Synergistic effects of intrinsic cation disorder and electron-deficient substitution on ion and electron conductivity in La1-xSrxCo0.5Mn0.5O3-δ (x = 0, 0.5, and 0.75).

The effects of intrinsic cation disorder and electron-deficient substitution for La1-xSrxCo0.5Mn0.5O3-δ (LSCM, x = 0, 0.5, and 0.75) on oxygen vacancy formation, and their influence on the electrochemical properties, were revealed through a combination of computer simulation and experimental study. First-principles calculations were first performed and found that the tendency of the oxygen vacancy formation energy was Mn(3+)-O*-Mn(4+) < Co(2+)-O*-Co(3+) < Co(2+)-O*-Mn(4+), meaning that antisite defects not only facilitate the formation of oxygen vacancy but introduce the mixed-valent transition-metal pairs for high electrical conductivity. Detailed partial density of states (PDOS) analysis for Mn on Co sites (MnCo) and Co on Mn sites (CoMn) indicate that Co(2+) is prone to being Co(3+) while Mn(4+) is prone to being Mn(3+) when they are on antisites, respectively. Also it was found that the holes introduced by Sr tend to enter the Co sublattice for x = 0.5 and then the O sublattice when x = 0.75, which further promotes oxygen vacancy formation, and these results are confirmed by both the calculated PDOS results and charge-density difference. On the basis of microscopic predictions, we intentionally synthesized a series of pure LSCM compounds and carried out comprehensive characterization. The crystal structures and their stability were characterized via powder X-ray Rietveld refinements and in situ high-temperature X-ray diffraction. X-ray photoelectron spectroscopy testified to the mixed oxidation states of Co(2+)/Co(3+) and Mn(3+)/Mn(4+). The thermal expansion coefficients were found to match the Ce0.8Sm0.2O2-δ electrolyte well. The electrical conductivities were about 41.4, 140.5, and 204.2 S cm(-1) at doping levels of x = 0, 0.5, and 0.75, and the corresponding impedances were 0.041, 0.027, and 0.022 Ω cm(2) at 850 °C, respectively. All of the measured results testify that Sr-doped LaCo0.5Mn0.5O3 compounds are promising cathode materials for intermediate-temperature solid oxide fuel cells.

Heterointerface Effect in Accelerating the Cathodic Oxygen Reduction for Intermediate-Temperature Solid Oxide Fuel Cells.

A solid-state mixing method was adopted to prepare a new Pr0.8Sr0.2Fe0.7Ni0.3O3-δ-Pr1.2Sr0.8Fe0.4Ni0.6O4+δ (PSFN113-214) composite cathode oxide for the solid oxide fuel cells (SOFCs). Herein, heterointerface engineering was investigated for the performance enhancement. It was found that the oxygen vacancy content could be increased by mixing the PSFN214 with PSFN113, which gave rise to the formation of a heterostructure, and resulted in the promotion of oxygen ion transport as well as the specific surface area. The optimum mixing ratio 5:5 resulted in the highest oxygen vacancy content and the largest specific surface area, indicating the strongest interface effect. Polarization resistance of PSFN113-214 (5:5) was 0.029 Ω cm2 at 800°C, which was merely 24% of PSFN113 and 39% of PSFN214. The corresponding maximum power density was 0.699 W cm-2, which was nearly 1.44 times of PSFN113 and 1.24 times of PSFN214. Furthermore, the voltage attenuation rate after 100 h was merely 0.0352% h-1. Therefore, the new PSFN113-214 composite could be a prospective cathode oxide for SOFCs.

Effect of MgO and Fe2O3 dual sintering aids on the microstructure and electrochemical performance of the solid state Gd0.2Ce0.8O2-δ electrolyte in intermediate-temperature solid oxide fuel cells.

Solid state electrolytes have been intensively studied in the solid oxide fuel cells (SOFCs). The aim of this work is to investigate the effects of MgO and Fe2O3 dual sintering aids on the microstructure and electrochemical properties of solid state Gd0.2Ce0.8O2-δ (GDC) electrolytes, which are prepared by a sol-gel method with MgO and Fe2O3 addition to the GDC system. It is found that the addition of MgO and Fe2O3 can reduce the sintering temperature, increase densification and decrease the grain boundary resistance of the electrolyte. The 2 mol% MgO and 2 mol% Fe2O3 co-doped GDC (GDC-MF) exhibits the highest grain boundary conductivity. At 400°C, the grain boundary conductivity and total conductivity of GDC-MF are 15.89 times and 5.56 times higher than those of GDC. The oxygen reduction reaction (ORR) rate at the electrolyte/cathode interface of GDC-MF is 47 % higher than that of GDC. Furthermore, the peak power density of a single cell supported by GDC-MF is 0.45 W cm-2 at 700°C, 36.7% higher than that of GDC. Therefore, the GDC-MF should be a promising electrolyte material for intermediate-temperature solid oxide fuel cells (IT-SOFCs).

Electronic and magnetic properties of the monoclinic phase BiCrO(3) from first-principles studies.

Based on density functional theory, we systematically studied the electronic and magnetic properties of the real experimental structural phase BiCrO(3) with the space group C 2/c. It is found that the ground state is a moderately correlated Mott-Hubbard insulator with G-type antiferromagnetic structure, which is in agreement with the experimental observations. The magnetism can be qualitatively understood in terms of the superexchange mechanism via Cr1(t(2g))-O 2p-Cr2(t(2g)). Moreover, the total energies calculated for various magnetic orderings lead to an estimate of the magnetic interaction constants.

Semi-Interpenetrating Polymer Networks Based on Cyanate Ester and Highly Soluble Thermoplastic Polyimide.

Thermoplastic polyimide (TPI) was synthesized via a traditional one-step method using 2,3,3',4'-biphenyltetracarboxylic dianhydride (3,4'-BPDA), 4,4'-oxydianiline (4,4'-ODA), and 2,2'-bis(trifluoromethyl)benzidine (TFMB) as the monomers. A series of semi-interpenetrating polymer networks (semi-IPNs) were produced by dissolving TPI in bisphenol A dicyanate (BADCy), followed by curing at elevated temperatures. The curing reactions of BADCy were accelerated by TPI in the blends, reflected by lower curing temperatures and shorter gelation time determined by differential scanning calorimetry (DSC) and rheological measurements. As evidenced by scanning electron microscopy (SEM) images, phase separation occurred and continuous TPI phases were formed in semi-IPNs with a TPI content of 15% and 20%. The properties of semi-IPNs were systematically investigated according to their glass transition temperatures (Tg), thermo-oxidative stability, and dielectric and mechanical properties. The results revealed that these semi-IPNs possessed improved mechanical and dielectric properties compared with pure polycyanurate. Notably, the impact strength of semi-IPNs was 47%-320% greater than that of polycyanurate. Meanwhile, semi-IPNs maintained comparable or even slightly higher thermal resistance in comparison with polycyanurate. The favorable processability and material properties make TPI/BADCy blends promising matrix resins for high-performance composites and adhesives.

Effects and mechanisms of electroacupuncture at PC6 on frequency of transient lower esophageal sphincter relaxation in cats.

AIM: To investigate the effects of electroacupuncture (EA) at neiguan (PC6) on gastric distention-induced transient lower esophageal sphincter relaxations (TLESRs) and discuss the mechanisms of this treatment. METHODS: Protocol I: Twelve healthy cats underwent gastric distention for 60 min on the first day. Electrical acupoint stimulation was applied at the neiguan or a sham point on the hip in randomized order before gastric distention, on the third day and fifth day. Those cats that underwent EA at neiguan on the fifth day were named "Neiguan Group" and the cats that underwent EA at a sham acupoint on the fifth day were named "Sham Group" (control group). During the experiment the frequency of TLESRs and lower esophageal sphincter (LES) pressure were observed by a perfused sleeve assembly. Plasma levels of gastrin (GAS) and motilin (MTL) were determined by radioimmunoassay. Nitrite/nitrate concentration in plasma and tissues were measured by Griess reagent. The nuclei in the brain stem were observed by immunohistochemistry method of c-Fos and NADPH-d dyeing. Protocol II: Thirty six healthy cats were divided into 6 groups randomly. We gave saline (2 mL iv. control group), phaclofen (5 mg/kg iv. GABA-B antagonist), cholecystokinin octapeptide (CCK-8) (1 microg/kg per hour iv.), L-Arginine (200 mg/kg iv.), naloxone (2.5 micromol/kg iv.) and tacrine (5.6 mg/kg ip. cholinesterase inhibitor) respectively before EA at Neiguan and gastric distention. And the frequencies of TLESRs in experimental groups were compared with the control group. RESULTS: Protocol I: Not only the frequency of gastric distention-induced TLESR in 60 min but also the rate of common cavity during TLESRs were significantly decreased by EA at neiguan compared to that of sham acupoint stimulation. C-Fos immunoreactivity and NOS reactivity in the solitarius (NTS) and dorsal motor nucleus of the vagus (DMV) were significantly decreased by EA at neiguan compared to that of the sham group. However, the positive nuclei of C-Fos and NOS in reticular formation of the medulla (RFM) were increased by EA at neiguan. Protocol II: The inhibited effect of EA at neiguan on TLESR's frequency was completely restored by pretreatment with CCK (23.5/h vs 4.5/h, P < 0.05), L-arginine (17.5/h vs 4.5/h, P < 0.05) and naloxone(12/h vs 4.5/h, P < 0.05). On the contrary, phaclofen (6/h vs 4.5/h, P > 0.05) and tacrine (9.5/h vs 4.5/h, P > 0.05) did not influence it. CONCLUSION: Electric acupoint stimulation at Neiguan significantly inhibits the frequency of TLESR and the rate of common cavity during TLESR in cats. This effect appears to act on the brain stem, and may be mediated through nitric oxide (NO), CCK-A receptor and mu-opioid receptors. But the GABAB receptor and acetylcholine may not be involved in it.

Mn valence, magnetic, and electrical properties of LaMnO3+δ nanofibers by electrospinning.

LaMnO3+δ nanofibers have been prepared by electrospinning. The nearly 70% of Mn atoms is Mn4+, which is much higher than that in the nanoparticles. The average grain size of our fibers is approximately 20 nm, which is the critical size producing the nanoscale effect. The nanofibers exhibit a very broad magnetic transition with Tc≈255 K, and the Tc onset is around 310 K. The blocking temperature TB is 180 K. The sample shows weak ferromagnetic property above the TB and below Tc and superparamagnetic property near the Tc onset. The resistivity measurements show a metal-insulator transition near 210 K and an upturn at about 45 K.

Charge, orbital, and magnetic ordering in YBaFe2O5 from first-principles calculations.

First principles calculations using the augmented plane wave plus local orbitals method, as implemented in the WIEN2k code, have been used to investigate the electronic and magnetic properties of YBaFe2O5, especially as regards the charge-orbital ordering. Although the total 3d charge disproportion is rather small, an orbital order parameter defined as the difference between t2g orbital occupations of Fe2+ and Fe3+ cations is large (0.73) and gives unambiguous evidence for charge and orbital ordering. Strong hybridization between O2p and Fe e g states results in the nearly complete loss of the separation between the total charges at the Fe2+ and Fe3+ atoms. Furthermore, the relationship between the orbital ordering and charge ordering is also discussed. The dxz orbital ordering is responsible for the stability of the G-type antiferromagnetic spin ordering and the charge ordering pattern.

Magnetic structure and orbital ordering in tetragonal and monoclinic KCrF(3) from first-principles calculations.

KCrF(3) has been systematically investigated by using the full-potential linearized augmented plane wave plus local orbital method within the generalized gradient approximation and the local spin density approximation plus the on-site Coulomb repulsion approach. The total energies for ferromagnetic and three different antiferromagnetic configurations are calculated in the high-temperature tetragonal and low-temperature monoclinic phases, respectively. It reveals that the ground state is the A-type antiferromagnetic in both phases. Furthermore, the ground states of the two phases are found to be Mott-Hubbard insulators with the G-type orbital ordering pattern. In addition, our calculations show the staggered orbital ordering of the 3d(x(2) ) and 3d(y(2) ) orbitals for the tetragonal phase and the 3d(z(2) ) and 3d(x(2) ) orbitals for the monoclinic phase, which is in agreement with the available data. More importantly, the relationship between magnetic structure and orbital ordering as well as the origin of the orbital ordering are analyzed in detail.