Sm的氧化对Sm2(Co,Fe,Cu,Zr)17磁体微观结构及磁性能的影响

用粉末冶金法制备了Sm2(Co,Fe,Cu,Zr)17磁体,研究了工艺过程Sm的氧化对材料性能影响。微观分析表明,Sm的氧化主要以Sm2O3形成析出孔洞,破坏了材料的组织结构,从而影响材料的性能。     

氧空位对氧化锆相结构稳定性及相变过程的影响

从晶体学和配位学的角度，结合电化学技术，讨论了氧空位对氧化锆相结构结构稳定性的影响及氧化锆四方相单斜相转变过程中的作用。结果表明：氧空位的存在与变化不仅影响着氧化锆相结构的稳定性，而且影响着氧化锆的低温相变过程。对于含有一定担氧空位的亚稳四方相氧化锆，氧空位浓度的增加与减少都会进一步降低其结构稳定性，使之更加容晚地向单斜相转变     

“Dark hole” cure in Ba4.2Nd9.2Ti18O54 microwave dielectric ceramics

Large size Ba_4.2Nd_9.2Ti₁₈O₅₄ (BNT) ceramics doped with MnCO₃, CuO and CoO were prepared by the conventional solid-state method. Only a single BaNd₂Ti₄O₁₂ phase was formed in all samples. No second phase was found in the XRD patterns. The bulk density increases slightly because of the dopants. The SEM results showed that the grain size of Mn²⁺and Cu²⁺-doped BNT ceramics became larger with the increasing amount of dopants. The permittivity of all samples stays the same. However, the Q×f value of BNT ceramics increases by doping, especially with Mn²⁺ ions. The conductivity of BNT ceramic doped with Mn²⁺(0.5 mol‰) under high temperature is lower than that without doping. There are fewer defects in Mn²⁺-doped BNT ceramics. The XPS results indicated that Ti reduction was suppressed in BNT ceramics doped with 0.5 mol‰ Mn²⁺. BNT ceramics doped with 0.5 mol‰ Mn²⁺ ions sintered at 1320 °C for 2 h exhibited good microwave dielectric properties, with ε_r=88.67, Q×f=7408 GHz and τf = 82.98 ppm/°C.     

Double polarization hysteresis and dramatic influence of small compositional variations on the electrical properties in Bi4Ti3O12 ceramics

This work reports the existence of double polarization hysteresis (P–E) loop in Aurivillius-phase ferroelectric Bi₄Ti₃O₁₂ (BiT) and reveals dramatic influence of small compositional variations on the electrical properties of it. The double polarization hysteresis is a characteristic of the interaction of defects with domain walls. This characteristic becomes more pronounced in Bi-deficient and Mg-doped BiT due to an increase in oxygen vacancy concentration at the lattices. Normal and saturated P–E loop is recalled by Nb donor doping, and associated composition Bi₄Ti_2.97Nb_0.03O_12.015 (BiT-0.03Nb) shows high remnant polarization (P_r = 12.5 μC/cm²) and large field-induced strain (S₃₃ = 5.6 × 10^?4). In addition, this doping results in bulk conductivity (σ_b) of BiT decreasing dramatically and associated activity energy (E_a) increasing significantly. In contrast, high oxide ion conductivity is induced with Mg²⁺ acceptor doping, and at 600 °C the optimum composition has ionic conductivity of ?0.65 × 10^?2 S cm^?1 in the bulk.     

Enhanced piezoelectric properties and temperature stability of Bi4Ti3O12-based Aurivillius ceramics via W/Nb substitution

Bi₄Ti₃O₁₂ (BIT), a typical Aurivillius ceramics with high Curie temperature (T_c ? 675 °C), has great potential for high temperature applications. This work provides an effective method of inducing structure distortion, relieving the tetragonal strain of the TiO₆ octahedron and decreasing the concentration of oxygen vacancies to improve the piezoelectricity and temperature stability of BIT ceramics. Bi₄Ti_2.98W_0.01Nb_0.01O₁₂ possesses an optimum piezoelectric coefficient (d₃₃) of 32 pC/N, a high T_c of 655 °C and a large resistivity of 3 × 10⁶ Ω·cm at 500 °C. The maximum d₃₃ reported here is approximately quadruple than that of pure BIT (?7 pC/N). Moreover, the d₃₃ of W/Nb co-doped BIT and the in-situ temperature stability of the compression-mode sensor present a highly stable characteristic in the range of 25–600 °C. These results imply that W/Nb-modified BIT ceramics is a promising candidate for application at high temperatures of up to 600 °C.     

Polymorphic phase transition in BaTiO3 by Ni doping

We demonstrate a phase transition between BaTiO₃ polymorphs induced by Ni substitution experimentally. The structural evolution of tetragonal-to-hexagonal polymorph in Ni-doped BaTiO₃ ceramics is observed macroscopically and then, visualized in an atomic scale. Under this structural transition, the long-range ferroelectric ordering in the undoped BaTiO₃ with tetragonal symmetry is suppressed and eventually, vanishes in the heavily Ni-doped BaTiO₃ with hexagonal symmetry and dielectricity. An oxygen vacancy defect can be created at a local Ni doping site with a decrease in the charge valence state from Ti⁴⁺ (3d⁰) to Ti³⁺ (3d¹). With the reduction of the Ti⁴⁺ oxidation state, the polar Ti–O ionic displacement is degenerated in the tetragonal BaTiO₃ and thereby, the short-range Coulomb repulsion may be restored in the hexagonal BaTiO₃ resulting in a polymorphic phase transition. Our work is of potential interest for artificial realization of an exotic phase in complex oxide materials by doping.     

Effect of lanthanum content on the conduction behaviors and relaxation processes of lead lanthanum zirconate titanate antiferroelectric ceramics

(Pb_1-xLa_x) (Zr_0.92Ti_0.08)_1-x/4O₃ (PLZT x/92/8, x = 3, 5 and 7 at%) ceramics with compositions near the antiferroelectric (AFE)-ferroelectric (FE) phase boundary were fabricated by a solid-state reaction method. The effect of lanthanum content on the conduction behaviors and relaxation processes has been investigated. It was verified that the main phase with orthorhombic structure was formed in all compositions. The increase of lanthanum substitution resulted in an enhancement of diffuse phase transition. Impedance analysis suggested that the ac conductivity decreased with increasing lanthanum content. Moreover, thermally stimulated depolarization current study was utilized to establish the correlation between defect structures and relaxation processes. It showed three peaks with distinct characteristics, which originated from dipole orientation, oxygen vacancy migration and phase transition respectively. The oxygen vacancy-related defects induced by lanthanum doping were mainly responsible for the variation of conduction behaviors and relaxation processes.     

Electrochemical Performance of PrBaCo2O5+δ and Sm0.5Sr0.5CoO3−δ Infiltrated Ce0.9Gd0.1O1.95 Cathodes

Cathodes with PrBaCo₂O_5+δ (PBC) and Sm_0.5Sr_0.5CoO_3−δ (SSC) infiltrated on Ce_0.9Gd_0.1O_1.95 (CGO) backbones are prepared using metal nitrates as precursors and ethanol as wetting agent. Electrochemical impedance spectra (EIS) are measured from cathode/CGO/cathode symmetrical cells in 400–650 °C under humidified air. The results indicate that interfacial area specific resistance (ASR) value decreases and then increases with infiltrate loading and minimum values occur at 50 wt.% loading (relative to sum of infiltrate and backbone) for both PBC and SSC infiltrates. ASR values of PBC infiltrated cathodes are lower than that of corresponding SSC infiltrated cathodes in general, and in particular ASR values as low as 1.36 × 10⁻² and 2.27 × 10⁻² Ω cm² are obtained at 650 °C in air for 50 wt.% PBC and 50 wt.% SSC infiltrated cathodes, respectively. Conductivity values of CGO electrolyte increase with infiltrate loading and agree with the reported values when the loading reaches 50 wt.%.     

商品建筑供求关系研究

近年来,商品建筑供求失衡的局面比较严重,房室空置率很高的现象是可行性论证失误造成的。为此,分析了商品建筑可行性论证失误的原因,探讨了对商品建筑需求总量的错误认识,研究了商品建筑供给、需求及相互间关系,构建了商品建筑供求平衡数学表达式,提出了我国商品建筑空置率的参考指标,对商品建筑供求关系的研究有利于提高投资的准确性,保证商品建筑开发数量应遵循商品建筑经济的基本规律。     

Sm2Co17稀土永磁材料的研究概况

随着现代工业的发展,对永磁体的要求也越来越高,既要求磁性能优良,又要求稳定性好,可靠性高.目前,对Sm2Co17稀土永磁材料的研究主要体现在高温永磁体、高稳定性永磁体和成型工艺等方面.影响Sm2Co17磁体性能的因素较多,其中比较重要的因素是磁体的显微组织、时效处理及合金的化学成分等.