不同离子掺杂对层状钙钛矿氧化物La_(1.3)Sr_(1.7)Mn_2O_7的影响

采用固相法制备了La_(1.3-x)R_xSr_(1.7)Mn_2O_7(R=Eu,Gd,Dy;x=0,0.1)系列样品,研究Ln位离子及离子半径对钙钛矿氧化物物性的影响.结果表明:由于Eu、Gd、Dy的半径依次减小,所以La_(1.2)Eu_(0.1)Sr_(1.7)Mn_2O_7、La_(1.2)Gd_(0.1)Sr_(1.7)Mn_2O_7和La_(1.2)Dy_(0.1)Sr_(1.7)Mn_2O_7的晶格失配度依次增大,导致3个样品的磁性、磁转变温度、MI转变温度依次减小乃至消失,电阻率随之增加.其结果归结于畸变引起强的电-声相互作用,导致双交换作用减弱,使样品的物性发生改变.     

BiFe_(0.9)Co_(0.1)O_3/Sr_3Co_2Fe_(24)O_(41)单层及双层复合十字空隙周期结构的微波吸收特性

采用时域有限差分(FDTD)法计算了具有十字空隙周期结构的单层BiFe_(0.9)Co_(0.1)O_3、Sr_3Co_2Fe_(24)O_(41)以及BiFe_(0.9)Co_(0.1)O_3/Sr_3Co_2Fe_(24)O_(41)双层复合材料的微波反射率,研究空隙尺寸对材料吸波性能的影响.结果表明,适当尺寸的周期性十字空隙结构能有效地提高材料的吸波效果.当十字形空隙的尺寸为长l=16mm,宽h=2mm时,BiFe_(0.9)Co_(0.1)O_3在频率15.8GHz位置的吸收峰峰值-23.2d B、-10d B频宽3.2GHz,Sr_3Co_2Fe_(24)O_(41)在频率15.2GHz位置的吸收峰峰值-42.5d B、-10d B频宽6.5GHz,BiFe_(0.9)Co_(0.1)O_3/Sr_3Co_2Fe_(24)O_(41)在频率16.1GHz位置的吸收峰峰值-63d B、-10d B频宽为4.3GHz.     

Nucleation and growth kinetics of La_(0.7)Sr_(0.3)Cr_(0.4)Mn_(0.6)O_(3-δ) SOFC perovskite:Symmetry alteration evolution induced by Cu~(2+) and Ni~(2+) impregnation

La_(0.7)Sr_(0.3)Cr_(0.4)Mn_(0.6)O_(3-δ) perovskite nanoparticles have been synthetized using an ethylene glycol modified solgel method and impregnated by Cu_(0.75)Ni_(0.25) nanoparticles. The phase transitions and nucleation kinetics were studied by time resolved x-ray diffraction, Rietveld, Raman spectroscopy and high resolution transmission electron microscopy. Findings have shown that, an atomic disorder dominates from room temperature to 400 °C. Nanoparticles with crystal size 26 nm start through nuclei formation of La_(0.7)Sr_(0.3)Cr_(0.4)Mn_(0.6)O_(3-δ) and SrCrO_4 solid solutions with Pm3m cubic and P2_1/n monoclinic symmetry respectively in the range of 600–650 °C. Symmetry reduction from the Pm3m→R3c space group had been obtained at a lower temperature(750 °C) than those reported in the literature in oxygen atmosphere and it was confirmed by an octahedral distortion, which takes place in the crystallographic direction[221]/(122). The Johnson-Mehl-Avrami model had described the whole process, where the existence of two phases was shown before it reached its complete D_(3d)~6 point group symmetry.     

Bi6Ti3Fe1.7Ni0.3O18陶瓷的改进固相法制备及性能表征

采用改进固相法制备c轴择优取向Bi_6Ti_3Fe_(1.7)Ni_(0.3)O_(18)陶瓷材料,重点研究Bi_6Ti_3Fe_(1.7)Ni_(0.3)O_(18)材料磁性能的各向异性及光吸收特性.X线衍射结果表明,由改进固相法制备的陶瓷样品均具有c轴择优取向,随着烧结温度的升高,样品的c轴择优取向度增加.磁性测试结果表明,所有样品面内的饱和磁化强度(Ms)均大于面外的饱和磁化强度.对光吸收性能的分析表明,Bi_6Ti_3Fe_(1.7)Ni_(0.3)O_(18)具有两条吸收边,对应的直接带隙分别为2. 01 e V和2. 44 e V.     

Na_(0.7)Ni_(0.5)Mn_(0.3)Fe_(0.2)O_2正极材料的制备及其储钠性能

为提升钠离子电池的储钠性能,采用溶胶-凝胶法合成了Na_(0.7)Ni_(0.5)Mn_(0.3)Fe_(0.2)O_2层状金属氧化物正极材料,并探讨了柠檬酸含量对材料形貌、结构和电化学性能的影响.形貌和结构分析表明,所得电极材料的成分主要为多晶Na_(0.7)Ni_(0.5)Mn_(0.3)Fe_(0.2)O_2,并伴有少量Ni O;随着柠檬酸含量的增加,Na_(0.7)Ni_(0.5)Mn_(0.3)Fe_(0.2)O_2的颗粒尺寸减小但团聚现象更加明显.电化学测试结果表明,当柠檬酸与金属氧化物的物质的量比为0.3∶1时,所得Na_(0.7)Ni_(0.5)Mn_(0.3)Fe_(0.2)O_2正极材料具有最优的电化学性能,其首圈放电比容量高达128.1 mA·h/g,经50次充放电循环后,仍能释放出91.6 mA·h/g的可逆比容量.此外,Na_(0.7)Ni_(0.5)Mn_(0.3)Fe_(0.2)O_2正极材料还拥有良好的倍率特性,在1.0 C高倍率下,其放电比容量可达84.4 m A·h/g,在快速充放电钠离子电池应用方面展现出良好的前景.     

双层钙钛矿锰氧化物(La_(0.9)Eu_(0.1))_(4/3)Sr_(5/3)Mn_2O_7的磁性和磁熵变研究

本文采用传统固相反应法制备多晶样品(La_(0.9)Eu_(0.1))_(4/3)Sr_(5/3)Mn_2O_7,并对其磁性和磁卡效应进行研究.研究表明:在低温部分出现反铁磁和铁磁相互竞争,在三维铁磁有序转变温度(T_c~(3D)≈75 K)至二维铁磁转变温度(T_c~(2D)≈227 K)范围内出现铁磁顺磁共存;此外,在T_c~(3D)附近,出现了较大的磁熵变,当外加磁场为1 T时其最大磁熵变值为1.69 J/(kg K),这表明该材料可能适合在液氢温区内作为一种磁制冷材料.     

(La0.7Sr0.3MnO3)(1-x)(CoFe2O4)x复合体中增强的室温磁电阻效应

利用溶胶-凝胶法制备了(La0.7Sr0.3Mn0.3)(1-x)(CoFe2O4)x复合体材料,并利用X射线衍射和57Fe的穆斯堡尔谱详细研究了其结构和微结构.利用超导量子磁强计测量了样品的磁性.结构和磁性的测量表明(La0.7Sr0.3MnO3)(1-x)(CoFe2O4)x复合体由La0.7Sr0.3MnO3和CoFe2O4组成,两相之间没有反应.复合体的电阻率随着CoFe2O4的加入而逐渐升高.在室温条件下5 kOe的磁场下得到了-5%的磁电阻效应,该值比同样品粒大小的纯La0.7Sr0.3MnO3样品的磁电阻效应大一倍.同时也比将非磁性的绝缘势垒如玻璃、CeO2等引入La0.7Sr0.3MnO3的室温磁电阻值大.表明一定量的铁磁性绝缘势垒的引入可以增强类钙钛矿锰氧化物的室温磁电阻效应.     

(La0.9Bi0.1)NiO3的制备及其热电性能

以硝酸盐为原料、柠檬酸为络合剂、无水乙醇为溶剂,采用溶胶-凝胶法获得(La0.9Bi0.1)NiO3的纳米前驱体,在800℃下煅烧该前驱体2 h得到单相的(La0.9Bi0.1)NiO3纳米级粉末.利用XRD、TG-DTA、SEM等手段对其结构进行表征,所得到的(La0.9Bi0.1)NiO3颗粒大约为50 nm.在空气气氛中1 000℃下烧结6 h获得多晶的(La0.9Bi0.1)NiO3陶瓷样品.对(La0.9Bi0.1)NiO3陶瓷材料的微观结构进行分析,并对其室温到700℃的热电性能进行研究.热电测试结果表明,(La0.9Bi0.1)NiO3是N型热电材料且具有一定的热电性能.     

Ba_(0.5)Sr_(0.5)Co_(0.8)Fe_(0.2)O_(3-δ)阴极材料制备与性能表征

凝胶浇注法制备了阴极材料Ba_(0.5)Sr_(0.5)Co_(0.8)Fe_(0.2)O_(3-δ),并对Ba_(0.5)Sr_(0.5)Co_(0.8)Fe_(0.2)O_(3-δ)材料的性能进行分析。制备的Ba_(0.5)Sr_(0.5)Co_(0.8)Fe_(0.2)O_(3-δ)为钙钛矿相,其颗粒粒度小,并且尺寸均匀。将粉末在1000℃下烧结,所得烧结体的孔隙率为29.86%。在500~800℃温度范围内测试,测试温度升高,电导率降低,在500℃时电导率最大为38.2 S/cm。阴极Ba_(0.5)Sr_(0.5)Co_(0.8)Fe_(0.2)O_(3-δ)与电解质Sm_(0.2)Ce_(0.8)O_(1.9)做成阴极对称单电池,在800℃时测得欧姆阻抗和界面阻抗分别为1.92Ω·cm~(-2)和0.17Ω·cm~(-2),阴极BSCF与电解质SDC的化学相容性好。     

Tb_(0.3)Dy_(0.7)(Fe_(0.9)T_(0.1))_(1.95)合金的结构、磁致伸缩和Mssbauer研究

系统研究了室温下Tb0.3Dy0.7(Fe0.9T0.1)1.95(T=Mn,Fe,Co,B,Al,Ga)合金中ⅢA族金属和过渡金属元素T替代Fe对晶体结构、磁致伸缩、内禀磁致伸缩、自旋重取向的影响.结果发现,不同金属T替代Fe,Tb0.3Dy0.7(Fe0.9T0.1)1.95合金具有相同的MgCu2型立方Laves相结构.ⅢA族金属B,Al,Ga替代使磁致伸缩λs下降幅度较大,同时发现Al,Ga替代使磁致伸缩容易饱和,表明Al,Ga替代可降低Tb0.3Dy0.7(Fe1?xTx)1.95合金的磁晶各向异性,而过渡金属Mn,Co替代Fe使Tb0.3Dy0.7(Fe1?xTx)1.95合金磁致伸缩λs下降幅度较小;不同替代金属元素,对内禀磁致伸缩λ111有不同的影响.M?ssbauer效应表明,Al,Ga替代使Tb0.3Dy0.7-(Fe0.9T0.1)1.95合金的易磁化方向在{110}面逐渐偏离了立方晶体的主对称轴,即自旋重取向,B,Mn,Co替代未使易磁化轴发生明显转动.     

铈锶复合六角铝酸盐(Ce(0.7)Sr_(0.3))MgA1_(11)O_(18.85)的合成及发光性质

本文报道一种新的紫外发光材料铈锶复合六角铝酸盐(Ce_(0.7)Sr_0.3)MgAl_(11)O_(18.85),它与SrAl_(12)O_(19)类质同晶,晶胞参数为:a=0.5590nm,c=2.203nm。与CeMgAl_(11)O_(19)比较,(Ce_(0.7)Sr_(0.8)MgAl_(11)O_(18.85)有更强的紫外发射效率。在该基质中,Ce~(3+)-Ce~(3+)之间能进行短程的能量迁移,迁移的步数大约为4～12。这种能量迁移可能是一种偶极一偶极相互作用。     

中温固体氧化物燃料电池双钙钛矿PrBaCo2O5+δ作为潜在阴极的电化学性能研究

通过溶胶-凝胶制备双钙钛矿PrBaCo_2O_(5+δ)(PBCO)中温固体氧化物燃料电池阴极材料,研究结果表明:PrBaCo_2O_(5+δ)为四方结构.在100~850℃内,PBCO样品为金属导电机制.交流阻抗谱的测试结果表明:PrBaCo_2O_(5+δ)电极在800℃时的极化电阻为0.034 8Ω·cm~2.采用La_(0.9)Sr_(0.1)Ga_(0.8)Mg_(0.2)O_(3-δ)(LSGM)电解质为支撑体的单电池在800℃时的功率密度达到558.7 m W/cm2.     

Evaluation of Ca3(Co,M)2O6 (M=Co, Fe, Mn, Ni) as new cathode materials for solid-oxide fuel cells

Series compounds Ca_3(Co_(0.9)M_(0.1))_2O_6(M = Co,Fe,Mn,Ni) with hexagonal crystal structure were prepared by sol-gel route as the cathode materials for solid oxide fuel cells(SOFCs).Effects of the varied atomic compositions on the structure,electrical conductivity,thermal expansion and electrochemical performance were systematically evaluated.Experimental results showed that the lattice parameters of Ca_3(Co_(0.9)Fe_(0.1))_2O_6and Ca_3(Co_(0.9)Mn_(0.1))_2O_6 were both expanded to certain degree.Electron-doping and hole-doping effects were expected in Ca_3(Co_(0.9)Mn_(0.1))_2O_6and Ca_3(Co_(0.9)Ni_(0.1))_2O_6 respectively according to the chemical states of constituent elements and thermal-activated behavior of electrical conductivity.Thermal expansion coefficients(TEC) of Ca_3(Co_(0.9)M_(0.1))_2O_6 were measured to be distributed around 16×10~(-6)K~(-1) and compositional elements of Fe,Mn,and Ni were especially beneficial for alleviation of the thermal expansion problem of cathode materials.By using Ca_3(Co_(0.9)M_(0.1))_2O_6 as the cathodes operated at 800 ℃,the interfacial area-specific resistance varied in the order of M = Co M = Fe M = Ni M = Mn,and the over-potential increased in the order of M = Fe ≈ M = Co M = Mn M = Ni.Among all of these compounds,Ca_3(Co_(0.9)Fe_(0.1))_2O_6 showed the best electrochemical performance and the power density as high as ca.500 mW cm~(-2) at800 ℃ achieved in the single cell with La_(0.8)Sr_(0.2)Ga_(0.83)Mg_(0.17)O_(2.815) as electrolyte and Ni-Ce_(0.8)Sm_(0.2)O_(1.9) as anode.Ca_3(Co_(0.9)M_(0.1))_2O_6(M = Co,Fe,Mn,Ni) can be used as the cost-effective cathode materials for SOFCs.     

钙钛矿型La0.1Sr0.9Co0.9Fe0.1O3-δ膜的非化学计量及氧渗透模型

钙钛矿型透氧膜的非化学计量平衡关系与氧分压和温度有关,并对其应用起决定作用.文中以金属硝酸盐为前驱体,采用EDTA-柠檬酸联合络合法制备了钙钛矿型氧化物La0.1Sr0.9Co0.9Fe0.1O3-δ,并利用TG/DSC、XRD、SEM等方法对La0.1Sr0.9Co0.9Fe0.1O3-δ粉体的晶体结构和表面形态进行了表征.温度在923~1 223K、压力在0.101~1.01×105Pa之间变化时,采用热重分析法测得La0.1Sr0.9Co0.9Fe0.1O3-δ的非化学计量值在0.33~0.51之间.文中还利用简化的半经验公式对非化学计量值δ进行了计算,发现半经验公式能很好地与实验数据相拟合,由此得到了一个氧渗透通量的计算模型.实验结果表明,所提出的模型能够较好地预测La0.1Sr0.9Co0.9Fe0.1O3-δ膜的氧渗透通量.     

Er3+掺杂0.5Ba(Zr0.2Ti0.8)O3-0.5(Ba0.7Ca0.3)TiO3压电陶瓷的性能研究

采用传统固相烧结方法制备了Er~(3+)掺杂0.5Ba(Ti_(0.8)Zr_(0.2))O_3-0.5(Ba_(0.7)Ca_(0.3))TiO_3无铅压电陶瓷.考察了不同浓度Er~(3+)离子掺杂对其晶体结构和上转化发光性能的影响.XRD实验结果表明制备出的陶瓷样品均为纯的钙钛矿结构,且形成三方相和四方相的准同型相界.在980 nm波长激发下,陶瓷显现出明显的上转化发光性能,有3个明显的Er~(3+)特征峰,分别位于528,550 nm处绿光发射和661 nm处红光发射;当Er~(3+)掺杂量x=0.015 mol时,上转换发光性能达到最佳.该材料属于一种光-电多功能材料,即既具有上转换发光性能又具有铁电/压电性能.稀土掺杂0.5Ba(Ti_(0.8)Zr_(0.2))O_3-0.5(Ba_(0.7)Ca_(0.3))TiO_3固溶体的发光性能可以通过电场来调控.     

Sr_(1-x)Ln_xFBiS_2(Ln=La,Ce)体系的超导电性

在新发现的SrFBiS_2体系掺杂稀土元素镧和铈,利用固相反应法成功合成出Sr_(0.5)Ln_(0.5)FBiS_2(Ln=La,Ce)多晶样品.通过X射线衍射、电阻和磁化强度测量,发现母体样品SrFBiS_2是一个半导体,通过La或者Ce掺杂后,Sr_(0.5)Ln_(0.5)FBiS_2(Ln=La,Ce)在2.8K展现出大块超导电性.同时,研究发现Sr_(0.5)Ce_(0.5)FBiS_2先在7.5K形成铁磁序,然后在2.8K进入超导态,是一个铁磁超导体.这些结果对研究BiS_2基超导机制以及铁磁与超导共存的内在联系具有重要意义.     

Tb0.3Dy0.7(Fe0.9T0.1)1.95合金的结构、磁致伸缩和M(o)ssbauer研究

系统研究了室温下Tb0.3Dy0.7(Fe0.9T0.1)1.95 (T = Mn, Fe, Co, B, Al, Ga)合金中ⅢA族金属和过渡金属元素T替代Fe对晶体结构、磁致伸缩、内禀磁致伸缩、自旋重取向的影响. 结果发现, 不同金属T替代Fe, Tb0.3Dy0.7(Fe0.9T0.1)1.95合金具有相同的MgCu2型立方Laves相结构. ⅢA族金属B, Al, Ga替代使磁致伸缩(s下降幅度较大, 同时发现Al, Ga替代使磁致伸缩容易饱和, 表明Al, Ga替代可降低 Tb0.3Dy0.7(Fe1-xTx)1.95合金的磁晶各向异性, 而过渡金属Mn, Co替代Fe使Tb0.3Dy0.7(Fe1-xTx)1.95合金磁致伸缩λs 下降幅度较小; 不同替代金属元素, 对内禀磁致伸缩(111有不同的影响. M(o)ssbauer 效应表明, Al, Ga 替代使 Tb0.3Dy0.7- (Fe0.9T0.1)1.95合金的易磁化方向在{110}面逐渐偏离了立方晶体的主对称轴, 即自旋重取向, B, Mn, Co替代未使易磁化轴发生明显转动.     

La_(0.5)Eu_(0.2)Sr_(0.3)MnO_3钙钛矿型锰氧化物的~(151)Eu穆斯堡尔效应

利用穆斯堡尔效应研究了A位La被Eu替代的锰氧化物La0.5Eu0.2Sr0.3MnO3和La0.4Eu0.3Sr0.3MnO3的磁性、导电性、磁电阻效应.一定比例的Eu掺杂能够使La0.7Sr0.3MnO3样品出现M-I转变.穆斯堡尔参数表明在250 K附近存在一种磁结构转变;高温区T＞260 K时,θD=120 K,低温区T＜360 K时,θD=260 K.     

La_(0.8)Sr_(0.2)Mn_(0.98-x)Fe_xCo_(0.02)O_3微波吸收特性研究

用溶胶-凝胶法制备La_(0.8)Sr_(0.2)Mn_(0.98-x)Fe_xCo_(0.02)O_3(x=0.08、0.10、0.12、0.14)晶粉,用场发射扫描电子显微镜和XRD表征其微观形貌和晶体结构,用微波网络矢量分析仪测量样品在2~18 GHz频率范围内的复介电常数和复磁导率,根据测量数据计算微波反射率与频率的关系曲线.研究结果表明:900℃煅烧3 h的La_(0.8)Sr_(0.2)Mn_(0.98-x)Fe_xCo_(0.02)O_3粉晶平均粒径约100 nm,晶体结构为钙钛矿型;在测试范围内,样品都有一个吸收峰,峰高及频率位置随x不同而异;厚度2 mm,x=0.08、0.10、0.14,大于10dB的吸收带宽达到4 GHz以上,样品既有介电损耗又有磁损耗,但介电损耗要大于磁损耗.     

烧结温度对PMSZT压电陶瓷相结构和机电性能的影响

采用固相合成法制备了三元系压电陶瓷Pb_(0.98)Sr_(0.02)(Mn_(1/3)Sb_(2/3)),(Zr_(0.5) Ti_(0.5)_(1-x)O_3(0相似文献