Magnetic and electric properties of Bi(La)Sr(Ca)Mn2O6

Bi1-xLaxSrMn2O6 and BiSr1-xCaxMn2O6 are prepared by solid state reaction. They are n-type semiconductors with ferromagnetism at room temperture. When Bi is substituted partly by rare earth, a negative magnetoresistance effect is observed in the pellet of Bi1-xLaxSrMn2O6. There are semiconductor-metal transitions at 820 K in BiSrMn2O6. The transitions are attributed to the magnetic transition at high temperature. The substitution of Ca for Sr makes the transition temperature increase. However, when Bi is partly substituted by La, the solid solution does not change into metal. (C) 1996 Academic Press, Inc.

MMgF_4(M=Ca,Sr,Ba)体系中Eu和Tb的电荷迁移

于不同气流中,合成了MMgF_4:xEU,yTb复合氟化物燐光体.该体系中Eu~(3+)和Eu~(2+)共存.Tb的存在影响Eu的价态存在形式.ESR���试表明,随Tb的掺入浓度增加,Eu~(2+)的浓度呈规律性变化.随Eu的掺入,样品的XPS谱中出现了四价铽的Tb_3d(5/2)特征伴峰.认为Eu~(3+)和Tb~(3+)之间存在电荷迁移平衡.即Eu~(3+)+Tb~(3+)(?)Eu~(2+)+Tb~(4+).通过半定量手段研究了SrMgF_4中这一平衡的平衡常数.

Ce~（3＋）在钙钛矿型KMF_3（M＝Mg、Ca、Sr���Ba）基质中的发光特性

采用高温固相反应法，在Ａｒ气氛中合成了ＫＭＦ３（Ｍ＝Ｍｇ、Ｃａ、Ｓｒ、Ｂａ）基质化合物和掺杂Ｃｅ３＋的磷光体。经Ｘ射线衍射分析确定，ＫＭｇＦ３和ＫＣａＦ３属于立方晶系、钙钛矿型结构，ＫＳｒＦ３和ＫＢａＦ３具有类似的结构。测定了ＫＭＦ３∶Ｃｅ３＋的发光光谱，观察到与其结构对应的分为二种不同的光谱结构，讨论了Ｃｅ３＋的取代格位

Studies on the synthetic, structural, electrical and magnetic properties of Ln(n)MCo(n)O(3n+1) (Ln=Sm, Gd; M=Sr, Ba; n=1,2)

Three new oxides Sm2SrCo2O7, Sm2BaCo2O7 and Gd2SrCo2O7 have been synthesized successfully by solid state reaction mathod. The X-Ray diffraction spectra show that they are all isostructural with Sr3Ti2O7, and Ln(2)SrCo(2)O(7)(Ln=Sm,Gd) crystallized in tetragonal system, Sm2BaCo2O7 in orthrhombic system. The Co-O bonds in CoO2 planes of Ln(2)SrCo(2)O(7) are shorter than those of LnSrCoO(4)(Ln=Sm, Gd), and so their delectrons are more delocalized and their electrical resistivities are smaller. The electrical resistivities versus temperature in the range 300 similar to 1100K showed that the five brides show the characters of weakly localized systems. In the lower temperature range, the magnetic behaviors of Gd2SrCo2O7 and GdSrCoO4 fit Curie-Weiss law well, and the magnetic exchange reaction in CoO2 sublattices of Gd2SrCo2O7 is ferromagnetic, but that of GdSrCoO4 is antiferromagnetic. The other three oxides with Sm3+ showed complex magnetic behaviors which is perhaps related with the complexity of Sm3+.

THE EFFECT ON PHYSICAL-PROPERTIES OF THE SUBSTITUTION OF CA OR BA FOR SR IN NDSRNIO4

A new solid solution series, NdSr(1-x)M(x)NiO(4) (M = Ca: 0.0 less than or equal to x less than or equal to 1.0; M = Ba: 0.0 less than or equal to x less than or equal to 0.6), was synthesized by solid state reaction, and the structures, magnetic and electrical properties and optical spectra of this series have been studied. All the samples crystalized in tetragonal systems, with the exception of NdCaNiO4, which crystallized in the orthohombic system. IR spectra of NdSr1-xCaxNiO4 indicated that the lengths of two Ni-O bonds decrease with increasing Ca content. The electrical conduction changed from metallic-type to semiconductive-type when x greater than or equal to 0.4 (M = Ca, Ba), and the room temperature resistivities of NdSr1-xCaxNiO4 increased with the increase of Ca content. Magnetic susceptibility measurements revealed that Ni+3 ions in all the samplies were in low-spin state over the temperature range 77-300 K.

A STUDY OF SURFACE OXYGEN SPECIES FROM LA-ME-O (ME=MG, CA, SR, BA) CATALYSTS FOR METHANE OXIDATIVE COUPLING

CO2-TPD was used to study the surface basicity of La-Me-O mixed oxides and O-2-TPD, CH4-TPD were employed to study the surface active oxygen species. Comparing the CO2-TPD with O-2-TPD, we can see that the basicity of catalyst is in parallel with the catalystic activity. The stronger basicity is more profitable for the catalyst to adsorb oxygen to form active oxygen species and to activate CH4 by breaking a C-H bond, By comparing the catalytic activity, the results showed that La-Ba-O(La/Ba=7/3) catalyst had the strongest basicity, and it gave the highest CH4 conversion and C-2 selectivity, The results from the pulse reaction showed that the lattice oxygen participated in the OCM reaction without gas oxygen, and it was the selective oxygen species.

STUDIES ON THE SYNTHETIC, STRUCTURAL, ELECTRICAL, AND MAGNETIC-PROPERTIES OF THE NEW LAYERED OXIDES LN(2)MCO(2)O(7) (LN=SM, GD, M=SR, BA)

Three new oxides Ln(2)MCo(2)O(7) (Ln = Sm, Gd; M = Sr, Ba) have been synthesized in solid state reaction method. The powder X-ray diffraction spectra show that they are all isostructural with Sr3Ti2O7. The electrical resistivities in the temperature range 300-1100 K show that they are all semiconductors, and a transition to metals is observed at 1053, 1053, and 573 K for Sm2SrCo2O7, Gd2SrCo2O7, and Sm2BaCo2O7, respectively. The magnetic suspectivities of Gd2SrCo2O7 in the temperature range 300-673 K fit the Curie-Weiss law well. A plateau is observed in the curves of Sm(2)MCo(2)O(7) (M = Sr, Ba) which is attributed to the configuration state change of Co(III) from low spin to high spin. (C) 1995 Academic Press, Inc.

MMgF_4：Eu（M＝Ca，Sr���Ba）体系中铕离子的发光中心及价态

合成了铕离子激活的ＭＭｇＦ４．磷光体，研究了Ｅｕ３＋离子的光谱特征与基质化合物的关系，存在三类发光中心，讨论了基质组成对铕离子价态的影响。

甲烷氧化偶联La－Me－O（Me＝Mg，Ca，Sr���Ba）系催化剂表面氧种的研究

利用ＣＯ_２－ＴＰＤ法考察了Ｌａ－Ｍｅ－Ｏ（Ｍｅ＝Ｍｇ，Ｃａ，Ｓｒ，Ｂａ）系催化剂的表面碱性，并用Ｏ_２－ＴＰＤ、ＣＨ_４－ＴＰＤ法对该体系的表面活性氧种进行了表征，并与催化性能相关联。结果表明，Ｌａ－Ｂａ－Ｏ催化剂由于表面强碱性中心数目多，产生活性氧种的数目也多，有利于甲烷的活化，因而具有最高的甲烷转化率和Ｃ_２烃选择性。脉冲反应表明，在无气相氧存在下，表面晶格氧参与了氧化偶联，而且是选择氧化的活性氧种。

Ln_nMCo_nO_(3n+1)(Ln=Sm,Gd;M=Sr,Ba;n=1,2)的合成、结构、电和磁性质研究

用固相反应法合成了三个新的交生相氧化物:Sm_2SrCo_2O_7,Gd_2SrCO_2O_7和Sm_2BaCo_2O_7.它们均具有Sr_3Ti_2O_7型的结构,其中Sm_2BaCo_2O_7属于正交晶系,其它属于四方晶系.与LnSrCoO_4相比,Ln_2SrCo_2O_7(Ln=Sm,Gd)中CoO_2平面上的Co-O键缩短,电子离域化趋势增强,导电能力提高.在300～1100K之间,电阻率与温度关系表明,五个氧化物均表现弱定域系统的特性. 300～1100K之间的磁化率与温度关系表明,在较低温度下,GdSrCoO_4和Gd_2SrCo_2O_7符合Curie-Weiss定律,但前者的CoO_2平面上的磁交换作用是反铁磁性的,而后者是铁磁性的;含Sm~(3+)的三个氧化物表现出较为复杂的磁性质,这可能与Sm~(3+)离子磁性质的复杂性有关.

MF_2:Eu,Ce(M=Ca,Sr,Ba)中稀土离子的价态变化

我们已经实验证明并报道了Eu-Tb之间、Ce-Yb之间的电荷转移.本文首次实验证实了Ce~(3+)离子和Eu~(3+)离子之间电荷转移现象的存在,进一步阐述了稀土价态与其电子组态共轭特征的相关性.1 实验部分1.1 试剂CaF_2,SrF_2,BaF_2,NH_4HF_2、氢氟酸、盐酸均为分析纯,EuF_3和CeF_3分别由高纯Eu_2O_3(99.95%)及CeO_2(99.99%)自制.1.2 MF_2:Eu,Ce体系的合成按化学计量比(MF_2:X%CeF_2,y%EuF_3;X=1,y=0,0.1,0.3,0.5,1;X=0,0.05,0.1,0.3,0.5,y=1)准确称取原料,放人玛瑙研钵中充分研混后装入刚玉柑涡中,置于管状炉内(用氢气

THE SYNTHESIS AND PHYSICAL-PROPERTIES OF THE NEW LAYERED LANTHANIDE ALKALINE-EARTH COBALT OXIDES [LN2MCO2O7 (LN=SM,GD M=SR,BA)]

Three new oxides Sm2SrCo2O7, Sm2BaCo2O7 and Gd2SrCo2O7 have been successfully synthesized by a solid state reaction method.The X - Ray diffraction spectra show that they are all isostructural with Sr8Ti 2O7, Ln2SrCo2O7(Ln=Sm, Gd) crystallized in the tetra

A STUDY OF SITE OCCUPATION OF EU-3+ IN ME2Y8(SIO4)6O2 (ME=MG, CA, SR)

Alkaline earth (Mg, Ca. Sr) yttrium silicate oxyapatites doped with Eu3+ show red luminescence with comparable intensity. In this system of phosphors, the Eu3+ ions enter 4f sites and 6h sites simultaneously according to the fluorescence spectra, in which

掺Ce~（3＋）、Tb~（3＋）的M_3Y_2（BO_3）_4（M＝Ca，Sr���

采用固相反应的方法；经二次灼烧合成了掺Ｃｅ（３＋）、Ｔｂ（３＋）的Ｃａ３Ｙ２（ＢＯ３）４和Ｓｒ３Ｙ２（ＢＯ３）４磷光体；分析了合成过程中铈的还原情况．用Ｘ－射线衍射分析确定了它们的结构均为正交晶系，空间群Ｐ２１ｃｎ测定了Ｃｅ（３＋）和Ｔｂ（３＋）在两种基质中的光谱，得到Ｃｅ（３＋）波长位移的某些规律，观察到Ｃｅ（３＋）对Ｔｂ（３＋）的敏化作用．