Bi、Nb双施主掺杂对钛酸钡基陶瓷性能的影响

本文首次在钛酸钡中以BiCl3、NbCl5的溶液形式引入Bi、Nb元素,采用低温固态反应制备了Bi、Nb双施主掺杂的纳米BaTiO3基PTC陶瓷粉,同时研究了烧结条件对PTC陶瓷材料性能的影响。利用XRD和TEM分析了样品的物相及微观形貌,发现样品为立方晶系的完全互溶取代固溶体,颗粒基本呈球形,且分布比较均匀,粒径大约50～60 nm。制陶实验表明,以Bi、Nb进行双施主掺杂可有效改善材料的PTC性能,当最佳烧结温度为1 330℃、保温时间为20 min时,可以得到室温电阻为12.93Ω,升阻比为1.920×105的电性能优良的PTC陶瓷。     

稀土锰氧化物La0.7Ca0.3Mn1-xCuxO3低场磁电阻及电传输特性研究

采用溶胶-凝胶法制备了系列多晶CMR材料La0.7Ca0.3Mn1-xCuxO3（x=0%,1%,5%,10%,15%,20%）。在77-350 K温度范围内测量了样品的电阻率及磁电阻大小。实验结果发现：系列样品TC随掺杂量增加而递减;系列样品的电阻率峰及磁电阻峰在整个测温范围内随掺杂量的增加均依次被展宽直至消失,当掺杂量为x≥10%时,电阻率随温度的变化在整个测温范围内呈现绝缘相行为;同时还发现,掺杂量为x≥10%时,样品的磁电阻在整个测温区内基本表现为隧穿磁电阻。基于我们采用蒙特卡罗模拟方法提出的逾渗模型及隧穿磁电阻模型,对样品的磁电阻行为进行了很好的解释。对系列样品的ρ-T曲线进行lnρ-T^-（1/4）系拟合,发现掺杂量为x=10%样品在整个温区内的lnρ-T^-（1/4）系基本呈线性。     

Ti掺杂对(LaMn1-xTixO3)0.67(NiMn2O4)0.33(0≤x≤0.7)陶瓷材料微结构及电性能影响

采用氧化物固相法制备(LaMn1-xTixO3)0.67(NiMn2O4)0.33系列NTC(Negative temperature coefficient)复合热敏电阻材料。利用TG/DSC、激光粒度分析、XRD、SEM、阻-温特性和老化性能测试等手段,确定了粉体煅烧温度,表征了粉体的颗粒尺寸、陶瓷体的物相、形貌及其电学特性、稳定性等与Ti掺杂量的关系。结果表明:在1 200~1 300℃烧结温度范围内,(LaMn1-xTixO3)0.67(NiMn2O4)0.33复合体系的电阻率ρ25℃随Ti含量的增加而显著增加;电阻率ρ25℃和B值变化范围分别为4.4~53 179Ω.cm、1 357~3 998 K。125℃下老化1 000 h阻值变化率ΔR/R0均小于0.51%。该复合体系电阻率、B值调整范围较大,稳定性好,是一种具有实际应用价值的NTC热敏电阻材料。     

La0.7-xDyxSr0.3MnO3(0.00≤x≤0.70)的TCR研究

研究了La位Dy掺杂对La0.7-xDyxSr0.3MnO3(0.00≤x≤0.70)电阻温度系数(TCR)的影响.实验结果表明:Dy掺杂将引起电阻率曲线的急剧变化,导致出现大的TCR;随Dy掺杂的增加,TCR在x=0.30出现峰值,然后随掺杂量的增加逐步降低.体系出现大的TCR,来源于Dy掺杂引起的晶格畸变和额外磁性耦合.     

稀土气相扩渗BaTiO3基PTC陶瓷的NTCR效应

采用稀土气相扩渗法制备了La改性的BaTiO3基PTC陶瓷,并对其室温电阻率的变化及温-阻效应进行了研究.结果表明,BaTiO3基PTC陶瓷经La气相扩渗后,室温电阻率从2.7×109Ω.m下降到220Ω.m,在25-500℃范围内,电阻率随温度升高单调递减,从220Ω.m降至5.8Ω.m,产生了明显的NTCR效应.结合XRD,SEM,EDAX以及介电性能测试结果分析了La气相扩渗BaTiO3基PTC陶瓷NTCR效应的形成机理,建立了NTCR效应的物理结构模型.     

钙钛矿型稀土锰氧化物La_(0.7)Sr_(0.3)Fe_xMn_(1-x)O_3的磁性和巨磁电阻效应

采用溶胶 凝胶工艺制备了La0 .7Sr0 .3FexMn1 -xO3化合物 ,研究Fe掺杂对材料的导电性能、磁性能、磁电阻性能的影响。发现随Fe含量的增加 ,材料的电阻率提高 ,铁磁居里温度 (TC)下降 ,巨磁电阻效应增强。观察到x =0 0 5和x =0 0 8的样品的电阻率随温度变化曲线出现双峰。对于x =0 0 8的样品 ,在室温附近磁电阻达到 18% (8× 10 5 A·m- 1 外场 )。对于x >0 0 8的样品 ,金属 绝缘体转变温度均比相应的铁磁 顺磁转变温度低 5 0～ 80K     

La0.67-xErxSr0.33MnO3 (0.00≤x≤0.20)体系的磁电特性和低温电阻率反常

实验研究了La0.67-xErxSr0.33MnO3(x=0．00，0．10，0．20)体系的M-T曲线、ρ-T曲线和MR-T曲线。结果发现：随掺杂量增加，体系的磁结构从长程铁磁有序向自旋团簇玻璃态过渡，极低温区出现M-T曲线上翘；体系的电阻率随掺杂量的增加而增加，并出现低温极小值现象。体系磁电性质的变化来源于掺杂引起的额外磁性耦合，以及晶格畸变和局域磁矩引起的类似于磁性杂质对电子自旋散射造成的近藤效应(Kondo Effect)。     

Pr2O3掺杂SnO2陶瓷电极的制备及性能表征

通过共沉淀法制备了掺杂Pr2O3的二氧化锡电极样品,主要研究了在SnO2陶瓷电极中添加不同含量的Pr2O3对形貌结构及性能的影响.借助于XRD和SEM分析试样的晶型结构和微观形貌,结果表明Pr2O3能促进二氧化锡晶粒长大,并产生新的第二相Pr2Sn2O7.当Pr2O3含量从1%增加到5%(质量分数)时,第二相依次增多并镶嵌在主晶格中.通过电阻率和力学性能的测定,发现掺杂3%Pr2O3有利于提高SnO2电极的烧结致密化和降低电阻率,过量的Pr2O3则会产生过多第二相而不利于致密化烧结.     

Ca,Sr掺杂的La2NiO4的电学性质

制备了一种新的固溶体La_(2-x)Ca_xNiO_4(0≤x≤1.4)并与固溶体La_(2-x)Sr_xNiO_4作了对比。它们都具有四方的K_2NiF_4结构,其晶胞参数和晶胞体积都随x的增加而减少。固溶体La_(2-x)Ca_xNiO_4的室温电阻率随x的增加而增加,而固溶体La_(2-x)Sr_xNiO_4的室温电阻率却随x增加而减小,这种电学性质上的差别可能是由于Sr或Ca掺杂后引起Ni的价态变化导致Ni~(3+)的电子构型转变而造成的。     

铜含量对La2/3Sr1/3MnO3的电输运及磁电阻的影响

先用溶胶-凝胶法制备出La2/3Sr1/3MnO3的颗粒系统, 然后用化学的方法将Cu材料引入到La2/3Sr1/3MnO3的颗粒表面, 形成(1-x)La2/3Sr1/3MnO3/xCu (x≤0.05)的复合样品. 实验表明 Cu含量较低(x＜0.02)时, 复合样品电阻率较大, 仅在低温区表现出大的磁电阻效应, Cu含量较高(x＞0.025)时, 复合样品的电阻率较小(～10-2 Ω·cm), 在室温附近(270～300 K)、 3 T的磁场下, 表现出较大的不随温度变化的磁电阻效应～10%.     

Die Kristallstruktur des W3CoB3 und der dazu isotypen Phasen Mo3CoB3, Mo3NiB3 und W3NiB3

Zusammenfassung Mo₃CoB₃, Mo₃NiB₃, W₃CoB₃ und W₃NiB₃ kristallisieren in einem eigenen Typ (W₃CoB₃-Struktur). Das trigonal prismatische Bauelement [T ₆B]^* ist zu Ketten vereinigt, wobei B₃-Gruppen entstehen. Die Phasen sind vermutlich Bor-reicher als obiger Formel entspricht.

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The crystal structure of W₃CoB₃ and the isotypic phases Mo₃CoB₃, Mo₃NiB₃, and W₃NiB₃

Mo₃CoB₃, Mo₃NiB₃, W₃CoB₃, and W₃NiB₃ were found to possess a new type of crystal structure (W₃CoB₃-structure type). Trigonal prismatic groups [T ₆B]^* are linked together forming chains in such a way that B₃-groups occur. These borides do probably exist with a larger amount of boron as to compared with the formula.

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Mit 2 Abbildungen     

γ-Nitro-γ-butyrolacton

γ-Nitro-γ-butyrolactone By oxidation of 3-(1-nitro-2-oxocyclohexyl)propanal ( 1 ) with KMnO₄, besides 3-(1′-nitro-2′-oxocyclohexyl)pripionic acid ( 2 ), the complete hydrolysis product 4-oxononanedioic acid ( 4 ) and the oxidized semi-hydrolysis product 5-(2-nitro-5-oxotetrahydro-2-furyl)pentanoic acid ( 3 ) were formed. The crystalline 3 decomposes at r.t. forming 4 and nitrous gases; its structure was established by X-ray determination.     

Synthesis of γγγ-trifluorocarbonyl compounds

γγγ-Trifluorocarbonyl compounds are easily obtained in a good yield by introduction of the 1,1,1-trifluoroethyl moiety (CF₃-CH₂-) on the -methylene group of a ketone.     

K3SbSe3, Rb3SbSe3 und Cs3SbSe3 – Synthese und Kristallstruktur

K₃SbSe₃, Rb₃SbSe₃, and Cs₃SbSe₃ – Synthesis and Crystal Structure The compounds K₃SbSe₃, Rb₃SbSe₃ and Cs₃SbSe₃ were synthesized by heating mixtures of Sb₂O₃ and an alkalicarbonate in a stream of hydrogen saturated by selenium in a temperature range between 750 °C and 800 °C. The compounds crystallize isostructural with Na₃AsS₃. A comparison of atomic distances and bond angles with those of the isostructural arsenic and bismuth compounds shows the effect of lone pairs.     

Freezing the polarization of CH3NH3PbI3 and CH3NH3PbI3-xClx perovskite films

Thin films of methylammonium lead halides, CH₃NH₃PbI₃ and CH₃NH₃PbI_3-xCl_x, were deposited onto symmetrical microstructured electrode arrays of gold or platinum on Si/SiO₂ wafers. Polarization studies were carried out on perovskite films under vacuum in the dark. For poling, a constant voltage was applied to the samples while the temperature was cycled between 295 K and 4 K. The measured current densities depending on the temperature showed distinct characteristics relating strongly to the crystal phase and the dielectric properties of the perovskite films. Voltage sweeps were carried out at different scan rates at specific temperature intervals after poling. The polarization of the films due to the migration of iodide vacancies in direction of the blocking perovskite/metal interface was frozen almost up to room temperature. Charge carriers were only able to cross the blocking barrier and contribute to the current where the ions have accumulated during poling. All J-V curves showed hysteresis: inverted and regular hysteresis at room temperature and below, respectively. Inverted hysteresis originates from the slow accumulation of ions at the blocking barrier, while regular hysteresis arises from a distortion in the adjacent crystals which will be discussed.     

Synthesis of some derivatives of 3-amino-3-desoxyerythrose and 3-amino-3-desoxy-D-3-erythrose

The synthesis of derivatives of 3-amino-3-deoxy-L-erythrose by LAH or LAD reduction of the oxime of 1,2-O-isopropylidene α-L -glycero-tetros-3-ulofuranose is described.     

3x-pyrrolizin-3-ones

Condensation of pyrrole-2-dithiocarboxylates with CH acids containing ester groups, in the KOH-DMSO system, was used to prepare previously unknown 1-alkylthio-3H pyrrolizin-3-ones. The latter, treated with secondary amines, are readily converted to the corresponding 1-amino derivatives.     

3-H-pyrrolizin-3-ones

Previously unknown 1-alkylthio-3H-pyrrolizin-3-ones have been obtained by the condensation of pyrrole-2-dithiocarboxylates with CH acids containing ester groupings in the KOH-DMSO system. On treating the products with secondary amines they are readily converted into the corresponding 1-amino derivatives.Irkutsk Branch of the Russian Academy of Sciences, Irkutsk 664033. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 919–924, July, 1996. Original article submitted May 2, 1996.