La_(0.65)Sr_(0.35-x)Na_xMnO_3的磁卡效应

采用溶胶-凝胶技术制备了钙钛矿型稀土锰氧化物La0.65Sr0.35-xNaxMnO3(x=0.05,0.10,0.15),利用X射线衍射(XRD)和振动样品磁强计(VSM)对样品的结构、居里温度和磁卡效应进行了研究。结果表明,随着Na含量的增加,晶胞体积减小,居里温度提高,当x=0.15时,La0.65Sr0.35-xNaxMnO3的最大磁熵变达到了1.66 J/(kg.K)。     

钙钛矿La_(0.7)Sr_(0.3)MnO_3的形态及居里温度的研究

采用溶胶-凝胶法前躯体+混合(KCl+NaCl)熔盐法制备出了颗粒状和棒状的钙钛矿La0.7Sr0.3MnO3(LSMO)样品。利用XRD,VSM对样品结构进行表征,结果表明颗粒状的样品尺寸在200 nm左右,而棒状样品的直径在50 nm左右,长度一般在500 nm以上;颗粒状样品属于正交晶系,棒状样品属于四方晶系;棒状样品的居里温度(235 K)要比颗粒状样品的居里温度(374 K)低很多。     

(Gd_(1-x)R_x)_5Si_4(R=Dy、Ho)磁制冷材料的晶体结构以及居里温度研究

为了探索室温附近温度范围内的磁制冷材料 ,作者研究了 (Gd1 xDyx) 5Si4(x =0 1、0 2、0 3、0 3 5 )和 (Gd1 xHox) 5Si4(x =0 0 5、0 15、0 2 5 )系列合金的晶体结构、居里温度。结果发现 :该系列合金仍保持Gd5Si4的Ge4Sm4正交型结构 ;随着x量的增加 ,样品的晶格常数逐渐减小 ,居里温度TC在 3 40K～ 2 60K连续可调 ,并呈线性减小趋势 ;改变R的含量可以得到单一的居里温度值 ,该值和计算值基本吻合     

La(Fe_(1-x)Mn_x)_(11.4)Si_(1.6)间隙氢化物的磁性和磁热效应

系统研究了间隙原子H和Mn原子替代Fe对La Fe11.4Si1.6化合物磁性和磁熵变的影响。研究表明适量的Mn替代和间隙H原子的加入不改变化合物的立方Na Zn13型晶体结构。La(Fe1-xMnx)11.4Si1.6居里温度TC从205K(x=0)下降到156K(x=0.04)。随Mn含量的进一步增加,Fe-Fe原子间的铁磁耦合与Fe-Mn、Mn-Mn原子间的反铁磁耦合作用相当,在x=0.06和0.08的化合物中引起阻挫产生自旋玻璃行为。吸氢后的所有化合物都呈现出良好的铁磁行为,由于晶胞体积膨胀居里温度升高到室温附近,并在室温附近观察到大磁热效应。     

多晶La0.49Sr0.51(Mn1-xNbx)O3的磁电阻研究

采用四探针法测量多晶La0.49Sr0.51(Mn1-xNbx)O3(x=0,0.05,0.15和0.25)在磁场下的电阻率温度曲线.实验结果显示:①在0.45T磁场下,对于x=0和x=0.25的样品,几乎观察不到磁电阻(Magnetoresistance,MR)效应,而对于x=0.05和x=0.15的样品,磁电阻效应较明显.这种差异可能与样品中铁磁相是否占主导作用有关;②比较x=0.05和x=0.15这两种样品的MR机制,前者可能与载流子在弱连接晶界上的自旋相关散射有关,且其主要是非本征的;而后者主要是本征的.     

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.     

水热合成La1-x-yCayAxMnO3的磁热性能

采用水热合成法制取了钙钛矿型La1-x-yCayAxMnO3(A为Sr或Ba)化合物粉末.在1.4 T的磁场下,利用自制的ΔTad-T曲线测量仪测得其磁热效应,发现A离子的掺杂量x会使居里温度TC增加.依据拟合的曲线规律,控制化合物的成分,制得室温附近不同掺杂的镧锰氧化合物样品,估算的居里温度与实测值接近.     

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.     

Sr离子含量的减少对于La0.60Sr0.25Na0.15Mn3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.     

Sr_(1-x)(YK)_(0.25x)Ba_(0.5x)Bi_4Ti_4O_(15)陶瓷的制备及其介电性研究

为研究铋层状钙钛矿结构(Aurivillius相)铁电陶瓷居里温度(Tc)及介电性能,采用传统固相反应法在1 100℃烧结5 h制备了不同价态元素K~+、Ba~(2+)、Y~(3+)协同置换A位Sr元素的Sr_(1-x)(YK)_(0.25x)Ba_(0.5x)Bi_4Ti_4O_(15)陶瓷,利用X射线衍射仪表征不同置换量陶瓷的物相,结果表明制备的陶瓷均为Aurivillius相,无杂相产生。采用精密阻抗分析仪测量了陶瓷在不同频率下的介电温谱,结果表明,所有陶瓷样品均表现出铁电相变,随替换量增多,陶瓷的居里温度T_c由518.2℃降低到514.5℃,T_c处的介电常数极大值由2 350下降到2 000。研究结果表明,表征结构失稳性的容忍因子参数对Sr_(1-x)(YK)_(0.25x)Ba_(0.5x)Bi_4Ti_4O_(15)陶瓷铁电相变有重要影响。     

La1-xZnxMnO3和La2/3Sr_((1-x)/3)Znx/3MnO3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-xZnxMnO3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     

A位无序掺杂锰氧化物La2/3-xYxCa1/3-ySryMnO3的微结构和居里温度研究

采用固相反应法制备了A位无序掺杂锰氧化物La2/3-xYxCa1/3-ySryMnO3系列样品;利用Rigaku Dmax-rB 12 kW转靶X-ray衍射仪和振动样品磁强计Lakeshore7300对样品进行表征,并通过Rietveld方法对X-ray衍射谱进行结构精修。讨论了A位掺杂无序度σ2对样品的相、微结构（Mn—O键长、Mn—O—Mn键角等参数）和居里温度的影响。结果表明：随着掺杂浓度x和无序度σ2的增加,样品仍然保持单相性较好的钙钛矿正交结构,晶格常数a,b,c和晶胞体积V没有发生大的变化;Mn—O—Mn键角增加和Mn O键长减小;样品的居里温度下降,但x=0.20时,La2/3-xYxCa1/3-ySryMnO3居里点反而拉伸增大。     

制备氧压对外延锆钛酸铅铁电膜疲劳行为的影响

:利用脉冲激光沉积方法 ,在外延的具有钙钛矿结构的 La0 .35 Nd0 .35 Sr0 .3Mn O3导电膜上生长外延的铁电薄膜 Pb( Zr0 .5 2 Ti0 .48) O3。通过改变制备氧压控制铁电膜中氧的空穴浓度 ,研究其对 Pt/ Pb( Zr0 .5 2 Ti0 .48) O3/La0 .35 Nd0 .35 Sr0 .3Mn O3铁电电容器疲劳行为的影响     

Enhancement of magnetic properties and thermal stability of nanocrystalline （NdDyTb）12.3（FeZrNbCu）81.7B6.0 alloy with Co substitution

The major drawbacks of Nd-Fe-B magnets are relatively low Curie temperature and poor thermal stability. Ribbons with the near stoichiometric 2:14:1 composition of Nd_(10.8)Dy_(0.75)Tb_(0.75)Fe_(79.7-x)Co_xZr_(0.8)Nb_(0.8)Cu_(0.4)B_(6.0)(x=0, 3, 6, 9, 12, 15) were prepared by rapid quenching and subsequent heat treatment. The effect of Co element on the magnetic properties, thermal stability, and microstructure of the ribbons was systematically studied by vibrating sample magnetometer(VSM), thermal magnetic analysis, atomic force microscopy (AFM), and transmission electron microscopy (TEM).It was found that Co substitution was significantly effective in improving the magnetic properties and the thermal stability of nanocrystalline ribbons. Although the intrinsic coercivity decreased from 1308.7 kA/m for x=0 to 817.4 kA/m for x=15, the remanence polarization and maximum energy product increased from 0.839 T and 116.5 kJ/m~3 for the Co-free samples to 1.041 T and 155.1 kJ/m~3 for the 12at% Co-substituted samples,respectively.About 10 K increase in Curie temperature was observed for the 2:14:1 phase with lat% Co substitution. The absolute values of temperature coefficients of induction and coercivity were significantly decreased with Co substitution, which may be attractive for high operational temperature applications. The microstructure of nanocrystalline ribbons was slightly refined with Co substitution.     

Effect of Pb Substitution on the Microstructure and Ferroelectric Properties of Ba0.7Sr0.3TiO3 Ceramic

Ferroelectric Ba0.7Sr0.3TiO3(BST) and partially Pb2+ substituted for Ba2+ ceramics (Bao.7-xPbx)Sr0.3TiO3 (x=0.1-0.4,BPST) were prepared by using conventional solid-reaction method.XRD analysis shows that the samples microstructure changes from cubic phase to tetragonal one with the Pb2+ content increasing.ESEM analysis shows that the Pb2+ substituted samples have a denser and more uniform surface morphology than that of pure BST.Measured electrical properties suggest that the Pb2+ substitution for Ba2+ in the BST system enhances the ferroelectric performance obviously when x=0.2.In addition,the substitution increases the samples Curie temperature (Tc).(Ba0.5Pb0.2)Sr0.3TiO3 ceramic has good ferroelectric properties measured at a maximal electric field of 30 kV/cm under the condition of room temperature.The corresponding saturated polarization (Ps),remnant polarization (Pr) and coercive field (Ec) is respectively 15.687 μC/cm2,8.100μ C/cm2 and 6.611 kV/cm.The measured Tc of (Ba0.5Pb0.2)Sr0.3TiO3 is 117 ℃.     

（Dy_（0．65）Tb_（0．25）Pr_（0．1））_2（Fe_（1－x）A

报道了（Ｄｙ０．６５Ｔｂ０．２５Ｐｒ０．１）２（Ｆｅ１－ｘＡｌｘ）１７赝二元化合物的结构及居里温度随合Ａｌ量变化的一些观测结果，并运用Ｘ射线衍射强度理论，计算了该种化合物的衍射强度，确定了Ａｌ原子在晶体中所占的晶位，由此，定性地说明了居里温度升高的原因。     

Sr2Bi4-xLaxTi5O18铁电陶瓷性能的研究

采用固相烧结工艺制备了Sr2Bi4-xLaxTi5O18(x=0.00,0.10,0.25,0.50,0.75,1.00)陶瓷样品。用X射线衍射仪对其微结构进行了分析，并测量了其铁电、介电性能、。结果表明，随着La含量的增加，样品的剩余极化Pr和矫顽场Ec逐渐减小，这是由于La掺杂使得样品晶格畸变变小，从而导致剩余极化的降低。相变温度Tc随着La含量的增加而降低，这也与样品晶格畸变有关。     

Magnetic properties of Fe3（1-x）Cr3xC alloys

The magnetic properties of Fe33(1-x)Cr3xC alloys with x=0.05, 0.1, 0.15, and 0.2, which crystallize in the cementiteFe3C-type structure with space group Pnma, were investigated by means of magnetization measurements. These alloys show tem-perature-induced second-order magnetic phase transitions. The Curie temperature (Tc) of these alloys decreases with increasing x. The isothermal magnetic-entropy changes of these alloys were derived from the magnetic isotherms measured with increasing tem-x = 0.05 in a magnetic field change from 0 to 1 T and 0 to 5 T, respectively.     

Sr(Ba)_(1-X)La_XTiO_3(X=0.0,0.2)化合物的高温高压合成与XRD研究

本文首次采用高温高压固相反应法合成了Ｓｒ１－ＸＬａＸＴｉＯ３（Ｘ＝０．０，０．２）与Ｂａ１－ＸＬａＸＴｉＯ３（Ｘ＝０．０，０．２）样品，进行了Ｘ射线衍射谱ＸＲＤ测试．研究了稀土掺杂下高温高压合成规律及其结构性质，从高温高压极端条件合成这一领域为高温超导的研究打下了实验基础．