Stress-dependent ferroelectric properties of Pb(Zr1/2Ti1/2)O3–Pb(Zn1/3Nb2/3)O3 ceramic systems

Effects of compressive stress on the ferroelectric properties of ceramics in PZT–PZN systems were investigated. (1 − x)Pb(Zr_1/2Ti_1/2)O₃(xPb(Zn_1/3Nb_2/3)O₃ or (1 − x)PZT–(x)PZN (x = 0.1–0.5) ceramics were prepared by a conventional mixed-oxide method. The ferroelectric properties under compressive stress of the PZT–PZN ceramics were observed at stress levels up to 170 MPa using a compressometer in conjunction with a modified Sawyer–Tower circuit. It was found that with increasing compressive stress the area of the ferroelectric hysteresis (P–E) loops, the saturation polarization (P_sat), the remanent polarization (P_r), and the coercive field (E_c) decreased. These results were interpreted through the non-180° ferroelectric domain switching processes.     

Internal bias field relaxation in poled Mn-doped Pb(Mn1/3Sb2/3)O3–Pb(Zr,Ti)O3 ceramics

The frequency, electric field cycling and temperature dependences of the polarization–electric field (P–E), strain–electric field (S–E) loops in poled Mn-doped 0.05Pb(Mn_1/3Sb_2/3)O₃–0.50PbZrO₃–0.45PbTiO₃ ceramics have been investigated. The P–E and S–E loops are strongly asymmetric corresponding to the presence of an internal bias field E_i after poling and aging, indicating that the domain walls are strongly pinned by preferentially oriented defect dipoles formed by the acceptor dopant ions (Mn²⁺/Mn³⁺) and O²⁻ vacancies. Whereas, the loops exhibit a tendency of changing from asymmetric shapes to normal symmetric ones with increasing electric field amplitude or decreasing frequency. Repeated electric field cycling as well as high temperature results in a similar effect. Meanwhile, the E_i reduces consequently, providing evidence of domain depinning or internal bias field relaxation. It is suggested that the reorientation of the defect dipoles and depinning of domain walls arising from high temperature or electric field cycling are responsible for this extrinsic internal bias field relaxation process.     

Dielectric characters of 0.7Pb(Mg1/3Nb2/3)O3–0.3PbTiO3 ceramics fabricated at ultra-low temperature by the spark-plasma-sintering method

Solid solution (1 − x)Pb(Mg_1/3Nb_2/3)O₃–xPbTiO₃ shows high dielectric constant near room temperature and is an ideal capacitor material. The composition 0.7Pb(Mg_1/3Nb_2/3)O₃–0.3PbTiO₃, which is located near the morphotropic phase boundary, were densified by the spark-plasma-sintering method at an ultra-low temperature (700 °C). Dielectric constant measurement shows that the thus prepared sample shows higher dielectric constant at room temperature and good temperature stability in a wide temperature range. The behavior is much different from that of samples sintered by conventional method and could be ascribed to size effect.     

Depolarization temperature and piezoelectric properties of (Bi1/2Na1/2)TiO3–(Bi1/2Li1/2)TiO3–(Bi1/2K1/2)TiO3 lead-free piezoelectric ceramics

The phase transition temperature and piezoelectric properties of x(Bi_1/2Na_1/2)TiO₃–y(Bi_1/2Li_1/2)TiO₃–z(Bi_1/2K_1/2)TiO₃ [x + y + z = 1] (abbreviated as BNLKT100y–100z) ceramics were investigated. BNLKT100y–100z ceramics were prepared by conventional ceramic fabrication. The depolarization temperature T_d was determined by the temperature dependence of the dielectric and piezoelectric properties. This study focuses on the effect of Li¹⁺ and K¹⁺ ions on T_d and the piezoelectric properties of BNT ceramics. BNLKT100y–100z (y = 0–0.08) has a morphotropic phase boundary (MPB) between rhombohedral and tetragonal phases at z = 0.18–0.20, and high piezoelectric properties were obtained at the MPB composition. The piezoelectric constant d₃₃ increased with increasing y; however, T_d decreased above y = 0.06. The d₃₃ and T_d values of BNLKT4-20 and BNLKT8-20 were 176 pC/N and 171 °C, and 190 pC/N and 115 °C, respectively.     

Bi(Zn1/2Ti1/2)O3 modified BiFeO3–BaTiO3 lead-free piezoelectric ceramics with high temperature stability

Lead-free high-temperature ceramics with compositions of 0.71BiFe_1−x(Zn_1/2Ti_1/2)_xO₃–0.29BaTiO₃ (BFZTx–BT, x=0–0.05 mol fraction) were fabricated by a conventional solid state reaction method. The effect of Bi(Zn_1/2Ti_1/2)O₃ (BZT) addition on the microstructure, electrical properties, relaxor behavior, and temperature stability has been studied. XRD patterns revealed that all compositions formed a single perovskite phase of pseudo-cubic crystal structure. The grain size was slightly affected by BZT addition. The diffuse phase transition and strong frequency dispersion of dielectric permittivity are observed for BZT modified ceramics. The addition of BZT into BFZTx–BT was also found to affect the piezoelectric properties and temperature stability of the ceramics with maximum values observed for x=0.5% and 1% BFZTx–BT compositions, respectively. The optimum piezoelectric properties with d₃₃=163 pC/N, together with high-temperature stability with a depolarization temperature T_d∼380 °C, reveal the BFZTx–BT ceramics to be promising high-temperature Pb-free piezoelectric materials.     

The characteristics of Ni–Co–Mn–O precursor and Li(Ni1/3Co1/3Mn1/3)O2 cathode powders prepared by spray pyrolysis

Ni–Co–Mn–O precursor powders with spherical shape and dense structure were prepared by spray pyrolysis from a spray solution containing a drying control chemical additive (DCCA) and polymeric precursors. In contrast, the Ni–Co–Mn–O precursor powders obtained from a spray solution without additives had a hollow and porous morphology. Ni–Co–Mn–O precursor powders with a spherical shape and dense structure yielded Li(Ni_1/3Co_1/3Mn_1/3)O₂ cathode powders with a spherical shape and fine size by means of a solid-state reaction with lithium hydroxide. The mean size of the spherical cathode powder was 1.1 μm. The discharge capacity of the Li(Ni_1/3Co_1/3Mn_1/3)O₂ powders with spherical shape and filled morphology was 195 mA h g⁻¹ at a current density of 0.1 C. The discharge capacities of the cathode powders with spherical shape and filled morphology at 55 °C decreased from 183 to 154 mA h g⁻¹ by the 30th cycle at a current density of 0.5 C.     

Multiferroic ceramics in BaO–Y2O3–Fe2O3–Nb2O5 system

Multiferroic ceramics in BaO–Y₂O₃–Fe₂O₃–Nb₂O₅ system were synthesized and their dielectric, ferroelectric and magnetic properties were evaluated. XRD results showed that the ceramic composite consists of a major phase of tetragonal tungsten bronze structured Ba₂YFeNb₄O₁₅, and minor phases of monoclinic YNbO₄ and hexagonal Ba₃Fe₂Nb₆O₂₁. Three dielectric relaxations were observed in the temperature range from 125 to 575 K. The relaxor dielectric behavior in the temperature range from 125 to 350 K was attributed to the random occupation of Fe³⁺ and Nb⁵⁺ ions at B site of the tungsten bronze structure. The electrode polarization and the inhomogeneous structure contributed to the high-temperature and middle-temperature dielectric relaxations, respectively. Both the ferroelectric hysteresis loop and the magnetic hysteresis loop were measured, which suggested that the synthesized ceramic composite was a promising candidate of multiferroics.     

Phase transition and piezoelectric properties of lead-free (Bi1/2Na1/2)TiO3–BaTiO3 ceramics

(1−x)(Bi_0.5Na_0.5)TiO₃–xBaTiO₃ ceramics (x=0.03, 0.06, 0.08, 0.12, 0.15, 0.20, 0.30, 0.40, 0.50, 0.60, 0.70, 0.80, and 0.90) were fabricated by a conventional solid-state reaction and their phase transitions and piezoelectric properties were investigated using XRD analyses, Curie temperature, the frequency dependance of dielectric constant, and P–E curves. A complete solid solution with a perovskite structure was formed in the whole composition range of BNT–BT and more than two phase transitions arising from a compositional change were found. With increasing BaTiO₃ content, the sequence of phase transitions from a rhombohedral structure to unknown tetragonal structures and finally a tetragonal structure with the space group P4mm has been established. While the rhombohedral–tetragonal phase transition led to superior piezoelectric properties in BNT–BT ceramics, other phase transitions between tetragonal structures had a little effect on piezoelectric properties. The d₃₃, ε_r, k_p, k_t, and Q_m and values lied in ranges of 40–130 pC/N, 400–900, 10–30%, 15–30%, and 50–250, respectively.     

O1/A1/O2/A2工艺处理焦化废水试验研究

通过对短程硝化反硝化工艺的研究,开发了好氧/厌氧/好氧/缺氧(O1/A1/O2/A2)生物脱氮新工艺并用于焦化废水的处理。考察了NH4+-N、COD、TN对反应器运行效果影响。结果表明,当进水COD平均为3 012.9 mg/L,NH4+-N、TN、挥发酚、总氰平均质量浓度分别为590.5、608.4、361.8、34.5 mg/L;出水COD平均为81.7 mg/L,出水NH4+-N、TN、挥发酚、总氰的平均质量浓度分别为0.1、9.9、0.1、0.1 mg/L,出水指标达到国家污水综合排放一级标准,A/O工艺处理这种焦化废水TN偏高,而用O1/A1/O2/A2工艺可以解决这一问题,实现了TN脱除。考察了温度、DO、pH对短程硝化影响。结果表明,在DO质量浓度为1.0～1.5 mg/L、温度在30～35℃、pH 7.5～8.0,系统能够进行稳定短程硝化反硝化。     

结构优化的异质Ca(Mg1/3Ta2/3)O3/CaTiO3薄膜介电性能

采用Pechini方法,在Pt/Ti/SiO₂/Si(100)基板上沉积了均质Ca(Mg1/3Ta2/3)O3 (CMT),CaTiO₃(CT)和堆叠次序不同以及摩尔比不同的异质Ca(Mg_1/3Ta_2/3)O₃/CaTiO₃(CMT/CT)薄膜。结果表明:以CT为底层的异质CMT/CT薄膜可以形成单一的钙钛矿结构,以CMT为底层的异质薄膜则有杂相产生。对于以CT为底层的不同摩尔比的异质CMT/CT薄膜,随着CMT含量的增加,异质薄膜中CT的衍射峰逐渐减小至消失,而CMT的结晶度变得更强,这说明以CT为缓冲层将有助于上层的CMT形成钙钛矿相。介电性能研究表明:异质CMT/CT薄膜的介电常数高度依赖于CMT的含量,而介电损耗不但与CMT含量有关,还与异质薄膜中界面数有关。当n(CMT):n(CT)=1:1 (摩尔比)时,异质的CMT/CT薄膜的介电常数和损耗分别为56和0.038。     

Magnetic properties of hard (CoFe2O4)–soft (Fe3O4) composite ceramics

Composite ceramics of CoFe₂O₄/Fe₃O₄ with different weight ratios were synthesized by Spark Plasma Sintering (SPS) at a sintering temperature of 500 °C. The X-ray diffraction patterns demonstrate that all samples are composed of CoFe₂O₄ and Fe₃O₄ phases. The magnetization curves for all the composite ceramic are single-step loops indicating the existence of exchange spring effect. Due to the competition between the exchange interaction and the dipolar interaction, magnetic properties like coercivity (H_c) and remanence (M_r) are sensitive to the weight ratio of the soft phase.     

O1/A/O2工艺处理高浓度焦化废水

焦化废水水质复杂,处理难点在于去除水中高浓度的CODCr、NH3-N和氰化物等。首钢某焦化厂废水处理工程采用以O1/A/O2工艺(预曝气/缺氧/好氧)为核心、前置除油预处理、后置混凝沉淀深度处理工艺,取得了较好的处理效果。运行结果表明:O1/A/O2工艺对CODCr和NH3-N的去除率分别可达95%和89%以上;混凝沉淀采用聚合硫酸铁絮凝剂和PAM助凝剂,加药量分别为600~800 mg/L和1~2 mg/L时,CODCr去除率在50%左右,脱色效果好。经过预处理、生化处理及深度处理后,出水主要污染物指标达到了《污水综合排放标准》的二级排放标准要求。     

Structural and magnetic properties of Li2O–Fe2O3 ceramic nanostructures

xLi₂O–(1−x)α-Fe₂O₃ (x=0.1, 0.3, 0.5, and 0.7) nanoparticle systems were successfully synthesized by mechanochemical activation of Li₂O and α-Fe₂O₃ mixtures for 0–12 h of ball milling time. The study aims at exploring the formation of magnetic oxide semiconductors at the nanoscale, which is of crucial importance for catalysis, sensing and electrochemical applications. X-ray powder diffraction (XRD), Mössbauer spectroscopy and magnetic measurements were used to study the phase evolution of xLi₂O–(1−x)α-Fe₂O₃ nanoparticle systems under the mechanochemical activation process. Rietveld refinement of the XRD patterns yielded the values of the particle size as function of composition and milling times and indicated the presence of Li-substituted hematite and tetra lithium iron oxide LiFeO₂, along with the formation of multiple phases for large x values and long milling times. The Mössbauer studies showed that the spectrum of the mechanochemically activated composites evolved from a sextet for hematite to sextets and a doublet upon duration of the milling process with lithium oxide. Magnetic measurements recorded at 5 K to room temperature (RT) in an applied magnetic field of 50,000 Oe showed that the magnetization of the milled samples is larger at low temperatures than at RT and increases with decreasing particle size. Zero field cooling measurements made possible the determination of the blocking temperatures of the specimens as function of ball milling time and evidenced the occurrence of superparamagnetism in the studied samples. This result correlates well with the observed presence of a quadrupole-split doublet in the Mössbauer spectra.     

Dielectric and piezoelectric properties of Pb(Sc1/2Nb1/2)O3–Pb(Ni1/3Nb2/3)O3–PbTiO3 ternary ceramic materials

The dielectric and electrical properties of xPb(Sc_1/2Nb_1/2)O₃–yPb(Ni_1/3Nb_2/3)O₃–zPbTiO₃ (PSNNT 100x/100y/100z) ternary ceramic materials near the morphotropic phase boundary (MPB) were investigated. The MPB follows on almost linear region between PSNNT 58/00/42 and PSNNT 00/68/32 of the binary systems. The maximum electromechanical coupling factor kp=70·7% was found at PSNNT 36/26/38, where ε₃₃^T/ε₀=3019 and Tc=210°C were obtained. These values are similar to those of the Pb(Sc_1/2Nb_1/2)O₃–Pb(Mg_1/3Nb_2/3)O₃–PbTiO₃ system and better than those of PZT.     

Densification behavior and electrical properties of CuO-doped Pb(In1/2Nb1/2)O3–Pb(Mg1/3Nb2/3)O3–PbTiO3 ternary ceramics

CuO modified Pb(In_1/2Nb_1/2)O₃–Pb(Mg_1/3Nb_2/3)O₃–PbTiO₃ (PIN–PMN–PT) ternary relaxor based ferroelectrics with the composition near the morphotropic phase boundary were synthesized by two-step columbite precursor method. The introduction of CuO significantly improved the sinterability of PIN–PMN–PT ceramics, resulting in the full densification of samples at lower sintering temperatures. It also profoundly modified the crystal structure and fracture mode of the ceramics. Properly increasing CuO content led to the disappearance of rhombohedral-tetragonal phase transition, remarkably improved the Curie temperature (T_c), and made the ceramics more relaxorlike. The ternary ceramics doped with 0.25 wt% CuO possessed optimum piezoelectric properties (d₃₃=584 pC/N, d₃₃^*=948 pC/N, and k_p=0.68), high ferroelectric properties (E_c=9.9 kV/cm, and P_r=33.1 μC/cm²), low dielectric loss (tan δ=0.9%), and wider temperature usage range (T_c=225 °C). The obtained properties are much higher than those of previously reported PIN–PMN–PT based ceramics, indicating that CuO doped PIN–PMN–PT is a promising candidate for electromechanical applications with high performance and wide temperature/electric field usage ranges.     

Structural and electrical properties of (Bi0.9Dy0.1)(Fe0.975TM0.025)O3±δ (TM=Ni,Cr and Ti) thin films

Pure BiFeO₃ and rare earth and transition metal ions co-doped (Bi_0.9Dy_0.1)(Fe_0.975TM_0.025)O_3±δ (TM=Ni²⁺, Cr³⁺ and Ti⁴⁺) thin films were prepared on Pt(111)/Ti/SiO₂/Si(100) substrates by using a chemical solution deposition method. The changes in the microstructure and the electrical properties with doping elements were investigated. The thin films were well crystallized and randomly oriented, with no detectable impurity and secondary phases. The leakage current densities were reduced and the ferroelectric properties were improved in the co-doped thin films. Among the thin films, the (Bi_0.9Dy_0.1)(Fe_0.975Cr_0.025)O₃ thin film exhibited well saturated hysteresis loops with remnant polarization (2P_r) of 36 μC/cm² and coercive electric field (2E_c) of 954 kV/cm at 1000 kV/cm and low leakage current density of 1.91×10⁻⁵ A/cm² at 100 kV/cm. The enhanced properties observed in the co-doped thin films could be considered as being the result of the suppression of oxygen vacancies and of the modified microstructure.     

稀土离子掺杂0.6BaTiO3-0.4Bi(Mg1/2Ti1/2)O3陶瓷的储能性能研究

弛豫铁电陶瓷由于优异的介电和储能性能，在陶瓷储能电容器中具有较大的应用潜力。本文采用固相烧结法制备了0.05 mol Nd³⁺、Sm³⁺和Gd³⁺稀土离子掺杂的0.6BaTiO₃-0.4Bi(Mg_1/2Ti_1/2)O₃陶瓷。结果表明，所有陶瓷均表现为典型的弛豫铁电体，其中Nd³⁺掺杂的陶瓷样品具有最小的介电损耗，获得了最大的击穿场强(350 kV/cm)和储能效率(94.38%);Gd³⁺掺杂的陶瓷样品具有最大的介电常数，获得了最高的可恢复储能密度(4.33 J/cm³)。     

Piezoelectric and dielectric properties of (Bi0.5Na0.5)0.94Ba0.06TiO3–Ba(Zr0.04Ti0.96)O3 lead-free piezoelectric ceramics

Lead-free piezoelectric ceramics of (1 − x)(Bi_0.5Na_0.5)_0.94Ba_0.06TiO₃–xBa(Zr_0.04Ti_0.96)O₃ (abbreviated as BNBT–BZT100x, wherein x from 0 to 10 mol%) were fabricated. We have studied effects of amount of BZT content on the electrical properties and microstructures. X-ray diffraction analysis indicates that a solid solution is formed when BZT diffuses into the BNBT lattice, and further the crystal structure of sintered hybrid changes from rhombohedral to tetragonal symmetry along with increasing BZT content. Piezoelectric property measurements reveal that the BNBT–BZT4 ceramics has the highest piezoelectric performance, for example, the piezoelectric constant d₃₃ reaches to 167 pC/N and planar electromechanical coupling factor k_p is up to 0.27. In addition, the effect of Bi₂O₃ on the electrical properties and microstructure of the BNBT–BZT4 ceramics have also been studied, and found that the doping of Bi enhances the piezoelectric properties of ceramics.