Sr离子含量的减少对于La0.60Sr0.25Na0.15MnO3材料性能的影响

利用溶胶-凝胶法（sol-gel）制备了稀土锰氧化物多晶样品La0.60Sr0.25-xNa0.15MnO3,发现随着Sr离子含量的减少,样品在室温附近庞磁电阻效应有了明显的改善。在1.8 T的磁场下,对于x=0.05的样品,其CMR值在240~320 K的温区范围内均保持在5.3%（±0.2%）,温度稳定性有显著改善。     

退火温度对La0．7Sr0.3MnO3薄膜取向的影响

在LaAlO3(100)单晶上,通过化学溶液法(CSD)制备了有取向性的La0.7Sr0.3MnO3薄膜,对不同退火温度下薄膜的取向性进行了研究.结果表明:随着温度的升高,薄膜的取向性变好.     

La0.67Sr0.33Mn0.7Fe0.3O3的制备及其光催化性能研究

采用溶胶—凝胶燃烧法制备了纳米级钙钛矿型复合氧化物La_0.67Sr_0.33Mn_0.7Fe_0.3O₃,通过XRD、SEM对样品的物相和形貌进行表征,结果表明所得La_0.67Sr_0.33Mn_0.7Fe_0.3O₃样品为钙钛矿结构,直径约为50纳米,长度为1μm.以350 W氙灯做光源,催化降解亚甲基蓝水溶液,反应6 h,降解率达到96%.     

Preparation of La0.9K0.1CoO3 Perovskite Composite Oxide

Two methods for preparing La0.9K0.1CoO3 perovskite composite oxides.traditional solid state reaction method and sol-gel method.were compared.The characteristics of the powders,such as purity.particle diameter,BET surface area,pore diameter,were inrestigated by using TG-DTA,XRD,SEM and BET methods.The experimental results shou that La0.9K0.1CoO3 perorskite composite oxide can be obtained by using the two methods.The purity of La0.9K0.1CoO3 powders can be increased by raising the calcining temperature while the particle diameter increased and BET surface area decreased.At the same calcining temperature,the properties of the La0.9K0.1CoO3 powders synthesized by the sol-gel method are superior to those synthesized by the solid state reaction method.such as purer phase,smaller particle diameter,which can be used as a satisfactory catalyst in diesel waste gas cleaning.     

La1-xCexMnO3凝胶晶化过程与微波吸收性能

用溶胶一凝胶法制备了La1-xCexMnO3粉体,根据DSC-TGA、FT-IR、XRD分析了样品的晶化过程,用圆柱体法测试了样品的室温电阻率,用微波网络分析仪测试样品的微波吸收性能．结果表明,样品凝胶在煅烧时经过脱水、剧烈分解、逐渐晶化等过程,900％左右形成稳定的钙钛矿结构并伴有少量CeO2杂相;室温电阻率处于半导体范围,且随掺杂量z增加而减小;样品厚度为2．2mm、x=0．4时,13．2GHz频率位置处微波吸收峰值为27dB,10dB频宽为3．2GHz．分析认为,合适的电阻率、钙钛矿晶体极化驰豫及共振、铁磁团簇转向及共振是材料具有良好微波吸收性能的原因．     

钙钛矿La0.5Sr0.5Mn1-χCrχO3的制备与磁性研究

采用溶胶-凝胶法制备了La0.5Sr0.5Mn1-χCrχO3(χ＝0.0-0.5)的系列样品,通过XRD,SEM和振动样品磁强计对样品进行表征,结果表明:随掺杂量χ的增加,样品结构从正交向单斜转变,对称性由高向低转变.样品形貌均为球形,颗粒尺寸在0.2-1 μm之间.样品的居里温度随掺杂量χ的增加而降低.     

Electrical Transport and Magnetic Properties of La0.67Ca0.33Mn1-xCrxO3 and La0.67＋xCa0.33-x Mn1-xCrxO3 （0.04≤x≤0.08）

A comparative study for two different series,La0.67Ca0.33Mn1-xCrxO3 and La0.67+xCa0.33-xMn1-x CrxO3,is performed with x changing from 0.04 to 0.08 through measurements of zero-field resistivity (ρ) magnetoresistance(MR) and ac susceptibility (x) as functions of temperature(T). For the second group,a single insulator-metal transition was characterized by the resistivity maximum appears in ρ VS.T curve.For the first group,besides the resistivity peak appearing at higher temperatures,the sample shows evidence for the existence of another peak appearing at lower temperatures.Compared to the first group,the second group shows a significant enhancement in MR effect,while the measurement of x-T dependence does not display obvious differences for the two series.Different behaviors observed in the tWO series are discussed by considering possible exchange interaction between Mn3+ ion and Cr3+ ion.     

Electrical Transport and Magnetic Properties of La0.67Ca0.33Mn1-xCrxO3 and La0.67＋xCa0.33-x Mn1-xCrxO3 （0.04≤x≤0.08）

A comparative study for two different series, La0.67Ca0.33Mn1-xCrxO3 and La0.67＋xCa0.33-x Mn1-xCrxO3 is performed with x changing from 0.04 to 0.08 through measurements of zero-field resistivity （p）, magnetoresistance （MR） and ac susceptibility （Z） as functions of temperature （T）. For the second group, a single insulator-metal transition was characterized by the resistivity maximum appears in p vs. T curve. For the first group, besides the resistivity peak appearing at higher temperatures, the sample shows evidence for the existence of another peak appearing at lower temperatures. Compared to the first group, the second group shows a significant enhancement in MR effect, while the measurement ofΧ-T dependence does not display obvious differences for the two series. Different behaviors observed in the two series are discussed by considering possible exchange interaction between Mn^3- ion and Cr^3- ion.     

多晶La0.49Sr0.51MnO3中的铁磁反共振

采用谐振腔微扰技术测量了多晶La0.49Sr0.51MnO3的微波吸收（PMA）,观察到在居里温度TC 或奈尔温度TN附近发生PMA呈现极小值即铁磁反共振（FMAR）现象. 基于朗道-利弗希茨-吉尔伯特模型,磁化强度μ0M对温度的依赖关系可以从FMAR得到. 发现当外加直流磁场μ0H = 0时,不同微波频率下得到的磁化强度μ0M对温度的依赖关系与标度律符合. 然而,当μ0H ≠ 0且μ0H＜120 mT时,不同μ0H下得到的磁化强度μ0M对温度的依赖关系与标度律不符合. 在μ0H平行最大微波磁场hrf时,在TC 附近随μ0H增加发生FMAR的PMA值增加,且随μ0H增加发生FMAR的温度下降,但此时在TN 附近未观测到FMAR. 在μ0H垂直hrf时在TC 附近随μ0H增加发生FMAR的PMA值减少,且随μ0H增加发生FMAR的温度很少变化,但此时在TN 附近发生FMAR的PMA值和温度均几乎不随μ0H变化. 这些结果可归因为：①多晶La0.49Sr0.51MnO3是一种由铁磁（FM）和反铁磁（AFM）等多态微区组成的密切合物,是一个包含多个状态和取向互不相同的畴壁的复杂系统;②在μ0H增强或温度下降的过程中,都存在导致PMA增加或减少的两种机制的竞争.     

DC and AC transport properties on La0.8Sr0.2MnO3

Railway Engineering Science - Magnetoresistive sensor can be widely used in modern transportation field, such as the vehicle positioning and navigation system, vehicle detection system, and...     

La1-xZnxMnO3和LaL2/3 Sr(1-x)/3 Znx/3 MnO3的磁电输运特性

用固相反应方法制备La1-xZnxMnO3和La2/3Sr(1-x)/3Znx/3MnO3化合物.La1-xZn MnO3在不同掺杂浓度x的研究表明:Zn2 在一定浓度范围内掺杂,具有钙钛矿结构,但掺杂浓度在50%～70%时有ZnO衍射峰,其电阻率在100 K以上随温度而下降,当掺杂浓度为x=0.3时电阻率最低.当Zn2 和Sr2 共掺而保持La3 浓度不变,即载流子浓度不变,维持Mn3 /Mn4 =2∶1,随Zn2 掺杂浓度增大,铁磁-顺磁转变温度降低,磁阻效应增大.低场磁阻效应与Zn2 掺杂浓度无关,而与温度有关;高场磁阻效应随掺杂浓度增大而增大.     

蜂窝陶瓷型La0．8Sr0.2MnO3催化剂VOCs催化燃烧反应活性

以堇青石(CH)为第一载体,六铝酸盐(HA)为第二载体(washcoat),La0.8Sr0.2MnO3(LSM)为活性物种,制备了LSM/HA/CH催化剂.XRD表征发现,LSM具有完善的钙钛矿晶型.SEM观察表明,活性物种在涂层表面分散均匀.通过对苯、甲苯、二甲苯、乙酸乙酯、丙酮和乙醇六种有机物的性能测试,发现LSM/HA/CH对上述六种有机物均具有很好的催化活性,特别是对乙酸乙酯等含氧有机物表现出更好的燃烧性能,在10000 h-1空速下,反应温度为240℃时即可将含氧有机物完全燃烧.     

自蔓延高温合成La0.67Sr0.33MnO3-δ粉体的研究

采用自蔓延高温合成(SHS)技术合成了La0．67Sr0．33MnO3-δ粉体。研究了KMnO4含量、压坯密度对燃烧反应及退火温度对粉体性能的影响，并用XRD、SEM对粉体的性能进行了表征，结果表明：KMnO4用量为0．3时，反应完全且晶粒大小均匀；反应的原料混合物压坯密实度的降低可使燃烧温度有所增大；最佳退火温度为1100℃。     

钙钛矿型La0.8Sr0.2MnO3催化剂对氯苯催化燃烧的性能研究

采用共沉淀法制备了钙钛矿型La0.8Sr0.2MnO3催化剂,用XRD,SEM,BET对催化剂进行了表征,考察了催化剂对氯苯的催化燃烧性能.结果表明:La0.8Sr0.2MnO3催化剂呈现钙钛矿晶型,催化剂具有较好的分散性,颗粒尺寸约为60 nm,对氯苯有较好的催化燃烧性能.在氯苯浓度为800~1 600 mg/m3,空速(GHSV)为1 000~4 000 h-1的情况下,反应温度高于350℃时,氯苯几乎能完全去除.稳定性实验结果表明:该催化剂在氯苯浓度为800 mg/m3,空速(GHSV)为1 000 h-1,反应温度为410℃的条件下,经历了100 h连续催化燃烧后,没有出现明显失活,说明La0.8Sr0.2MnO3催化剂对含氯有机物具有较强的抗毒性.     

高温对钙钛矿La0.65Ca0.18Sr0.17MnO3形貌及磁热效应的影响

采用水热合成法制取了La0.65Ca0.18Sr0.17MnO3钙钛矿粉末.通过X射线衍射仪(XRD)测量与扫描电镜(SEM)观测,发现高温不改变纯的La0.65Ca0.18Sr0.17MnO3的晶体结构,但对立方相的La0.65Ca0.18Sr0.17MnO3的形貌有一定影响.在1.4 T的磁场下,利用自制的ΔTad-T曲线测量仪测得La0.65Ca0.18Sr0.17MnO3样品的磁热效应,结合其在0.01 T下的M-T曲线图,得出高温影响钙钛矿样品磁热效应测量的实质是:高温改变了钙钛矿粉末的致密度从而影响对其磁热效应测量的准确性.     

钙钛矿型La_(0.67)Sr_(0.33)Mn_(1-x)Fe_xO_3的室温磁热效应和磁致伸缩效应

采用溶胶-凝胶工艺制备了La0.67Sr0.33Mn1-xFexO3多晶样品,并研究了其晶体结构、磁热效应及室温下的磁致伸缩效应.其X射线衍射谱表明,所有样品均为钙钛矿结构单相,分析表明,随Fe含量的增加,材料的铁磁居里温度(TC)下降,磁致伸缩系数先增加后降低.