The electronic conductivity of Ba0.5Sr0.5CoxFe1?xO3?δ (BSCF: x?=?0?～?1.0) under different oxygen partial pressures

The electronic conductivity of sintered BSCF ceramics (Ba_0.5Sr_0.5Co _x Fe_1−x O_3−δ, 0 ≤  x  ≤ 1) was measured as a function of temperature up to 1273 K in air. The conductivity of BSC is thermally activated over 298–1273 K with an activation energy of 0.21 eV. The conductivity of BSF and BSCF (0.2 ≤  x  ≤ 0.8) is thermally activated below ∼673 K with activation energies of 0.21 eV–0.40 eV. Above 673 K, the formation of oxygen vacancies results in a decrease in p-type carrier concentration and a decrease in electronic conductivity. Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3−δ (BSCF5582) was also measured under 10⁻⁵ atm ≤ pO₂ ≤ 1 atm. Below ∼673 K, the electronic conductivity of BSCF 5582 shows no dependence on pO₂. Above 673 K, the conductivity of BSCF5582 increases with increasing pO₂ for pO₂ ≥ 0.01 (p-type conduction) and decreases slightly with increasing pO₂ for pO₂  ≤ 0.01 atm. The activation energy for conduction above ∼673 K and at pO₂ ≥ 0.1 is ∼0.07 eV. Above ∼823K and at pO₂ ≥ 0.01 atm, the activation energy for conduction is ∼0.2 eV.     

Grain growth kinetics of textured 0.92Na0.5Bi0.5TiO3—0.08BaTiO3 ceramics by tape casting with Bi2.5Na3.5Nb5O18 templates

Plate-like Bi_2.5Na_3.5Nb₅O₁₈ particles were used as templates to fabricate grain-oriented Na_0.5Bi_0.5TiO₃—BaTiO₃ (NBTBT) ceramics by reactive-templated grain growth. The effects of sintering conditions on the grain orientation and microstructure of the textured NBTBT ceramics were investigated, and the kinetic mechanism of grain growth is discussed. The results show that textured ceramics were successfully obtained with orientation factor more than 0.6. NBTBT specimens are composed of strip-like grains and equiaxed shaped grains. The textured ceramics have a microstructure with strip-like grains aligning in the direction parallel to the casting plane and exhibit an {h00} preferred orientation. The degree of grain orientation increases initially, then decreases with increasing sintering temperature and soaking time. The maximum texture fraction is 0.69 when sintered at 1185 °C for 6 h. The kinetic exponent n and activation energy Q of the two types of grain in textured NBTBT ceramics were calculated. The results show that the grain growth mechanism of oriented grains is controlled not only by grain lattice diffusion, but also by grain boundary diffusion. The grain growth mechanism of matrix grains is mainly controlled by the grain boundary curvature.     

Synthesis of (Ba0.5Sr0.5)(Ti1 − x Zr x )O3 ceramics: Effect of Zr content on room temperature electrical properties

The phase formation behavior and room temperature dielectric properties of bulk perovskite solid solution composition (Ba_0.5Sr_0.5)(Ti_1 − x Zr _x )O₃ have been investigated. The samples with different Zr-content were prepared through solid state reaction. The XRD investigation showed that Zr⁺⁴ is systematically dissolved in Ba_0.5Sr_0.5TiO₃ lattice up to about 60 atm.% substitution, having cubic Pm3m structure. Eighty atom percent Zr substituted composition showed to contain a cubic phase similar to that of x = 0.6 composition and a tetragonal (I4/mcm) phase. That is the solid solution breaks around at 80 atm.% Zr substitutions. Ba_0.5Sr_0.5ZrO₃ was having orthorhombic Imma structure. Decrease in grain sizes were observed with increase in Zr content. The permittivity of the ceramics decreased with the increase in Zr substitution. The frequency dependency of dielectric loss in the frequency range 10 Hz to 10 MHz, were improved with Zr substitution in the ceramics. The room temperature ac and dc conductivity also decreased significantly with the increase in Zr-content.     

锂离子电池高镍三元正极材料LiNi1-x-yCoxMnyO2的改性研究进展

新能源产业的快速发展对储能材料与器件的综合性能提出了更高的要求。锂离子电池正极材料,尤其是高镍三元材料（LiNi_1-x-yCo_xMn_yO₂）具有高能量密度、高工作电压及优异的化学稳定性等特点,因而被认为是下一代动力电池商业化正极材料的优越选择。系统总结了高镍三元材料LiNi_1-x-yCo_xMn_yO₂的优势并指出了其亟待解决的问题;在此基础上,综述了其各类改性方法,包括各类阴阳离子掺杂、表面包覆、浓度梯度材料设计以及石墨烯复合等方法;最后对其发展方向及商业化应用进行了展望。     

Effect of Zr/Ti ratio on piezoelectric and dielectric properties of PNW–PMS–PZT ceramics

(Pb_0.95Sr_0.05)[(Ni_1/2W_1/2)_0.02(Mn_1/3Sb_2/3)0.06(Zr_XTi_Y)_0.92]O₃ piezoelectric ceramics (abbreviated as PNW–PMS–PZT) with 1%mol excess PbO, 0.25 wt% CeO₂ and 0.2 wt% MnO₂ were prepared by traditional ceramics process. The phase structure of ceramics sintered at 1150°C were analyzed. Results show that the pure perovskite phase was in all ceramics specimens, the phase structure of PNW–PMS–PZT piezoelectric ceramics was transformed from tetragonal to rhombohedral, with Zr/Ti ratio increased in system; Effect of Zr/Ti ratio on piezoelectric and dielectric properties was investigated. Results show that ? _r , tanδ, k _p and d ₃₃ increased with an increase of Zr/Ti ratio and reached the maximum values at Zr/Ti ratio of 50/50, then decreased with further increase of Zr/Ti ratio, whereas the variation of Q _m with an increase of Zr/Ti ratio showed the opposite trend, T _c showed a tendency to decrease with an increase of Zr/Ti ratio. The piezoelectric ceramics with Zr/Ti ratio of 50/50 was applied in high-power multilayer piezoelectric transformer, and properties parameter were ? _r ?=?2100, tanδ?=?0.006, k _p ?=?0.613, Q _m ?=?1300, d ₃₃ ?=?380pC/N, T _c ?=?205 °C.     

Effects of doping Y2O3 on the microstructure and electrical properties of ZnO-Bi2O3−based varistor ceramics

ZnO-based varistor ceramics doped with different amount of Y₂O₃ have been made by two-step solid-state reaction route including the pre-calcination and subsequent sintering procedures, using nanosized ZnO powder and corresponding additives as the raw material. The phase composition, microstructure and electrical properties were studied by means of X-ray diffractometry (XRD), scanning electron microscopy (SEM) and direct current electrical measurement. It was found that the electrical properties of the varistor ceramics sintered at 950 °C from the powder pre-calcined at 800 °C were enhanced by doped appropriate amount of Y₂O_3. Particularly, ZnO varistors doped with 1.2 mol% Y₂O₃ possessed the best comprehensive electrical properties with the breakdown field of 2113 V/mm, the nonlinear coefficient of 184.6 and the leakage current of 0.4 μA. Y₂O₃ phase, Y-rich phase and the other secondary phase particles were confirmed to distribute along the grain boundaries of predominant ZnO grains from XRD and SEM analyses. The results illustrated that doping Y₂O₃ should be a promising route to obtain varistor ceramics with excellent electrical properties.

     

Effect of sintering temperature on microstructure and piezoelectric properties of Pb-free BiFeO3–BaTiO3 ceramics in the composition range of large BiFeO3 concentrations

Lead-free (1-x)BiFeO₃–xBaTiO₃ [(1-x)BF-xBT] piezoelectric ceramics in the range of large BF concentrations were prepared by conventional oxide-mixed method at various sintering temperatures. The sintering temperatures have a significant effect on the microstructure of the ceramics, and the composition has a remarkable effect on optimal sintering temperature of the ceramics, which are closely related with piezoelectric properties. The grain size increased with increasing sintering temperature and the optimal sintering temperature increased with increasing BT content. The ceramics with x?=?0.275 sintered at 990 °C exhibit enhanced electrical properties of d ₃₃?=?136pC/N and k _p?=?0.312 due to the polarization rotation mechanisms at MPB and desired microstructure. These results show that the ceramic with x?=?0.275 is a promising lead-free high-temperature piezoelectric material.     

Structural evolution and microwave dielectric properties of (1 − x)BaZn1/3Nb2/3O3 + xBaMg1/2W1/2O3 ceramics

Structural evolution and microwave dielectric properties of (1 − x)BaZn_1/3Nb_2/3O₃ + xBaMg_1/2W_1/2O₃ (0 ≤ x ≤ 1) system have been investigated in this work. All samples exhibit single perovskite phase except for the samples with x = 0 and x ≥ 0.8 in which barium niobate and BaWO₄ second phase existed, respectively. 1:1 cations ordering existed in the samples with x ≥ 0.1, and the ordering degree increases with the increase of x. Liquid phase sintering was observed in the sample with x ≥ 0.8. Dielectric constant decreases almost linearly from 40.8 to 17.4 with increasing x. Q × f value monotonically increases from 26,162 GHz to 64,705 GHz with increasing x. The τ_f value changes from +30 ppm/°C to −27.8ppm/°C. Near zero τ_f value of −1.4 ppm/°C could be obtained at x = 0.4 composition.     

Investigation of the BaTiO3–BaMg1/3Nb2/3O3 system: Structural, dielectric, ferroelectric and electromechanical studies

Lead-free (1?x) BaTiO₃ –x BaMg_1/3Nb_2/3O₃ ceramics with x?=?0.03, 0.04, 0.05 and 0.06 were prepared by solid-state synthesis. The effects of the Ba(Mg_1/3Nb_2/3)O₃ addition on the phase composition, dielectric and ferroelectric properties, as well as the electromechanical response of the classic ferroelectric BaTiO₃ were investigated. The room-temperature X-ray diffraction analyses of all the ceramics revealed a perovskite phase after sintering at 1300 °C with a composition-dependent symmetry. The samples with a lower concentration of Ba(Mg_1/3Nb_2/3)O₃, i.e., x?=?0.03 and 0.04, were tetragonal, while the samples with x?=?0.05 and 0.06 were found to be cubic. The result is in agreement with the dielectric, ferroelectric and electromechanical properties. With x increasing from 0.03 to 0.06 the temperature of the diffused maximum of the dielectric permittivity decreased from 348 K to 265 K. All the ceramics showed a large electromechanical response: the calculated room-temperature electrostrictive coefficient M ₃₃ of the sample with x?=?0.06 was 1.4 · 10^?16?m²/V², which is comparable to the value measured for Pb(Mg_1/3Nb_2/3)O₃ ceramics.     

Synthesis, electrical and thermal properties of Bi4V2−xZrxO11 (x = 0.0, 0.02, 0.06 and 0.10) ceramics

Polycrystalline ceramic samples of Bi₄V_2?xZr_xO₁₁ (x?=?0.0, 0.02, 0.06 and 0.10) have been synthesized by standard solid state reaction method using high purity oxides. The formation of the compounds have been checked by X-ray diffraction method. The dielectric constant, dielectric loss and ac conductivity as a function of frequency and temperature have been measured. The dielectric studies indicate that the material is highly lossy and hence its ac conductivity increases with the increase of temperature. The dc conductivity of all the materials has been measured as a function of temperature from room temperature to 673 K and its activation energy was calculated using the relation σ?=?σ_oexp (?Ea/kT). The Modulated Differential Scanning Calorimetry (MDSC) has been used to investigate the effect of substitution on the heat capacity and heat flow of the compounds. The results are discussed in detail.     

Effect of additive SrWO4 on microwave dielectric properties of SrTiO3–Sr(Mg1/3Nb2/3)O3 ceramics

The crystal structure and the properties of a new microwave dielectric ceramics x SrTiO₃–(1???x)Sr(Mg_1/3Nb_2/3)O₃ have been investigated. With x?=?0.025, The new microwave dielectric ceramic achieves the dielectric properties of a dielectric constant ? _r ～27.8, a Q?×?f value ～26,800, and a τ _f value ～7.4 ppm/°C. When the SrWO₄ is added, the sintering temperature of x SrTiO₃–(1???x)Sr(Mg_1/3Nb_2/3)O₃ ceramics will fall to 1350 °C, and its Q?×?f value can be improved further and the τ _f value becomes smaller. When the SrWO₄ is added by 0.07 mol, the specimen acquires the following microwave properties: a dielectric constant ? _r ～30.3, a Q?×?f value ～29,500, and a τ _f value of approximately ?0.4 ppm/°C.     

Study of the electrical properties of Pb(Zn,Ni)1/3Nb2/3O3–PbTiO3 ceramics across the morphotropic phase boundary

Structure and electrical properties of (1???x)Pb(Zn_0.2Ni_0.8)_1/3Nb_2/3O₃–xPbTiO₃ ceramics with x?=?0.24–0.38 were examined in detail. X-ray diffraction measurements reveal that all samples are in pure perovskite phase, and most of them lie within the morphotropic phase boundary (MPB) region. The dielectric behaviors of all compositions are characterized with diffuse phase transition and frequency dispersion. The variable power law and the Vogel–Fulcher relation have been used to describe such dielectric behaviors. The highest dielectric constant and the largest piezoelectric coefficient are simultaneously observed when x?=?0.30. The variation of the ferroelectric property with PT content is also discussed.     

Structural,morphological and electrical properties of new type Dy doped Ca6-xNa2Y2(SiO4)6(OH)2 hydroxyapatite compound synthesized by co – precipitation method

Journal of Electroceramics - In this study Dy3+ doped Ca6-xNa2Y2(SiO4)6(OH)2 (x?=?0 – 0.05 mol%) hydroxyapatite compound was synthesized by co – precipitation...     

Piezoelectric and dielectric properties of low temperature sintering Pb(Mn1/3Nb2/3)O3–Pb(Zn1/3Nb2/3)O3–Pb(Zr0.48Ti0.52)O3 ceramics with variation of sintering time

Pb(Mn_1/3Nb_2/3)O₃–Pb(Zn_1/3Nb_2/3)O₃–Pb(Zr_0.48Ti_0.52)O₃ (abbreviated as PMN–PZN–PZT) ceramics containing Li₂CO₃, Bi₂O₃ and CuO as sintering aids were fabricated using two-stage calcinations method in order to develop low temperature sintering ceramics for multilayer piezoelectric actuators. Their dielectric and piezoelectric properties were investigated according to the variation of sintering time. All the specimens sintered at 930°C for 60~150 min showed tetragonal phases without secondary phases. Electromechanical coupling factor (kp), dielectric constant (ε _r) and piezoelectric constant (d ₃₃) increased with the increase of the sintering time. The mechanical quality factor (Qm) exhibited maximum of 1,815 with the increase of sintering time for 120 min and then slightly decreased. At the sintering temperature of 930°C and the sintering time of 120 min, the optimal values such as the density of 7.69 g/cm³, kp of 0.516, ε _r of 1158, Qm of 1815, and d ₃₃ of 287 pC/N were found for multilayer piezoelectric actuators.     

Piezoelectric properties of MnO2 doped low temperature sintering Pb(Mn1/3Nb2/3)O3–Pb(Ni1/3Nb2/3)O3–Pb(Zr0.50Ti0.50)O3 ceramics

In this study, in order to develop the composition ceramics for low loss and low temperature sintering multilayer piezoelectric actuator, Pb(Mn_1/3Nb_2/3)O₃–Pb(Ni_1/3Nb_2/3)O₃–Pb(Zr_0.50Ti_0.50)O₃ (abbreviated as PMN-PNN-PZT) ceramics were fabricated using Li₂CO₃ and Na₂CO₃ as sintering aids, and their piezoelectric and dielectric characteristics were investigated according to the amount of MnO₂ addition. At the 0.2 wt% MnO₂ doped specimen sintered at 900 °C, density and mechanical quality factor (Q _m) showed the maximum values of 7.81[g/cm³]and 1186, respectively. And also, at 0.1 wt% MnO₂ doped specimen, electromechanical coupling factor (k _p), piezoelectric constant (d ₃₃) of specimen showed the maximum values of 0.608 and 377[pC/N], respectively. Dielectric constant (? _r) slightly decreased with increasing MnO₂. Taking into consideration the density of 7.81[g/cm³], electromechanical coupling factor (k _p)of 0.597 the mechanical quality factor (Q _m) of 1,186, and piezoelectric constant (d ₃₃) of 356[pC/N], it could be concluded that 0.2 wt% MnO₂ doped composition ceramics sintered at 900 °C was best for low loss and low temperature sintering multilayer piezoelectric actuator application.     

Effect of CuO addition on sintering temperature and piezoelectric properties of 0.05Pb(Al0.5Nb0.5)O3−0.95Pb(Zr0.52Ti0.48)O3+0.7 wt.% Nb2O5 + 0.5 wt.% MnO2 ceramics

Effect of CuO addition on piezoelectric properties of 0.05Pb(Al_0.5Nb_0.5)O₃?0.95Pb(Zr_0.52Ti_0.48)O₃+0.7 wt.% Nb₂O₅ + 0.5 wt.% MnO₂ (PAN-PZT) ceramics was studied to decrease the sintering temperature below 900°C for LTCC. The PAN-PZT ceramics sintered at 1200°C had piezoelectric properties of d ₃₃ = 340 pC/N, k _p = 61.6%, Q _m = 1,725, and density of 7.5 g/cm³. The addition of CuO significantly decreased the sintering temperature due to the formation of liquid phase containing a binary combination of PbO and CuO in grain boundary. Piezoelectric properties of d ₃₃ = 361 pC/N, k _p = 57%, Q _m = 145, and density of 7.8 g/cm³ were achieved at sintering temperature of 900°C. The CuO doped PAN-PZT ceramics show high density and d ₃₃ at low sintering temperature though its electromechanical quality factor abruptly decreases due to the CuO additive effect.     

Microstructure and microwave dielectric properties of (1 − x)Ca(Mg1/3Nb2/3)O3/xCa0.61Nd0.26TiO3 complex perovskite ceramics

Ceramics in the (1?x)Ca(Mg_1/3Nb_2/3)O₃/xCa_0.61Nd_0.26TiO₃ system were prepared and characterized. Single phase solid solutions were obtained up to x?=?0.4, and the crystal structure belonged to monoclinic space group P21(4) for x?=?0.1 and orthorhombic space group Pbnm(62) for x above 0.1. The secondary phase of Ca₂(Ti,Nb)₂O₆ was observed for x?=?0.6 and 0.8. Good combination of microwave dielectric properties was achieved in the present ceramics with x?=?0.4: ? _r?=?46.5, Qf?=?14,136 GHz, τ _f?=??12.5 ppm/°C.