Phase transition, structural and electrical properties of Pb(Zn1/3Nb2/3)O3-doped Pb(Ni1/3Nb2/3)O3-PbTiO3 ceramics prepared by solid-state reaction method

Phase pure perovskite (1−x−y)Pb(Ni_1/3Nb_2/3)O₃-xPb(Zn_1/3Nb_2/3)O₃-yPbTiO₃ (PNN-PZN-PT) ferroelectric ceramics were prepared by conventional solid-state reaction method via a B-site oxide mixing route. The PNN-PZN-PT ceramics sintered at the optimized condition of 1185 °C for 2 h exhibit high relative density and rather homogenous microstructure. With the increase of PbTiO₃ (PT) content, crystal structure and electrical properties of the synthesized PNN-PZN-PT ceramics exhibit successive phase transformation. A morphotropic phase boundary (MPB) is supposed to form in (0.9−x)PNN-0.1PZN-xPT at a region of x=32-36 mol% confirmed by X-ray diffraction (XRD) measurement and dielectric measurement. The MPB composition can be pictured as providing a “bridge” connecting rhombohedral ferroelectric (FE) phase and tetragonal one since crystal structure of the MPB composition is similar to both the rhombohedral and tetragonal lattices. Dielectric response of the sintered PNN-PZN-PT ceramics also exhibits successive phase-transition character. 0.64PNN-0.1PZN-0.26PT exhibits broad, diffused and frequency dependent dielectric peaks indicating a character of diffused FE-paraelectric (PE) phase transition of relaxor ferroelectrics and 0.40PNN-0.1PZN-0.50PT exhibits narrow, sharp and frequency independent dielectric peaks indicating a character of first-order FE-PE phase transition of normal ferroelectrics. The FE-PE phase transition of 0.56PNN-0.1PZN-0.34PT is nearly first-order with some diffused character, which also exhibits the largest value of piezoelectric constant d₃₃ of 462pC/N.     

SiC crystal growth from transition metal silicide fluxes

SiC crystal growth in transition metal silicide melts was investigated by using spontaneous infiltration and solution methods. In the infiltration experiments, SiC powder preforms were infiltrated with Fe_xSi_y (Fe₃Si, Fe₅Si₃ and FeSi) and CoSi melts. The dissolution and precipitation of SiC led to SiC crystals growth in the infiltrated Fe₅Si₃ and CoSi melts, SiC particles coalescing in FeSi and free carbon precipitation in Fe₃Si. In the solution experiments, carbon from the graphite crucible dissolved in and reacted with FeSi₂ and Ti_2.3Si_7.7 to form SiC crystals. Scanning electron microscopy (SEM), X‐ray diffraction (XRD) and Raman scattering spectrometer were employed to investigate SiC crystals growth. Based on the investigation, the effect of solution content on the SiC crystal growth, the growth mechanisms in both methods and prototypes of the SiC crystals are also discussed. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

New lanostane-type triterpene acids from wolfiporia extensa

ABSTRACT: BACKGROUD: Dried sclerotia of Wolfiporia extensa (Polyporaceae) is used to invigorate the spleen and to tranquilize the mind in Chinese herbal medicine. Lanostane-type triterpene acids were regard as major secondary metabolites from dried sclerotia of W. extensa. RESULTS: Three new lanostane-type triterpene acids, 3-epi-benzoyloxyl-dehydrotumulosic acid (1), 3-epi-(3'-O-methyl malonyloxy)-dehydrotumulosic acid (2) and 3-epi-(3'-hydroxy-3'-methylglutaryloxyl)-dehydrotumulosic acid (3), were isolated from the sclerotia of W. extensa, together with 3 known lanostane derivatives (4-6). Their structures were elucidated on the basis of spectroscopic analysis, including 1D and 2D-NMR techniques. CONCLUSION: Six lanostane derivatives including three new triterpene acids and three known compounds were reported from the sclerotia of W. extensa in this paper.     

Determination of mercury(II) traces in drinking water by inhibition of an urease reactor in a flow injection analysis (FIA) system

 The integration of an urease reactor into a gas diffusion flow injection system was investigated for the determination of urease inhibitors. The enzyme was immobilized by entrapping in polyacrylamide gel. Besides copper and silver ions mercury ions inhibit the conversion of urea to carbon dioxide and ammonia catalysed by urease. The pH change of the carrier solution caused by the ammonia released was measured potentiometrically with a pH electrode. The inhibition behaviour of Hg(II) ions was investigated. A linear range from 2 to 20 μg L^-1 Hg(II) was obtained after a 90 s inhibition, with a correlation coefficient of r=0.9997. The relative standard deviation was 1.4% for five measurements of 2 μg L^-1Hg(II). A sample frequency of 7 h^-1 was achieved. The inhibited enzyme can be reactivated. The method was applied to the determination of Hg(II) in two drinking water samples. Received: 16 April 1996/Revised: 3 June 1996/Accepted: 11 June 1996     

Dielectric,electromechanical coupling properties of Mn-doped Na0.5Bi0.5TiO3–BaTiO3 lead-free single crystal

Applied Physics A - Mn-doped 0.948Na0.5Bi0.5TiO3–0.052BaTiO3 (NBBT94.8/5.2) lead-free single crystal with excellent piezoelectric and electromechanical coupling properties was successfully...     

Two New Monoterpenes from Mentha haplocalyx Briq.

Two new monoterpenes with a skeleton similar to the 1,8‐cineole skeleton, i.e., (1R,4R)‐3,3,5‐trimethyl‐2‐oxabicyclo[2.2.2]oct‐5‐en‐4‐ol ( 1 ) and (1R,4R)‐4‐methoxy‐3,3,5‐trimethyl‐2‐oxabicyclo[2.2.2]oct‐5‐ene ( 2 ), were isolated from an aqueous acetone extract of the aerial parts of Mentha haplocalyx, together with three known compounds. Their structures were elucidated by extensive spectroscopic methods and by comparison with reference values.     

Absorbable phenylpropenoyl sucroses from Polygala tenuifolia

Three phenylpropenoyl sucroses--sibiricose A5, A6 and 3',6-disinapoyl sucrose--were isolated from the 30% EtOH extract of Polygala tenuifolia, which displayed antidepressant-like action. HPLC analysis indicated that the three phenylpropenoyl sucroses could be absorbed into serum. From the serum pharmacochemistry point of view, these three phenylpropenoyl sucroses might prevent or relieve depression.     

修理设备可更换且修理工多重延误休假的单部件可修系统

假定部件的寿命、修理时间和修理工的休假时间均服从一般连续型分布.修理工的延误休假时间服从指数分布,并且修理设备的寿命服从爱尔朗分布,其更换时间服从一般连续型分布的情况下,研究了修理设备可更换且修理工可多重延误休假的单部件可修系统.通过使用补充变量法、广义马尔可夫过程方法和拉普拉斯变换工具,讨论了系统的瞬时可用度、稳态可用度以及(0,t]时间内系统的平均故障次数和稳态故障频度,得到了系统和修理设备主要可靠性指标的拉普拉斯变换表达式.     

微乳液介质中5′-硝基水杨基荧光酮光度法测定微量铅

研究了在阳离子型微乳液:CTMAB/n-C5H11OH-n-C7H16/H2O介质中,Pb(Ⅱ)-5′-硝基水杨基荧光酮(5′-NSF)的显色反应.在pH9.0NH3.H2O-NH4Cl缓冲体系中,Pb(Ⅱ)与5′-NSF形成1∶2紫色络合物,ε575=1.14×105L.mol-1.cm-1,Pb(Ⅱ)浓度在0～0.52mg/L范围内服从比尔定律.方法用于样品中微量铅的测定,结果令人满意.