. Electrical resistance and thermal stability (in terms of TCR in this work) of the CNT fiber resistors, the metal alloy resistors, and the hybrid resistors were measured as 7.94 Ω and −870 ppm/°C, 7.94 Ω and 1100 ppm/°C, and 3.97 Ω and −2 ppm/°C, respectively. In case of parallelly connected resistors with suitable combination, the resistance was lower than that of resistor with lower value, and the TCR approached to near zero. Finally, we propose a theoretical approach for adjusting resistance and TCR of the hybrid resistor composed of metal alloy and CNT fibers.

Transport Evidence for Sulfur Vacancies as the Origin of Unintentional n-Type Doping in Pyrite FeS2.

Pyrite FeS2 has long been considered a potential earth-abundant low-cost photovoltaic material for thin-film solar cells but has been plagued by low power conversion efficiencies and open-circuit voltages. Recent efforts have identified a lack of understanding and control of doping, as well as uncontrolled surface conduction, as key roadblocks to the development of pyrite photovoltaics. In particular, while n-type bulk behavior in unintentionally doped single crystals and thin films is speculated to arise from sulfur vacancies (VS), proof remains elusive. Here, we provide strong evidence, from extensive electronic transport measurements on high-quality crystals, that VS are deep donors in bulk pyrite. Otherwise identical crystals grown via chemical vapor transport under varied S vapor pressures are thoroughly characterized structurally and chemically, and shown to exhibit systematically different electronic transport. Decreased S vapor pressure during growth leads to reduced bulk resistivity, increased bulk Hall electron density, reduced transport activation energy, onset of positive temperature coefficient of resistivity, and approach to an insulator-metal transition, all as would be expected from increased VS donor density. Impurity analyses show that these trends are uncorrelated with metal impurity concentration and that extracted donor densities significantly exceedtotal impurity concentrations, directly evidencing a native defect. Well-controlled, wide-range n-doping of pyrite is thus achieved via the control of VS concentration, with substantial implications for photovoltaic and other applications. The location of the VS state within the gap, the influence of specific impurities,unusual aspects to the insulator-metal transition, and the influence of doping on surface conduction are also discussed.

Study of La-doped barium titanate ceramics obtained by laser sintering technique

This work studies the influence of laser sintering on the semiconducting properties of La-doped BaTiO3 (BTL) ceramics. The BTL powders were synthesized using a solid-state reaction method and sintered via a new laser sintering technique. In this technique, a CO2 laser is used as the main heating source and no atmosphere control was employed. The BTL laser-sintered ceramics exhibited high relative density and a crack-free homogeneous microstructures after sintering at a laser power density of 5.0 W/mm2 for 30 s. The samples exhibited a positive temperature coefficient of resistivity (PTCR) increase of two orders of magnitude, and a room-temperature resistivity of 105 Ω.cm, even when sintered in an open atmosphere. X-ray diffraction, scanning electron microscopy, differential scanning calorimetry, and UV-Vis and impedance spectroscopy techniques were employed and results provided.

Ethylene-octene copolymer and carbon black composite electro-thermal properties for self-regulating heating

Carbon black - ethylene-octene copolymer (EOC-CB) composite electro-thermal properties were investigated for using the composite as self-regulating heating material. The materials electrical resistance change with temperature change was investigated. Additionally, while a voltage of 30 V was applied, the sample temperature and electrical current strength was measured. The samples with 15 to 20 phr CB showed positive temperature coefficient of resistivity and could be used as self-regulating heating materials. For different concentrations of CB the achieved equilibrium temperatures were between 30°C to 60°C (with 30 V) and could be used to comfortably warm the human body.

Additive manufacturing of barium titanate based ceramic heaters with positive temperature coefficient of resistance (PTCR)

Lanthanum/manganese doped barium titanate (BT) based PTCR functional heater elements/structures were fabricated with desirable electrical properties for the first time using Additive Manufacturing (AM). 3D printed components of varying size and shape and prototype honeycomb lattices with high density were achieved through AM. Aqueous, less organic containing (2.5 wt% additives versus 10–30 wt% added typically), eco-friendly ink formulations were developed with suitable rheological properties for 3D printing. For BT prints, the sintered densities of the 3D ceramic parts were found to be >99% TD, highest reported value so far. The microstructure, electrical properties and heating characteristics of the printed PTCR components were studied in detail and their thermal stability evaluated using infrared imaging and benchmarked against commercial PTCR heating element. The heating behaviour of the solid and porous 3D printed components was demonstrated to be similar, paving the way for light weight (˜47% reduction in weight) heaters suitable for automotive/aerospace applications and less materials wastage during device fabrication.

Study on positive temperature coefficient of resistivity of co-doped BaTiO3 with Curie temperature in room temperature region

As a temperature self-regulating heater material, the doped BaTiO3 exhibits an attractive application perspective in the thermal management of electrical devices. However, the high Curie temperature does not meet the requirement in the thermal control application. In this work, (Ba0.997−xCe0.003Srx)(TiNb0.002)O3 (x=0.2, 0.3, 0.35, abbreviated as BCSTNs) ceramics were prepared by the solid-state reaction method. The purpose of doping different content of strontium is to shift the Curie temperature of BaTiO3-based ceramic to the ambient temperature region, maintaining excellent PTC effect and low room-temperature resistivity by codoped cation ions in Ba- and Ti-site. The influences of sintering temperature and soak time on the microstructure as well as electrical properties of BCSTNs ceramics have been studied. The X-ray diffraction reveals that the composition with x=0.35 exhibits the coexistence of tetragonal and cubic lattice symmetries, confirmed by the Rietveld structure refinement. The dense microstructure with average grain sizes 0.84–7.87 μm was observed for BCSTN ceramics. Temperature-resistivity measurements demonstrate that TC of the ceramics with x=0.35 shifted to the room temperature region. Additionally, the BCSTN ceramic with heavy doping Sr exhibits relative low room-temperature resistivity and the resistance jump greater than 2.0 orders of magnitude.

Electric and magnetic transport analysis of Na0.5Bi0.5TiO3 nanoparticles for temperature and magnetoimpedance sensor applications

Abstract Polycrystalline nano grain size Na0.5Bi0.5TiO3 (NBT) system is synthesized by using modified sol–gel method. X-ray diffraction (XRD), Transmission electron microscopy (TEM) studies and Field emission scanning electron microscopy (FESEM) are employed for structural and morphological confirmation. Electrochemical transport properties of this nano system have been investigated systematically in the range of temperature (30 °C−450 °C) and frequency (100 Hz−1 MHz) with the help of complex impedance spectroscopic technique. From impedance and modulus results, two (one at low and another at high temperature regime) positive temperature coefficient of resistance (PTCR) to negative temperature coefficient of resistance (NTCR) transitions are observed which is useful for electrochemical temperature sensor application. From electric transport analysis it found that due to small polaron hopping of charge carriers at NBT-NBT interfaces system shown PTCR nature. However, the system has shown both −ve magnetoresistance [MR (%)] and magnetocapacitance [MC (%)] at RT due to overlapping of large polaron tunnelling (OLPT) at NBT-NBT interfaces (which is explored with the help of magnetic transport analysis).

Continuous transition from weakly localized regime to strong localization regime in Nd0.7La0.3NiO3 films

We report an investigation of metal-insulator transition (MIT) using conductivity and magnetoconductance (MC) measurements down to 0.3 K in Nd0.7La0.3NiO3 films grown on crystalline substrates of LaAlO3 (LAO), SrTiO3 (STO), and NdGaO3 (NGO) by pulsed laser deposition. The film grown on LAO experiences a compressive strain and shows metallic behavior with the onset of a weak resistivity upturn below 2 K which is linked to the onset of weak localization contribution. Films grown on STO and NGO show a cross-over from a positive temperature coefficient (PTC) resistance regime to negative temperature coefficient (NTC) resistance regime at definite temperatures. We establish that a cross-over from PTC to NTC on cooling does not necessarily constitute a MIT because the extrapolated conductivity at zero temperature though small (<10 S cm−1) is finite, signaling the existence of a bad metallic state and absence of an activated transport. The value of for films grown on NGO is reduced by a factor of 40 compared to that for films grown on STO. We show that a combination of certain physical factors makes substituted nickelate (that are known to exhibit first-order Mott type transition), undergo a continuous transition as seen in systems undergoing disorder/composition driven Anderson transition. The MC measurement also supports the above observation and shows that at low temperatures, there exists a positive MC that arises from the quantum interference which co-exists with a spin-related negative MC that becomes progressively stronger as the electrons approach a strongly localized state in the film grown on NGO.

Thermoresistance of p‐Type 4H–SiC Integrated MEMS Devices for High‐Temperature Sensing

There is an increasing demand for the development and integration of multifunctional sensing modules into power electronic devices that can operate in high temperature environments. Here, the authors demonstrate the tunable thermoresistance of p‐type 4H–SiC for a wide temperature range from the room temperature to above 800 K with integrated flow sensing functionality into a single power electronic chip. The electrical resistance of p‐type 4H–SiC is found to exponentially decrease with increasing temperature to a threshold temperature of 536 K. The temperature coefficient of resistance (TCR) shows a large and negative value from −2100 to −7600 ppm K−1, corresponding to a thermal index of 625 K. From the threshold temperature of 536–846 K, the electrical resistance shows excellent linearity with a positive TCR value of 900 ppm K−1. The authors successfully demonstrate the integration of p–4H–SiC flow sensing functionality with a high sensitivity of 1.035 μA(m s−1)−0.5 mW−1. These insights in the electrical transport of p–4H–SiC aid to improve the performance of p–4H–SiC integrated temperature and flow sensing systems, as well as the design consideration and integration of thermal sensors into 4H–SiC power electronic systems operating at high temperatures of up to 846 K.

Influence of Sintering Time on the PTCR Effect of Nb2O5-doped BaTiO3 Ceramics

The effects of the sintering time on the electrical properties and the positive temperature coefficient of resistance (PTCR) effect of Ba1.006(Ti1-xNbx)O3 (BTN) ceramics were investigated, which were sintered at 1190 oC for 0.5-6 hours in a reducing atmosphere and then re-oxidized at 800 oC for 1 hour. The results indicated that the sintering time affected the electrical properties and the PTCR effect of the multilayer BTN samples, whose room-temperature resistance decreased with an increase of the sintering time at same sintering temperature of 1190 oC. However, the resistance jump first increased and then reduced as a function of the sintering time. Furthermore, The BTN ceramics exhibited a pronounced PTCR effect, with a resistance jump greater by 3.6 orders of magnitude, along with a low RT resistance of 0.14 Ω at a reoxidated temperature of 800 oC after sintering at 1190 oC for 2 h in a reducing atmosphere. In addition, the activation energy of samples obtained at different sintering times had also been investigated.