Exploring the electrical transport properties of La0.67Ca0.33MnO3 at different sintering temperatures

The La_0.67Ca_0.33MnO₃ polycrystalline ceramics were prepared by the co-precipitation method with ammonium carbonate as the precipitant and the influence of the sintering temperature on the electrical transport properties of the ceramics were investigated. XRD results show that the ceramic structures obtained are all perovskite structures, which belong to the Pnma space group. Scanning electron microscopy (SEM) photographs demonstrated that the average size of the grains with the sinter temperature increased from 5.78 μm at 1300 °C to 24.04 μm at 1475 °C. Meanwhile, when the sintering temperature reached 1450 °C, the TCR reached the maximal value (32.3%·K^?1), which was much larger r than the TCR at 1350 °C. The theoretical model analysis of the data leads to the conclusion that the conductive mechanism of the low-temperature metallic region and the high-temperature insulating region is dominated by the grain boundary scattering effect and the small-polariton hopping (SPH), respectively.

     

Impact of granularity on transport properties of mechanically stressed La0.67Ca0.33MnO3 films

(La,Ca)MnO₃ is one of so called collosal magnetoresistive materials and it is of interest to correlate its transport properties to film growth in order to optimize its performance. Two-hundred nanometers thick (100)La_0.67Ca_0.33MnO₃ films were grown by laser ablation on (100)SrTiO₃, (100)LaAlO₃ and (100)(LaAlO₃)_0.3+(Sr₂AlTaO₆)_0.7 substrates. The films were granular in structure with low angle boundaries between the grains. The volume of the unit cell was considerably smaller for films grown on a SrTiO₃ substrate than on LaAlO₃. At temperatures higher than the one where the spins order, the strongest response of resistivity on temperature ρ(T) was measured for those (100)La_0.67Ca_0.33MnO₃ films that had the smallest volume of the unit cell. An increase of the lattice parameter for a film was accompanied by a decrease of the resistivity. The films grown on (LaAlO₃)_0.3+(Sr₂AlTaO₆)_0.7 substrates had the best crystallinity and the largest magnetoresistance.     

Ti掺杂对La0.67Ba0.33MnO3磁性和磁电阻影响

系统地研究了Ti掺杂对La0.67Ba0．33MnO3颗粒材料磁性、电性和磁电阻效应的影响，随着Ti含量的增加，材料的磁化强度和居里温度快速下降，电阻率急剧增大，电阻率的峰值逐渐向低温移动。Ti的掺杂对材料低温下低场磁电阻影响不大，主要是显著提高了材料的本征磁电阻。1％的Ti掺杂使材料的室温磁电阻得到显著增强，1T磁场下，室温磁电阻达到-8．4％，比未掺杂的La0.67Ba0．33MnO3材料增强了50％。     

Mn代替代对La0.67Ca0.33MnO3电磁特性和磁电阻的影响

主要就Mn位用不同元素替代对La0 6 7Ca0 3 3 MnO3 磁性、输运行为和磁电阻的影响的实验结果作比较研究 ,证明Mn位元素替代可能是提高和调制锰氧化物CMR效应的一种有效方法     

La0.67Sr0.33MnO3中Bi的掺杂效应

将Bi2O3掺杂到用溶胶—凝胶法制备的La0.6Sr0．33MnO3(LSMO)微粉中,XRD测量结果证实有过量的Bi析出。随着Bi掺杂量的增加,LSMO／(Bi2O3)x/2材料电阻率发生明显变化,在x=(0—0．10)摩尔比的掺杂范围内,电阻率先上升后突然下降。当X=0．1时,电阻率比未掺杂样品下降了一个数量级。Bi掺杂对低温和室温磁电阻有着完全不同的影响。低温下,随掺杂量增加,磁电阻下降;室温下Bi的微量掺杂可以使磁电阻增大,掺入x=0.03Bi使室温磁电阻由-4.4％提高到-5．6％。     

Bi掺杂对La0.67Ca0.33MnO3化合物磁性和导电特性的影响

与La的离子半径基本相同的Bi掺杂对钙钛矿锰氧化物La0.67Ca0.33MnO3的磁性和电输运性质有显著影响。掺杂使居里温度和磁化强度单调降低，电阻率和磁电阻随掺杂量增加先得到加强，然后又随着掺杂量的继续增加而降低。掺杂量达x=0.2时，试样在5－300K温度范围内表现为半导体特性，在ρ（T）及M（T）曲线上有两个以上相变，认为是铁磁相互作用与电荷有序转变竞争的结果。     

Microstructure, electrical and magnetic properties of polycrystalline La0.85K0.15MnO3 manganites prepared by different synthesis routes

Influence of different synthesis techniques (solid state reaction, sol–gel and co-precipitation) on the structure, microstructure, magnetic and electrical properties of polycrystalline La_0.85K_0.15MnO₃ (LKMO) sintered at 900 °C is investigated. All the as-synthesized compounds were confirmed as single phase and hexagonal structure at room temperature. The nano-crystallite size and average grain size were increased from the sample synthesized through solid state, sol–gel and co-precipitation techniques. The electrical and magneto-transport properties of polycrystalline LKMO was relied on the synthesis method. Significant decreases in metal–insulator transition temperature (T_p) with the increment of resistivity were observed for co-precipitation synthesized sample when comparing with solid state and sol–gel synthesized samples. Magnetization was decreased while ferro-paramagnetic transition temperature (T _c) was shifted toward lower temperature from solid state synthesized sample to co-precipitation synthesized sample. Furthermore, co-precipitation synthesized sample achieved the highest negative magnetoresistance at room temperature.     

Nb5+的掺杂对La0.67Sr0.33MnO3磁性和传输性的影响

将用溶胶-凝胶法制备的La0.67Sr0.33MnO3(LSMO)微粉与(Nb2O5)x/2粉在1100℃下混合烧结,形成了具有钙钛矿结构的锰氧化物与LaNbO4的复合体系,x是掺入的Nb5 离子与母体材料的摩尔比.在x=0.07的样品中得到最大电阻率为23.74 Ω·cm,比LSMO 高三个数量级.Nb5 离子的掺杂使样品的低场磁电阻(LFMR)和高场磁电阻(HFMR)效应都有所增强.77 K下,0.1 T和1 T磁场下在x=0.07 样品中分别得到24 % 和33.8 %的磁电阻效应,是LSMO样品的2倍和1.7倍.室温下x=0.05样品的磁电阻最大,为9 %.其中,LFMR来源于颗粒晶界处电子的自旋相关隧穿及散射作用,而HFMR来源于表面层的自旋非共线结构.     

衬底温度和生长氧压对La0.67Sr0.33MnO3:Ag0.08薄膜激光感生电压效应的影响

通过化学共沉淀法制备了La_0.67Sr_0.33MnO₃:Ag_0.08 (LSMO:Ag_0.08)多晶材料, 然后采用脉冲激光沉积(PLD)技术在LaAlO₃ (LAO)倾斜衬底上制备了LSMO:Ag_0.08薄膜。研究了衬底温度和生长氧压对薄膜结构、电输运特性及激光感生电压(LIV)效应的影响。结果表明: 当衬底温度为790℃、生长氧压为45 Pa时, 薄膜具有最大峰值电压(U_p)、优值(F_m)和各向异性Seebeck系数(ΔS); 在优化的衬底温度和生长氧压条件下, 长程Jahn-Teller协变引起ΔS数值提高, 这是LIV信号增强的主要原因。     

非正分钙钛矿锰氧化物(La0.8 Sr0.2)1-xMnO3的电磁特性

报道了A位缺位的钙钛矿锰氧化物(La0.8Sr0.2)1-xMnO3(0≤x≤0.30)多晶样品的相结构、磁性和磁电阻效应.实验表明,当x≥0.20时,化合物主要由磁性钙钛矿相和非磁性Mn3O4相所组成.它们的电阻率随温度的变化曲线均具有双峰特征,高温侧的电阻率峰出现在钙钛矿相的居里温度附近,低温侧的电阻率宽峰则是金属导电性的钙钛矿晶粒和高电阻率的半导体或绝缘体导电性的晶界或相界共同作用的结果.样品的零场电阻率ρ0随着A位缺位量x的增大而增大.适当改变x值,可以改善磁电阻比的温度稳定性.当x=0.30时,化合物磁电阻比MR在一个相对宽的温度范围内(175～328K)基本上保持不变,即MR=(9.1±0.5)%.     

Structural, magnetic and electrical properties of Fe/Cu/Fe films

A set of sandwich films in the configurations, Fe(200 nm)/Cu(t)/Fe(200 nm); t = 20 nm, 40 nm, 60 nm, 80 nm, 100 nm and 200 nm have been grown using thermal and electron beam gun evaporation techniques at a temperature of 473 K, under high vacuum conditions. The structure and crystallite sizes of the films were investigated by grazing incidence X-ray diffraction (GIXRD). The microstructure was examined by scanning electron microscope (SEM) studies. Average grain size and surface roughness were determined by atomic force microscope (AFM). The room temperature magnetization as a function of field has been measured using the vibrating sample magnetometer (VSM). The results revealed the existence of antiferromagnetic (AF) coupling between Fe layers through an interfacer Cu layer. The strength of AF coupling was observed to be increasing with increasing t and became maximum for t = 60 nm and, decreases for further increase in t. The behavior of coercive field with t indicated softness of the films. The low temperature electrical resistivity in the range from 4.2 K to 300 K has been measured. The residual resistance ratio, RRR and the temperature coefficient, TCR were determined. The power laws for the resistivity variation with temperature have been established. This is for the first time that a set of sandwich films in the present configurations were investigated for structural, magnetic and electrical properties and, the power laws for resistivity variation at low temperature have been established.     

BaPbO3/Ag复合体系大功率厚膜电阻浆料的研究

提出以BaPbO3/Ag复合体系作为功能相制备低成本大功率厚膜电阻浆料的思想,研究Ag含量、峰值烧结温度对厚膜电阻电性能和热稳定性的影响,并从导电机理方面对实验结果进行了分析讨论.     

Electrical and structural properties of Ta-N thin film and Ta/Ta-N multilayer for embedded resistor

Ta/Ta-N multilayer has been developed to control temperature coefficient of resistance (TCR) in a thin-film embedded resistor with the incorporation of Ta layer (+ TCR) inserted into Ta-N layers (− TCR). Electrical and structural properties of sputtered Ta, Ta-N and the multilayer films were investigated. The stable resistivity value of 0.0065 Ω·cm in β-Ta film was obtained, and phase change from fcc-TaN to orthorhombic Ta₃N₅ in Ta-N films was observed at nitrogen partial pressure of 22%. The multilayer of Si/Ta(60 nm)/Ta₃N₅(104 nm)/Ta(60 nm)/Ta₃N₅(104 nm) showed TCR value of − 284 ppm/K, where TCR of Ta was − 183 ppm/K and that of Ta₃N₅ was − 3193 ppm/K.     

Influences of Film Thickness on the Electrical Properties of TaN_x Thin Films Deposited by Reactive DC Magnetron Sputtering

TaNx thin films were deposited on commercial polished Al2O3 ceramic substrates by reactive dc magnetron sputtering. The influences of the film thickness on the electrical properties of the samples were examined in detail. It is found that the film thickness does not influence the phase structures of the TaNx thin films. The sheet resistances of the samples shift from 173 Ω/sq. to 7.5 Ω/sq. with the film thickness shifting from 30 nm to 280 nm. With the increase of the film thickness from 30 nm to 280 nm, th...     

Effect of B-doping on the structural, magnetotransport and magnetocaloric properties of La0.67Ca0.33MnO3 compounds

In this study, the effect of Mn site substitution of B on the structural, electrical and magnetocaloric properties of manganites was investigated. Polycrystalline manganites with the chemical composition La_0.67Ca_0.33Mn_1−xB_xO₃ (x = 0, 0.1, 0.2 and 0.3) were prepared by the standard solid-state process. It was found that the magnetisation, the Curie temperature and the maximum value of the magnetic entropy change |ΔS_m| decrease with increasing concentration of B.     

La3+掺杂对(Sr,Ba,Ca)TiO3基压敏陶瓷结构和性能的影响

采用常规固相法制备(Sr,Ba,Ca)TiO3基压敏陶瓷.用Nb5 离子取代Ti4 离子,Mn作受主掺杂元素的前提下,系统研究了稀土离子La3 施主掺杂对压敏陶瓷结构和性能的影响.结果表明,当La2O3=0.4%(摩尔分数)时,(Sr,Ba,Ca)TiO3基压敏陶瓷可获得良好的电性能:其压敏电压V10mA=11.19V,非线性系数α=2.93,电容C=31.16nF,介电损耗tanδ=0.43%,压敏电压温度系数KV10mA=0.1%/℃.     

The Effect of Co Substitution on the Crystal Structure and Electrical Resistivity of (La0.85Ag0.15)MnO3 Compounds

The effect of Co substitution on the crystal structure and electrical transport properties of La_0.85Ag_0.15Mn_1−y Co _y O₃ compounds (0≥y≤0.50) has been studied. Structural transition from rhombohedral to orthorhombic symmetry has been observed with Co doping. The lattice parameters are found to increase with doping up to y=0.20, then it decreases. It is explained on the basis of transition from high spin state to low spin state of Co ions with increase in doping beyond y=0.20. Ferromagnetic (FM) metallic behavior with colossal magneto-resistivity has been observed up to y=0.10. However, for y≥0.15 compounds, the temperature dependence of resistivity ρ(T) follows semiconducting behavior. The electrical resistivity in the metallic region could be explained based on electron–electron and electron–magnon scattering mechanisms. The data in the semiconducting region could be explained based on the variable range hopping model for y=0.2 and adiabatic small polaron hopping model for y≥0.3.      

La3+掺杂对堇青石陶瓷的相组成和性能的影响

为了获得堇青石含量高且具有一定孔隙率的堇青石质耐火材料,用X射线衍射仪,差热分析仪等手段研究了由溶胶-凝胶法（Mg盐、Al盐和正硅酸乙酯按堇青石化学计量比配制）制备堇青石陶瓷时,添加La^3＋对堇青石陶瓷相组成和性能的影响,分析了La^3＋在烧结过程中的作用机理。试验表明,随着烧结温度的提高,La^3＋含量的增加,该陶瓷的致密度、弯曲强度逐渐提高,而气孔率逐渐下降。适量添加La^3＋（质量分数为4％～6％）,显著降低中间相（尖晶石、方石英等）的含量。La^3＋的作用主要是作为烧结助剂,降低烧结温度,提高致密度。     

PbO-B2O3基玻璃对(Pb,Ca,La)(Fe,Nb)O3陶瓷微波介电性能的影响

基于玻璃形成理论和能量最小原理了玻璃组元与PCLFN陶瓷的微波介电性能之间的关系。PbO-B2O3基玻璃添加剂能够降低PCLFN陶瓷的烧结温度100－150℃。当PCLFN在1000－1050℃空气中烧结，Qf=3945-4796GHz，介电常数K＝100。PbO-B2O3基玻璃的组成也会影响PCLFN陶瓷的微波介电性能。三种PbO－B2O3基玻璃中，PbO-B2O3-V2O5玻璃是最有效的烧结助剂。