（1-x）La2／3Ca1／3MnO3／xCr2O3复合材料的电输运性质和磁电阻效应

用固相反应法制备了（1-x）La2／3Ca1／3MnO3/xcr2O3（x为摩尔分数）复合样品，实验研究了在外加0～3T的磁场下，Cr203含量对该复合样品的电输运性质及磁电阻的影响。结果发现随着Cr2O3含量的增加，金属．绝缘体（M-I）转变温度耳急剧降低，并且当Cr2O3，含量x〉0．1时此转变消失。与此同时，电阻率随其含量增加而快速增大，特别的是在样品中观察到了较宽温度范围内显著增强了的磁电阻。这种结果的出现可能与Cr2O3有关的新相偏析在La2／3Ca1／3MnO3（LCMO）晶界和颗粒界面有关。     

La1-xKxMnO3的微波吸收特性

用溶胶-凝胶法制备La1-xKxMnO3粉晶,用X射线衍射仪和扫描电镜表征样品的晶体结构和微观形貌,用微波矢量网络分析仪测试了该样品在2~18 GHz微波频率范围的复介电常数和复磁导率,并计算损耗角正切及微波反射率,分析K掺杂量和样品厚度对体系微波吸收性能的影响及微波损耗机制。结果表明:晶体结构为钙钛矿型,颗粒形貌为不规则椭球状或短棒状;当样品厚度为2.40 mm、x=0.3时,吸收峰值为27.1 dB,10 dB以上有效吸收频带宽度达10.6 GHz。纳米La1-xKxMnO3兼具介电损耗和磁损耗,介电损耗相对较强。磁损耗因子和介电损耗因子随微波频率的变化相反,是基体中铁磁与反铁磁团簇在微波电磁场作用下相互转变引起。     

高分子辅助沉积法制备Sm x Nd1- x NiO3 外延薄膜

采用高分子辅助沉积法制备掺杂不同钐（Sm）含量的Sm_xNd_1-xNiO₃外延薄膜（钐掺杂量x=0.5,0.55,0.6）。X射线衍射（特征θ-2θ扫描、摇摆曲线和φ-scan）和扫描电子显微镜的测试结果表明,制备的薄膜结晶性和外延性良好,与衬底的（001）取向保持一致。电阻率-温度曲线表明制备的外延薄膜均表现出金属绝缘体转变现象。随着Sm掺杂量的提高,金属绝缘体转变温度逐渐升高;当x=0.55时,外延薄膜的转变温度在室温附近。并且高分子辅助沉积法可以简单有效地制备热致变色外延薄膜。     

烧结温度对La0.6Ca0.4MnO3结构、磁性和磁致热效应的影响（英文）

研究了烧结温度对La0.6Ca0.4MnO3的结构、磁转变和磁熵的影响。观察表明,该化合物属于具有Pnma空间群的斜方晶系结构,不含任何杂质。研究烧结温度对居里温度(TC)的影响,发现提高烧结温度,TC稍有增大。磁致热效应研究显示,随着烧结温度的变化,磁熵会发生显著的变化。在外加磁场为3 T、烧结温度为1300°C时,相对冷却能(RCP)为89 J/kg。因此,该化合物可以考虑作为在室温附近或低于室温的潜在磁制冷材料。     

溶胶-凝胶法制备La0.67Sr0.33MnO3:Agx多晶材料及其性能

采用溶胶-凝胶法制备La0.67Sr0.33Mn O3∶Agx(LSMO∶Agx,x为摩尔百分比,x=0,0.04,0.08,0.10,0.20)多晶材料。通过XRD和R-T对LSMO∶Agx多晶材料的结构和性能进行分析。结果表明:在950、1050℃烧结的样品具有良好的单相结构。1050℃烧结时,Ag进入晶格替换A位La3+或Sr2+,使晶胞发生畸变、晶胞体积增大。Ag掺杂明显降低了样品电阻率,950℃烧结的Ag掺杂样品的电阻率降低了近两个数量级。提高烧结温度有助于改善LSMO材料的Tp和TCR。烧结温度由950℃变化到1050℃时,x=0样品的Tp增加了将近10 K,x=0.04样品的TCR从0.09%K-1上升到0.50%K-1。Ag掺杂能有效改善LSMO材料的电学性能。     

不同Ce掺杂比的La_(1-x)Ce_xMnO_3薄膜输运性质及机理研究（英文）

研究了电子型掺杂钙钛矿薄膜La_(1-x)Ce_xMnO_3的输运性质和外场作用下的输运机理。研究表明,La_(1-x)Ce_xMnO_3薄膜呈现出典型的金属-绝缘体转变,且与Ce的掺杂浓度相关。电阻-温度曲线表明,在低温时,电子-电子散射和磁畴对电子的散射是电阻形成的主要原因,而在高温下,小极化子的跳跃机制起主要作用。通过激光照射样品表面,发现光场诱导金属-绝缘体转变温度向着低温区偏移,该现象产生的原因在于La_(1-x)Ce_xMnO_3薄膜内部铁磁相与顺磁相的共存,此外,高能量的激光对样品的电阻变化影响更明显。进一步研究表明,Ce的掺杂浓度将会通过金属-绝缘相变对La_(1-x)Ce_xMnO_3薄膜的磁电阻效应产生显著的调制作用。     

非对称界面耦合对LaCoO3/LaMnO3 双层膜性能调控研究

通过高分子辅助溶胶凝胶自旋涂沉积法在（100）取向的SrTiO₃衬底上制备出LaCoO₃/LaMnO₃双层膜。在LaMnO₃表面生长一层LaCoO₃膜后,由于二者结构对称性差异,最终会在膜层界面处形成非对称界面耦合。由于非对称耦合作用,双层膜的铁磁转变温度从单层LaMnO₃的262 K下降为200 K。此外,由于界面处Mn-O-Co的双交换作用,与单层LaMnO₃薄膜的矫顽场相比,双层膜的矫顽场增大了约500%。研究结果表明,不同结构和性质的薄膜重组为多层膜的基础研究和高性能功能材料的应用提供了一种新的结构设计途径。     

溶胶-凝胶法制备La1-xSrxMnO3及其电磁性能研究

采用溶胶凝胶法,制备了La_1-xSr_xMnO₃(LSMO)纳米微粉。探究了Sr^₂₊的掺杂量对LSMO晶体结构、磁学性质、电磁特性和微波吸收性能的影响。结果表明,随Sr^₂₊含量的升高,样品的晶格常数和Mn-O-Mn键角增大,平均晶粒尺寸逐渐下降,样品出现从反铁磁性向铁磁性的转变,复介电常数呈先增大后减小的趋势。在2~18GHz内,x=0的样品在厚度为2mm时有最佳吸波效果,反射率小于-10dB对应的有效吸波频段为12.5~18GHz;Sr^₂₊的掺杂可使吸波频段有效的向低频移动,在X波段内,x=0.2的样品在厚度为2.3mm时的有效带宽达2.6GHz,证明LSMO是一种性能优异的介电损耗型吸波材料。     

La2O3与Sb2O3掺杂钛酸锶钡陶瓷的介电性能及相变（英文）

采用固相法制备La2O3与Sb2O3掺杂的钛酸锶钡陶瓷,研究其介电性能及相变特性。通过X射线衍射法分析体系微观结构并利用扫描电镜观察其表面微观形貌。(La,Sb)共掺杂的钛酸锶钡陶瓷具有典型的钙钛矿结构,且随着Sb2O3掺杂量的增多其平均粒径显著减小。La3+离子以及Sb3+离子均占据钙钛矿晶格的A位。La2O3与Sb2O3添加量的改变显著影响钛酸锶钡基陶瓷的介电常数以及介电损耗。La2O3改性的钛酸锶钡陶瓷其四方?立方相变为二级相变,且居里温度随着La2O3掺杂量的增多向低温方向移动。(La,Sb)共掺杂的钛酸锶钡陶瓷则体现为弥散相变,随着Sb2O3含量的增大而偏离居里-外斯定律越显著。由于Sb3+离子对晶格原位离子的取代使得(La,Sb)共掺杂的钛酸锶钡陶瓷的介电常数最大值下的温度亦随着Sb2O3含量的增大而降低。     

USb2单晶的生长及磁性和输运性质研究

采用Sb自助熔剂法成功生长高质量的USb₂单晶,并研究了磁化率、电阻、磁阻和比热等性质。研究表明,中等关联强度的USb₂中的5f电子具有巡游和局域双重特征。USb₂中的5f电子在260 K附近开始发生相干,203 K由顺磁态转变为反铁磁态,进行费米面的重构。在113 K以下局域的5f电子与传导电子发生第一次杂化使费米面附近电子结构发生变化。在54 K以下通过第二次杂化使得费米面附近形成了杂化能隙。在更低温度下晶体场效应对物理性质也产生了一定的影响。     

Colossal and constant magnetoresistance over a large temperature range between 230 and 4.2 K in La0.8Li0.2MnO3 prepared by a partial melting technique

La_0.8Li_0.2MnO₃ was prepared by a partial melting technique. The Li-doped LaMnO₃ compound has a rhombohedral perovskite structure and shows a wide semiconductor-to-metal transition between 230 and 175 K in resistance versus temperature. Nearly constant magnetoresistance, Δρ/ρ₀, above 20–60% was achieved with application of magnetic fields from 1 to 8 Tesla (T) over a very large temperature range from the ferromagnetic transition at 230–4.2 K. As a comparison, a partial melted La_0.7Ca_0.3MnO₃ shows a very narrow ferromagnetic transition around 230 K which is the same as that of single crystals and epitaxy thin films.     

Effect of high temperature sintering on the structural and the magnetic properties of La1.4Ca1.6Mn2O7

We investigate the effect of sintering temperature on the structural and magnetic properties of La_1.4Ca_1.6Mn₂O₇ double perovskite manganite compound prepared by the sol-gel route. Three sintering temperatures (1273, 1473 and 1673 K) are utilized for the heat treatment. Regardless of the sintering temperature, the tetragonal crystal structure with the I4/mmm space group is stable. However, a reduction in a and an increase in c lattice parameters along with a significant increase in crystallite-size occur on increasing the sintering temperature. This is also accompanied by the growth of grains. Grain-growth and changing crystallite-sizes account for the changes in magnetization, Curie temperature and magnetic entropy-change values. As the sintering temperature increases from 1273 to 1673 K the Curie temperature increases from 225 to 268 K and the magnetic entropy-change increases from 0.58 to 3.1 J kg⁻¹ K⁻¹ respectively.     

Magnetic entropy change in polycrystalline La1−xKxMnO3 perovskites

Polycrystalline samples of potassium doped lanthanum manganites having nanometric crystallite size have been synthesized by pyrophoric method. The Curie temperature (T_C) of the prepared samples is found to be strongly dependent on K content and spans between 260 and 309 K. Close to T_C, large change in magnetic entropy has been observed in all the samples. The maximum magnetic entropy change observed for samples with different concentration of K, exhibits a linear dependence with the applied magnetic field. Adiabatic temperature change at T_C at 1 T also increases with K doping and attains a maximum of 2.1 K for La_0.85K_0.15MnO₃. Estimated relative cooling power of La_1−xK_xMnO₃ compounds is nearly one-third of pure Gd. In addition to the tuneability of T_C between 260 and 310 K, higher chemical stability, lower eddy current heating and inexpensive preparation technique; the magnetic entropy change in La_0.85K_0.15MnO₃ compound at 1 T magnetic field is found to be 3.00 J/kg K and is 89% to that known for the prototype magnetic refrigerant (pure Gd). Our result on magnetocaloric properties suggests that La_1−xK_xMnO₃ compounds are attractive as a possible refrigerant for near room temperature magnetic refrigeration.     

Structural, magnetic and magnetotransport properties of La0.8Sr0.2MnO3/xLaMnO3 composites

The effect of LMO doping on the structure, magnetic and magnetotransport properties of La_0.8Sr_0.2MnO₃ (LSMO)/xLaMnO₃ (LMO) has been investigated. Two types of LSMO/xLMO composites, named as SL_x (low temperature sintered samples) and SH_x (high temperature sintered samples) samples, were prepared by different sintering temperature and solid-state reaction method. The presence of LMO at the grain boundaries increases the disordered states at the surface of the grains and therefore the magnetization and transition temperature decrease by increasing the amount of LMO doping level. Results show that the rate of decreasing of transition temperature is much more for high temperaure sintered samples. Also the resistivity of samples increases by the increase of LMO doping level. Results also show that the LMO doping has an effect on a low field magnetoresistance (LFMR). The value of LFMR increases for low doping level of 0 ≤ x ≤ 15, for SL_x samples and 0 ≤ x ≤ 10 for SH_x samples. Also LFMR decreases at high doping level. The spin dependent tunneling and scattering at the interfaces of the grain boundaries are responsible for the increase of LFMR at low doping level, while reduction of LFMR at high doping level may result from the grain boundary becoming too thick for electron tunneling.     

XPS study of Pr1−xCaxMnO3 (x = 0.2, 0.33, 0.4 and 0.84)

We have studied the Mn 2p, Ca 2p, and Pr 4d core levels of Pr_1-xCa_xMnO₃ (x = 0.2, 0.33, 0.4 and 0.84) as a function of x using X-ray photoelectron spectroscopy both at room temperature as well as 77 K. Suppression of chemical potential shifts have been observed at 77 K compared to that of room temperature spectra. We have discussed this result by considering the concept of phase separation.     

Emissivity of La1-xSrxMnO3/acrylic Resin Thermal Control Coating

Thermal control coatings were fabricated by mixing of La1-xSrxMnO3(LSMO)powder and acrylic resin and brushed on Al alloy substrate.The powders of La0.7Sr0.3MnO3 and La0.8Sr0.2MnO3 were prepared using sol-gel method.XRD results reveal the phase structure of LSMO powders are perovskite.The transition temperature from metal to insulator of La0.7Sr0.3MnO3 and La0.8Sr0.2MnO3 are 300 and 275 K,respectively.The emissivity evolution with temperature of the coatings was measured.For La0.7Sr0.3MnO3/acrylic resin coating,the emissivity increases from 0.56 to 0.88,and for La0.7Sr0.3MnO3/acrylic resin coating from 0.50 to 0.90.     

Influence of grain size on magnetic and transport properties of polycrystalline La0.8Sr0.2MnO3 manganites

In this study, we have investigated the effects of grain size on the magnetic and transport properties of polycrystalline La_0.8Sr_0.2MnO₃ samples. The samples were prepared by solid-state reaction method. In order to obtain a series of samples with different grain sizes, the bulk sample was subjected to high energy ball milling. The magnetization decreases by decreasing grain size. A decrease in magnetization by decreasing grain size is due to the increasing of magnetically disordered states at the surface of grains. By decreasing the grain size the resistivity increases and a second peak was observed at temperatures well bellow T_c. The intrinsic CMR decreases by decreasing grain size while the extrinsic intergranular MR is promoted to larger values. A model, proposed by Zhang et al. [N. Zhang, W. Ding, W. Zhong, D. Xing, Y. Du, Phys. Rev. B 56 (1997) p. 8138.], involving domain walls contribution and a spin polarized tunneling between neighboring grains of manganites below transition temperature may be responsible for this behavior.     

La2/3Ca1/3MnO3∶Ag0.4与La2/3Ba1/3MnO3∶Ag0.4的制备及其性能研究

采用化学共沉淀法合成制备了Ag掺杂摩尔百分比为0.4的La2/3Ca1/3MnO3∶Ag0.4 (LCMO∶Ag0.4)、La2/3Ba1/3MnO3∶Ag0.4(LBMO∶Ag0.4)多晶复合材料,通过XRD和R-T分别对两种材料的结构和性能进行测试分析.实验结果表明:所得样品均为正交晶系钙钛矿结构;LCMO∶Ag0.4的金属-绝缘转变温度(Tp=280.2 K)比LBMO∶Ag0.4要高(Tp=256.8 K);LCMO:Ag0.4样品的电阻值比LBMO∶Ag0.4要小两个数量级;LCMO∶Ag0.4的TCR最大值为28％,要远远高于LBMO∶Ag0.4的TCR最大值(0.5％).