Synthesis of cathode material LiNi<Subscript>1-<Emphasis Type="Italic">y</Emphasis></Subscript>Co<Subscript><Emphasis Type="Italic">y</Emphasis></Subscript>O<Subscript>2</Subscript> by a simplified combustion method

The optimum conditions for synthesizing LiNi_1-y Co _y O₂ (y=0.1, 0.3 and 0.5) by a simplified combustion method, in which the preheating step is omitted, and the electrochemical properties of these materials were investigated. The optimum condition for synthesizing LiNi_0.9Co_0.1O₂ by the simplified combustion method is calcination at 800 °C for 12 h in air in 3.6 mole ratio of urea to nitrate. The LiNi_0.9Co_0.1O₂ synthesized under these conditions shows the smallest R-factor{(I ₀₀₆+I ₁₀₂)/I ₁₀₁} and the largest I ₀₀₃/I ₁₀₄, indicating better hexagonal ordering and less cation mixing, respectively. The LiNi_0.7Co_0.3O₂ synthesized at 800 °C for 12 h in air in 3.6 mole ratio of urea to nitrate has the largest first discharge capacity 156.2 mA h g⁻¹ at 0.5C and shows relatively good cycling performance. This sample shows better hexagonal ordering and less cation mixing than the other samples. The particle size of the LiNi_0.7Co_0.3O₂ is relatively small and its particles are spherical with uniform particle size.     

Structure and electrochemical characterization of LiNi<Subscript>0.3</Subscript>Co<Subscript>0.3</Subscript>Mn<Subscript>0.3</Subscript>Fe<Subscript>0.1</Subscript>O<Subscript>2</Subscript> cathode for lithium secondary battery

A lithium insertion material having the composition LiNi_0.3Co_0.3Mn_0.3Fe_0.1O₂ was synthesized by simple sol-gel method. The structural and electrochemical properties of the sample were investigated using X-ray diffraction spectroscopy (XRD) and the galvanostatic charge-discharge method. Rietvelt analysis of the XRD patterns shows that this compound can be classified as α-NaFeO₂ structure type (R3m; a=2.8689(5) Å and 14.296(5) Å in hexagonal setting). Rietvelt fitting shows that a relatively large amount of Fe and Ni ion occupy the Li layer (3a site) and a relatively large amount of Li occupies the transition metal layer (3b site). LiNi_0.3Co_0.3Mn_0.3Fe_0.1O₂ when cycled in the voltage range 4.3–2.8 V gives an initial discharge capacity of 120 mAh/g, and stable cycling performance. LiNi_0.3Co_0.3Mn_0.3Fe_0.1O₂ in the voltage range 2.8–4.5 V has a discharge capacity of 140 mAh/g, and exhibits a significant loss in capacity during cycling. Ex-situ XRD measurements were performed to study the structure changes of the samples after cycling between 2.8–4.3 V and 2.8–4.5 V for 20 cycles. The XRD and electrochemical results suggested that cation mixing in this layered structure oxide could be causing degradation of the cell capacity.     

Effects of surface area on electrochemical performance of Li[Ni<Subscript>0.2</Subscript>Li<Subscript>0.2</Subscript>Mn<Subscript>0.6</Subscript>]O<Subscript>2</Subscript> cathode material

The effect of surface area on the electrochemical properties and thermal stability of Li[Ni_0.2Li_0.2Mn_0.6]O₂ powders was characterized using a charge/discharge cycler and DSC (Differential Scanning Calorimeter). The surface area of the samples was successfully controlled from ~4.0 to ~11.7 m² g⁻¹ by changing the molar ratio of the nitrate/acetate sources and adding an organic solvent such as acetic acid or glucose. The discharge capacity and rate capability was almost linearly increased with increase in surface area of the sample powder. A sample with a large surface area of 9.6–11.7 m² g⁻¹ delivered a high discharge capacity of ~250 mAh g⁻¹ at a 0.2 C rate and maintained 62–63% of its capacity at a 6 C rate versus a 0.2 C rate. According to the DSC analysis, heat generation by thermal reaction between the charged electrode and electrolyte was not critically dependent on the surface area. Instead, it was closely related to the type of organic solvent employed in the fabrication process of the powder.     

Enhanced electrochemical and storage properties of La2/3−XLi3XTiO3-coated Li[Ni0.4Co0.3Mn0.3]O2

A Li[Ni_0.4Co_0.3Mn_0.3]O₂ cathode was modified by applying a La_2/3−XLi_3XTiO₃ (LLT) coating. Transmission electron microscope (TEM) images reveal that the coating layer consists of nanoparticles. The coated cathode demonstrated an enhanced rate capability, discharge capacity, and cyclic performance than the uncoated cathode. However, the influence of the coating upon these electrochemical properties is highly dependent upon the composition of the LLT coating layer. Coating layers having high La and low Li contents, such as La_0.67TiO₃, effectively improved the rate capability of the cathode. However, coating layers with a low La and high Li content greatly enhanced the discharge capacity of the cathode under high cut-off voltage (4.8 V) conditions. Overall, the thermal stability of the Li[Ni_0.4Co_0.3Mn_0.3]O₂ electrode was improved by the LLT coating. Storage tests confirmed that the La_2/3−XLi_3XTiO₃ coating dramatically suppressed the dissolution of transition metals into the electrolyte.     

Preparation and electrochemical performance of Li-rich layered cathode material,Li[Ni<Subscript>0.2</Subscript>Li<Subscript>0.2</Subscript>Mn<Subscript>0.6</Subscript>]O<Subscript>2</Subscript>, for lithium-ion batteries

The Li-rich layered cathode material, Li[Ni_0.2Li_0.2Mn_0.6]O₂, was synthesized via a “mixed oxalate” method, and its structural and electrochemical properties were compared with the same material synthesized by the sol–gel method. X-ray diffraction (XRD) shows that the synthesized powders have a layered O₃–LiCoO₂-type structure with the R-3m symmetry. X-ray photoelectron spectroscopy (XPS) indicates that in the above material, Ni and Mn exist in the oxidation states of +2 and +4, respectively. The layered material exhibits an excellent electrochemical performance. Its discharge capacity increases gradually from the initial value of 228 mA hg⁻¹ to a stable capacity of over 260 mA hg⁻¹ after the 10th cycle. It delivers a larger capacity of 258 mA hg⁻¹ at the 30th cycle. The dQ/dV curves suggest that the increasing capacity results from the redox-reaction of Mn⁴⁺/Mn³⁺.     

Improved electrochemical properties of Li1+x(Ni0.3Co0.4Mn0.3)O2−δ (x = 0, 0.03 and 0.06) with lithium excess composition prepared by a spray drying method

Layered Li_1+x(Ni_0.3Co_0.4Mn_0.3)O_2−δ (x = 0, 0.03 and 0.06) materials were synthesized through the different calcination times using the spray-dried precursor with the molar ratio of Li/Me = 1.25 (Me = transition metals). The physical and electrochemical properties of the lithium excess and the stoichiometric materials were examined using XRD, AAS, BET and galvanostatic electrochemical method. As results, the lithium excess Li_1.06(Ni_0.3Co_0.4Mn_0.3)O_2−δ could show better electrochemical properties, such as discharge capacity, capacity retention and C rate ability, than those of the stoichiometric Li_1.00(Ni_0.3Co_0.4Mn_0.3)O_2−δ. In this paper, the effect of excess lithium on the electrochemical properties of Li_1+x(Ni_0.3Co_0.4Mn_0.3)O_2−δ materials will be discussed based on the experimental results of ex situ X-ray diffraction, transmission electron microscopy (TEM) and galvanostatic intermittent titration technique (GITT)     

Investigation of a new lead-free Bi<Subscript>0.5</Subscript>(Na<Subscript>0.40</Subscript>K<Subscript>0.10</Subscript>)TiO<Subscript>3</Subscript>-(Ba<Subscript>0.7</Subscript>Sr<Subscript>0.3</Subscript>)TiO<Subscript>3</Subscript> piezoelectric ceramic

Lead-free piezoelectric compositions of the (1-x)Bi_0.5(Na_0.40K_0.10)TiO₃-x(Ba_0.7Sr_0.3)TiO₃ system (when x = 0, 0.05, 0.10, 0.15, and 0.20) were fabricated using a solid-state mixed oxide method and sintered between 1,050°C and 1,175°C for 2 h. The effect of (Ba_0.7Sr_0.3)TiO₃ [BST] content on phase, microstructure, and electrical properties was investigated. The optimum sintering temperature was 1,125°C at which all compositions had densities of at least 98% of their theoretical values. X-ray diffraction patterns that showed tetragonality were increased with the increasing BST. Scanning electron micrographs showed a slight reduction of grain size when BST was added. The addition of BST was also found to improve the dielectric and piezoelectric properties of the BNKT ceramic. A large room-temperature dielectric constant, ε _r (1,609), and piezoelectric coefficient, d ₃₃ (214 pC/N), were obtained at an optimal composition of x = 0.10.     

Properties of LiNi<Subscript>0.8</Subscript>Co<Subscript>0.1</Subscript>Mn<Subscript>0.1</Subscript>O<Subscript>2</Subscript> as a high energy cathode material for lithium-ion batteries

Nickel-rich layered materials are prospective cathode materials for use in lithium-ion batteries due to their higher capacity and lower cost relative to LiCoO₂. In this work, spherical Ni_0.8Co_0.1Mn_0.1(OH)₂ precursors are successfully synthesized through a co-precipitation method. The synthetic conditions of the precursors - including the pH, stirring speed, molar ratio of NH₄OH to transition metals and reaction temperature - are investigated in detail, and their variations have significant effects on the morphology, microstructure and tap-density of the prepared Ni_0.8Co_0.1Mn_0.1 (OH)₂ precursors. LiNi_0.8Co_0.1Mn_0.1O₂ is then prepared from these precursors through a reaction with 5% excess LiOH· H₂O at various temperatures. The crystal structure, morphology and electrochemical properties of the Ni_0.8Co_0.1Mn_0.1 (OH)₂ precursors and LiNi_0.8Co_0.1Mn_0.1O₂ were investigated. In the voltage range from 3.0 to 4.3 V, LiNi_0.8Co_0.1Mn_0.1O₂ exhibits an initial discharge capacity of 193.0mAh g^-1 at a 0.1 C-rate. The cathode delivers an initial capacity of 170.4 mAh g^-1 at a 1 C-rate, and it retains 90.4% of its capacity after 100 cycles.     

Catalytic properties of Co<Subscript>3</Subscript>O<Subscript>4</Subscript> nanoparticles for rechargeable Li/air batteries

Three types of Co₃O₄ nanoparticles are synthesized and characterized as a catalyst for the air electrode of a Li/air battery. The shape and size of the nanoparticles are observed using scanning electron microscopy and transmission electron microscopy analyses. The formation of the Co₃O₄ phase is confirmed by X-ray diffraction. The electrochemical property of the air electrodes containing Co₃O₄ nanoparticles is significantly associated with the shape and size of the nanoparticles. It appears that the capacity of electrodes containing villiform-type Co₃O₄ nanoparticles is superior to that of electrodes containing cube- and flower-type Co₃O₄ nanoparticles. This is probably due to the sufficient pore spaces of the villiform-type Co₃O₄ nanoparticles.     

Synthesis,structural, and electrochemical performance of V<Subscript>2</Subscript>O<Subscript>5</Subscript> nanotubes as cathode material for lithium battery

Various vanadium oxide nanostructures are currently drawn interest for the potential applications of Li batteries, super capacitors, and electrochromic display devices. In this article, the synthesis of V₂O₅ nanotubes by hydrothermal method using 1-hexadecylamine (HDA) and PEO as a template and surface reactant were reported, respectively. The structural properties and electrochemical performances of these nanostructures were investigated for the application of Li batteries. Structure and morphology of the samples were investigated by XRD, FTIR, SEM, and TEM analysis. The battery with V₂O₅ nanotubes electrode showed initial specific capacity of 185 mAhg⁻¹, whereas the PEO surfactant V₂O₅ nanotubes exhibited 142 mAhg⁻¹. It was found that PEO surfactant V₂O₅ nanotubes material showed less specific capacity at initial stages but better stability was exhibited at higher cycle numbers when compared to that of V₂O₅ nanotubes. The cyclic performance of the PEO surfactant material seems to be improved with the role of polymeric component due to its surface reaction with V₂O₅ nanotubes during the hydrothermal process.     

The electrochemical performance of a La-Mg-Ni-Co-Mn metal hydride electrode alloy in the temperature range of −20 to 30 °C

The effect of temperature on the overall electrochemical properties of La_0.7Mg_0.3Ni_2.875Co_0.525Mn_0.1 hydrogen storage alloy has been studied systematically. The results show that temperature has a striking effect on the overall electrochemical properties, especially the electrochemical kinetic performance. The maximum discharge capacity and the high rate dischargeability (HRD) of La_0.7Mg_0.3Ni_2.875Co_0.525Mn_0.1 alloy electrode both decrease with decreasing test temperature, mainly due to the slower hydrogen transfer in the bulk of the alloy and the lower electrocatalytic activity at lower temperatures. Detailed studies on the temperature effect on the polarization resistance (R_D), the exchange current density (I₀), the limiting current density (I_L) and the hydrogen diffusion coefficient (D), indicate that the diffusion of hydrogen in the bulk for La-Mg-Ni-Co system hydrogen storage alloy electrodes is the rate-determining factor for the discharge process of the alloy electrode for the temperature over 10 °C and the charge-transfer reaction is rate-determining step at lower temperature.     

Carbon nanotube/Co<Subscript>3</Subscript>O<Subscript>4</Subscript> composite for air electrode of lithium-air battery

A carbon nanotube [CNT]/Co₃O₄ composite is introduced as a catalyst for the air electrode of lithium-air [Li/air] batteries. Co₃O₄ nanoparticles are successfully attached to the sidewall of the CNT by a hydrothermal method. A high discharge capacity and a low overvoltage indicate that the CNT/Co₃O₄ composite is a very promising catalyst for the air electrode of Li/air batteries.     

Structural characterization and electrochemical properties of Co<Subscript>3</Subscript>O<Subscript>4</Subscript> anode materials synthesized by a hydrothermal method

Cobalt oxide [Co₃O₄] anode materials were synthesized by a simple hydrothermal process, and the reaction conditions were optimized to provide good electrochemical properties. The effect of various synthetic reaction and heat treatment conditions on the structure and electrochemical properties of Co₃O₄ powder was also studied. Physical characterizations of Co₃O₄ are investigated by X-ray diffraction, scanning electron microscopy, and Brunauer-Emmett-Teller [BET] method. The BET surface area decreased with values at 131.8 m²/g, 76.1 m²/g, and 55.2 m²/g with the increasing calcination temperature at 200°C, 300°C, and 400°C, respectively. The Co₃O₄ particle calcinated at 200°C for 3 h has a higher surface area and uniform particle size distribution which may result in better sites to accommodate Li⁺ and electrical contact and to give a good electrochemical property. The cell composed of Super P as a carbon conductor shows better electrochemical properties than that composed of acetylene black. Among the samples prepared under different reaction conditions, Co₃O₄ prepared at 200°C for 10 h showed a better cycling performance than the other samples. It gave an initial discharge capacity of 1,330 mAh/g, decreased to 779 mAh/g after 10 cycles, and then showed a steady discharge capacity of 606 mAh/g after 60 cycles.     

LiNi<Subscript>0.4</Subscript>Co<Subscript>0.3</Subscript>Mn<Subscript>0.3</Subscript>O<Subscript>2</Subscript> thin film electrode by aerosol deposition

LiNi_0.4Co_0.3Mn_0.3O₂ thin film electrodes are fabricated from LiNi_0.4Co_0.3Mn_0.3O₂ raw powder at room temperature without pretreatments using aerosol deposition that is much faster and easier than conventional methods such as vaporization, pulsed laser deposition, and sputtering. The LiNi_0.4Co_0.3Mn_0.3O₂ thin film is composed of fine grains maintaining the crystal structure of the LiNi_0.4Co_0.3Mn_0.3O₂ raw powder. In the cyclic voltammogram, the LiNi_0.4Co_0.3Mn_0.3O₂ thin film electrode shows a 3.9-V anodic peak and a 3.6-V cathodic peak. The initial discharge capacity is 44.6 μAh/cm², and reversible behavior is observed in charge-discharge profiles. Based on the results, the aerosol deposition method is believed to be a potential candidate for the fabrication of thin film electrodes.     

Comparative study of the preparation and electrochemical performance of LiNi<Subscript>1</Subscript><Subscript>/2</Subscript>Mn<Subscript>1/2</Subscript>O<Subscript>2</Subscript> electrode material for rechargeable lithium batteries

Positive electrode material LiNi_1/2Mn_1/2O₂ was synthesized via the carbonate co-precipitation method and the hydroxide precipitation route to study the effects of the precursor on its structural and electrochemical properties. The results of X-ray diffraction and Rietveld refinement show that the carbonate precursor of Ni²⁺ and Mn²⁺ exhibits one phase at a pH of 8.5, while the hydroxide deposit separates into Ni(OH)₂ and Mn(OH)₂ phases under the same experimental conditions. LiNi_1/2Mn_1/2O₂ material prepared from the hydroxide precursor shows 8.9% Li/Ni exchange and a large capacity loss of 11.3% in the first 10 cycles. By contrast, more uniform distribution of transition metal ions and stable Mn²⁺ in the carbonate precursor contribute to only 7.8% Li/Ni disorder in the obtained LiNi_1/2Mn_1/2O₂, which delivers a reversible capacity of about 182 mAh g⁻¹ at a current rate of 14 mA g⁻¹ between 2.5 and 4.8 V.     

Electrochemical performances of Mm0.7MgxNi2.58Co0.5Mn0.3Al0.12 (x = 0, 0.3) hydrogen storage alloys in the temperature range from 238 to 303 K

A series of experiments have been performed to investigate electrochemical properties of Mm_0.7Mg_xNi_2.58Co_0.5Mn_0.3Al_0.12 (x = 0, 0.3) alloy at various temperatures (238 K, 273 K and 303 K). The results indicate that both alloy electrodes exhibit high dischargeabilities after elemental substitution, above 320 mAh g^?1 even at 238 K. The capacity degradation of the two alloys are primarily ascribed to serious pulverization, other than the oxidation of active components at the initial stage. Moreover, the electrochemical performances of Mm_0.7Mg_xNi_2.58Co_0.5Mn_0.3Al_0.12 (x = 0, 0.3) alloy electrodes depend on the alloy type and testing temperature. Mm_0.7Mg_0.3Ni_2.58Co_0.5Mn_0.3Al_0.12 alloy, consisting of LaNi₅-phase and La₂Ni₇-phase, shows better properties of discharge capacity, cyclic stability, self-discharge and pulverization resistance at the three temperatures than those of single LaNi₅-phase Mm_0.7Ni_2.58Co_0.5Mn_0.3Al_0.12 alloy. The electrochemical kinetics studies indicate that the activation energy of hydrogen diffusion and exchange current density (I₀) of Mm_0.7Mg_0.3Ni_2.58Co_0.5Mn_0.3Al_0.12 alloy are lower than those of Mm_0.7Ni_2.58Co_0.5Mn_0.3Al_0.12 alloy. When the temperature increases from 238 to 303 K, the capacity loss, high-rate dischargeability, exchange current density I₀ and hydrogen diffusion coefficient (D/a²) of the two alloys increases, while capacity retention decreases. Further analysis of kinetics suggests that bulk hydrogen diffusion is the rate-determining step of the battery reaction at low temperature 238 K, and charge-transfer reaction on alloy surface is the rate-determining step when tested at 273 K and 303 K for both alloys. The perfect low temperature discharge capacities of the two alloys can mainly attribute to the decrease of activation energy for hydrogen diffusion after elemental substitution.     

Electrical properties of lead-free 0.98(Na<Subscript>0.5</Subscript>K<Subscript>0.5</Subscript>)NbO<Subscript>3</Subscript>-0.02Ba(Zr<Subscript>0.52</Subscript>Ti<Subscript>0.48</Subscript>)O<Subscript>3</Subscript> piezoelectric ceramics by optimizing sintering temperature

Lead-free 0.98(Na_0.5K_0.5)NbO₃-0.02Ba(Zr_0.52Ti_0.48)O₃ [0.98NKN-0.02BZT] ceramics were fabricated by the conventional mixed oxide method with sintering temperature at 1,080°C to 1,120°C. The results indicate that the sintering temperature obviously influences the structural and electrical properties of the sample. For the 0.98NKN-0.02BZT ceramics sintered at 1,080°C to 1,120°C, the bulk density increased with increasing sintering temperature and showed a maximum value at a sintering temperature of 1,090°C. The dielectric constant, piezoelectric constant [d ₃₃], electromechanical coupling coefficient [k _p], and remnant polarization [P _r] increased with increasing sintering temperature, which might be related to the increase in the relative density. However, the samples would be deteriorated when they are sintered above the optimum temperature. High piezoelectric properties of d ₃₃ = 217 pC/N, k _p = 41%, dielectric constant = 1,951, and ferroelectric properties of P _r = 10.3 μC/cm² were obtained for the 0.98NKN-0.02BZT ceramics sintered at 1,090°C for 4 h.     

Voltammetric behavior and the determination of quercetin at a flowerlike Co<Subscript>3</Subscript>O<Subscript>4</Subscript> nanoparticles modified glassy carbon electrode

Flowerlike Co₃O₄ nanoparticles were used as a modifier on the glassy carbon electrode to fabricate a quercetin (Qu) sensor. The morphology and crystallinity of the prepared Co₃O₄ material were investigated by scanning electron microscopy and X-ray diffraction. Electrochemical behavior of Qu at the sensor was studied by cyclic voltammetry and semi-derivative voltammetry. Results suggested that the modified electrode exhibited a strong electrocatalytic activity toward the redox of Qu. The electron transfer coefficient (α), the number of electron transfer (n), and the diffusion coefficient (D) of Qu at the sensor were calculated. Under the optimum conditions, the catalytic peak currents of Qu were linearly dependent on the concentrations of Qu in the range from 5.0 × 10⁻⁷ to 3.3 × 10⁻⁴ M, with a detection limit of 1.0 × 10⁻⁷ M. This proposed method was successfully applied to determine the quercetin concentration in Ginkgo leaf tablet and human urine samples.     

Preparation and Characterization of LiNi<Subscript>0.8</Subscript>Co<Subscript>0.2</Subscript>O<Subscript>2</Subscript> Synthesized by an Emulsion Drying Method

A layered LiNi_0.8Co_0.2O₂ solid solution, which is a promising cathode material for secondary lithium batteries, was successfully synthesized by an emulsion drying method. Because electrochemical properties significantly depend on the conditions of the synthesis, the calcination temperature was carefully determined on the basis of X-ray diffraction and TG studies. The prepared cathodes were characterized by means of SEM, BET, X-ray diffraction, Rietveld refinement, cyclic voltammetry and a charge-discharge experiment. From the Rietveld analysis, it was found that powder calcined at 800 °C for 12 h exhibits a well ordered and lower cation mixed layered structure than the others. The cyclic voltammetry experiment shows that phase transformation can be suppressed considerably by increasing the calcination temperature to 800 °C. The highest discharge capacity of 188.4 mA h g⁻¹ was obtained from the sample prepared at 800 °C. Furthermore, a high capacity retention ratio of 88.1% was found for the initial value after 50 cycles at a constant current density of 40 mA g⁻¹ between 2.7 V_Li/Li⁺ and 4.3 V_Li/Li⁺. In the rate capability test, the cathode delivered a higher discharge capacity of 153.1 mA h g⁻¹ at a 4 C (800 mA g⁻¹) rate.     

Core–shell NTC materials with low thermal constant and high resistivity for wide-temperature thermistor ceramics

Core–shell structures have been proposed to improve the electrical properties of negative-temperature coefficient (NTC) thermistor ceramics. In this work, Al₂O₃-modified Co_1.5Mn_1.2Ni_0.3O₄ NTC thermistor ceramics with adjustable electrical properties were prepared through citrate-chelation followed by conventional sintering. Co_1.5Mn_1.2Ni_0.3O₄ powder was coated with a thin Al₂O₃ shell layer to form a core–shell structure. Resistivity (ρ) increased rapidly with increasing thickness of the Al₂O₃ layer, and the thermal constant (B) varied moderately between 3706 and 3846 K. In particular, Co_1.5Mn_1.2Ni_0.3O₄@Al₂O₃ ceramic with 0.08 wt% Al₂O₃ showed the increase of ρ double, and the change in its B was less than 140 K. The Co_1.5Mn_1.2Ni_0.3O₄@Al₂O₃ NTC ceramics showed high stability, and their grain size was relatively uniform due to the protection offered by the shell. The aging coefficient of the ceramic was less than 0.2% after aging for 500 hours at 125°C. Taken together, the results indicate that as-prepared Co_1.5Mn_1.2Ni_0.3O₄@Al₂O₃ NTC ceramics with a core–shell structure may be promising candidates for application as wide-temperature NTC thermistor ceramics.