多铁性材料Bi_(0.95)R_(0.05)(Fe_(0.95)Co_(0.05))O_3(R=La,Eu,Ho)的磁性及XAFS研究

利用溶胶-凝胶法成功制备双元素共掺杂Bi0.95R0.05(Fe0.95Co0.05)O3(R=La,Eu,Ho)系列样品。X射线衍射实验数据表明:Eu离子掺杂使得BiFeO3材料的晶体结构发生了变化。振动样品磁强计测量的样品磁性数据显示:La、Eu、Ho离子分别与Co离子共掺杂,能够提高样品铁磁性,而且Bi0.95Eu0.05(Fe0.95Co0.05)O3样品的铁磁性行为最明显。同步辐射X射线吸收精细结构实验结果说明:Eu离子掺杂改变了Fe原子的局域结构,使得Fe-O键长增加,影响了Fe3+-O-Co3+双交换作用,进而引起样品磁性的增强。     

双元共掺杂Bi1-xLax(Fe0.95Mn0.05)O3多铁性材料的磁性研究

采用溶胶-凝胶法制备了Bi1-xLax(Fe0.95Mn0.05)O3(x=0,0.10,0.15)多晶样品。X射线衍射实验表明La、Mn离子共掺杂没有改变样品的四方晶格结构。X射线能量色散分析显示样品的化学组分几乎不变。Mn离子掺杂或者是(La、Mn)离子共掺杂,导致铁酸铋材料的磁性增强。X射线吸收精细结构实验表明Mn3+的局域结构的改变是样品磁性增强的原因。     

多铁性材料Bi0.95R0.05(Fe0.95Mn0.05)O3(R=La,Pb)的磁性及局域结构研究

利用溶胶-凝胶法成功制备了共掺杂Bi0.95R0.05(Fe0.95 Mn0.05)O3(R=La,Pb)样品,并对样品的磁性进行了测量和研究.研究发现La掺杂的Bi(Fe0.95 Mn0.05)O3材料磁性有较大的提高,而Pb掺杂Bi(Fe0.95Mn0.05)O3样品的磁性减弱.同时,利用同步辐射实验技术对样品的局域结构进行了研究,进而分析样品磁性变化的原因.     

Bi0.9Ho0.1Fe0.95Cr0.05O3陶瓷制备及表征

采用传统固相反应法成功制备了Bi0.9Ho0.1Fe0.95Cr0.05O3(BHFCO)陶瓷。X射线衍射物相分析(XRD)表明,制备的BHFCO为纯相,具有菱方钙钛矿结构,属于R3c空间点群,晶格参数较块体BFO有所减小。介电常数与温度的关系曲线及差示扫描量热分析表明,BHFCO陶瓷具有明显介电弛豫特性,并在315℃附近存在反铁磁-顺磁相变。铁电测试表明BHFCO陶瓷具有饱和的室温电滞回线,剩余极化值为20.25μC/cm2。X射线光电子能谱分析(XPS)表明BHFCO陶瓷中Fe元素仅以Fe3+形式存在。磁性测试表明BHFCO陶瓷具有饱和的室温磁滞回线,饱和磁化场强为2.290A·m2/kg,剩余磁化强度为0.476A·m2/kg。     

巨磁电阻材料A0.05Co0.95Cr2S4(A=Zn、Ni、Cd、Fe)的输运行为及磁性能研究

过渡金属尖晶石型硫化物具有包括超巨磁电阻(CMR)效应在内的多种物理性能, 其CMR效应机理的研究对开发巨磁电阻材料有重要价值。目前, 铬基硫族尖晶石的CMR效应尚未深入研究。本论文通过固相反应法制备A_0.05Co_0.95Cr₂S₄(A=Zn、Ni、Cd、Fe)样品, 研究磁性和非磁性元素掺杂对CoCr₂S₄晶体结构和磁性能的影响。XRD检测表明, 掺杂的A_0.05Co_0.95Cr₂S₄(A=Zn、Ni、Cd、Fe)均呈现纯的尖晶石结构, 掺杂导致的晶胞参数变化与掺杂元素的离子半径成比例。磁电阻测定表明A_0.05Co_0.95Cr₂S₄(A=Zn、Ni、Fe)均具有巨磁电阻效应。掺杂削弱了铁磁相互作用, 导致A_0.05Co_0.95Cr₂S₄(A=Zn、Ni、Cd、Fe)的居里温度T_C降低。在0.01 T下, A_0.05Co_0.95Cr₂S₄(A=Zn、Ni、Cd、Fe)的零场冷却(ZFC)和加场冷却(FC)曲线均呈现磁性不可逆现象。A_0.05Co_0.95Cr₂S₄(A=Zn、Ni、Cd、Fe)呈现典型的亚铁磁性磁滞回线, 其中Zn_0.05Co_0.95Cr₂S₄的矫顽场最大。     

反相乳液界面合成中空Fe3O4/SiO2磁性微胶囊

报道了一种简单合成中空Fe3O4/SiO2磁性微胶囊的方法,即以反相乳液的水滴作为形成中空结构的软模板,通过界面溶胶-凝胶过程,制备中空Fe3O4/SiO2磁性微胶囊。利用扫描电子显微镜(SEM)、透射电子显微镜(TEM)、选区电子衍射(SAED)、多晶粉末X射线衍射(XRD)、傅里叶变换红外光谱(FTIR)及磁滞回线测量等手段对样品的结构和性质进行表征和研究。XRD、SAED和FTIR分析结果表明,微胶囊由SiO2和Fe3O4磁性纳米粒子(MPs)组成。SEM和TEM观察结果表明,微胶囊具有中空结构,且SiO2壳层具有多孔特性。磁性能检测结果表明,微胶囊具有超顺磁性和磁响应性。通过对比实验,提出SiO2界面异相成核的中空磁性微胶囊的形成机理。     

质子导体SrCe0.95Yb0.05O3-α溶胶凝胶燃烧合成的研究

综合利用溶胶凝胶及燃烧合成的优点制备了质子导体SrCe0.95Yb0.05O3-α粉体,发现柠檬酸的添加量是金属离子的2倍的情况下所制干凝胶燃烧时温度最高,合成产物最好;在燃烧合成中,柠檬酸作还原剂,而硝酸根离子作氧化剂;氧气不是燃烧反应的必要条件,但氧气可以加剧反应进行.XRD结果表明,1000℃即形成斜方钙钛矿结构,较高温固相反应合成温度降低了约400℃.     

化学镀法制备Ni/SrCe0.95 Yb0.05O3-α陶瓷基电极

本文采用化学镀法在陶瓷基SrCe0.95Yb0.05O3-α表面镀镍制备Ni/SrCe0.95Yb0.05O3-α陶瓷基电极,利用扫描电镜观察Ni电极的表面和截面形貌,用EDAX测定镀层的成分,并初步探讨了在陶瓷基上化学镀镍的工艺条件.结果发现采用HF:浓H2SO4:K2Cr2O7溶液(体积比)为1:1:3的粗化液以及用异丙醇作敏化剂所得镍层最好.     

(Mg0.95Ca0.05)TiO3晶体的激光加热基座法生长及其性质测定

采用激光加热基座法(LHPG)生长出了共晶系(Mg0.95Ca0.05)TiO3。晶体。通过粉末X射线衍射分析了所生长晶体的晶相，采用扫描电镜和显微拉曼光谱技术研究了所生长晶体的微观结构。(Mg0.95Ca0.05)TiO3晶体由CaTiO2和Mg-TiO2两种晶体复合而成。介电测量结果表明：(Mg0.95Ca0.05)TiO3晶体沿生长方向具有较大的介电常数和较小的共振频率温度系数。     

单相Bi_(0.95)La_(0.05)Fe_1-_xCo_xO_3陶瓷的多铁性能研究

利用高温高压技术制备了Bi_(0.95)La_(0.05)Fe_1-_xCo_xO_3(x=0,0.1,0.2)陶瓷样品。研究了La和Co共掺杂对BiFeO_3的物相结构及多铁性能的影响。结构分析表明,所有样品均为菱方钙钛矿结构,同时Co掺杂引起一定的结构畸变。Co掺杂导致Bi_(0.95)La_(0.05)FeO_3中空间调制的螺旋磁结构转变为共线的G型反铁磁结构,从而导致样品室温磁性能得到明显提高。样品中介电常数随着外加磁场的增加而增加,表明在Co掺杂Bi_(0.95)La_(0.05)FeO_3陶瓷中存在磁电耦合效应。在796 kA/m外加磁场及3k Hz频率下,Bi_(0.95)La_(0.05)Fe_(0.9)Co_(0.1)O_3和Bi_(0.95)La_(0.05)Fe(0.8)Co_(0.2)O_3的磁介电系数分别为1.61%和1.75%。     

Microstructure, electrical and optical characteristics of Mg(Zr0.05Ti0.95)O3 thin films grown on Si substrate by sol-gel method

Optical properties and microstructures of Mg(Zr_0.05Ti_0.95)O₃ thin films prepared by sol-gel method on n-type Si(100) substrates at different annealing temperatures have been investigated. The surface structural and morphological characteristics analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM) and atomic force microscope (AFM) were found to be sensitive to the deposition conditions, such as annealing temperature (600-800 °C). The optical transmittance spectra of the Mg(Zr_0.05Ti_0.95)O₃ thin films were measured by using UV-visible recording spectro-photometer. The diffraction pattern showed that the deposited films exhibited a polycrystalline microstructure. All films exhibited Mg(Zr_0.05Ti_0.95)O₃ peaks orientation perpendicular to the substrate surface and the grain size with the increase in the annealing temperature. The dependence of the microstructure and dielectric characteristics on annealing temperature was also investigated.     

Spin reorientation behavior and enhanced multiferroic properties of co-doped YFeO3 towards a monophasic multiferroic ceramic Co0.05Y0.95Fe0.95Ti0.05O3

Monophasic nanocrystalline lead-free relaxor ferroelectric samples of YFeO₃ and Co_0.05Y_0.95Fe_0.95Ti_0.05O₃ were prepared via the standard sol-gel synthesis method. The influence of Co and Ti co-doping on the structural, dielectric, ferroelectric, and magnetic properties were investigated using X-ray, Neutron Diffraction, Electric Polarisation, and magnetization measurement techniques. The structural analysis by the Rietveld method revealed an orthorhombic (Pnma) distorted perovskite structure. The analysis of the neutron diffraction data showed a spin reorientation from IR Γ4 to Γ2 in the doped sample. The universal dielectric response (UDR) phenomenon was used to explain the dielectric behavior. The temperature-dependent dielectric constant measurement shows a shift in the ferroelectric to paraelectric phase in Co_0.05Y_0.95Fe_0.95Ti_0.05O_3. The observed P-E loops indicate lossy ferroelectric nature for YFO and CYFTO. Enhancement in the value of saturation magnetization at room temperature was observed on co-doping. Furthermore, the presence of magnetodielectric coupling was established for the co-doped sample. Co-doping with Co and Ti in YFeO₃ enhanced the multiferroic properties of the pristine sample which may be helpful for future device applicability.     

Zn-Al共掺对0.95MgTiO3-0.05CaTiO3介电性能的影响

采用固相反应法制备了 (Mg_0.93Ca_0.05Zn_0.02)(Ti_1-xAl_x)O₃介质陶瓷.研究了Zn-Al共掺杂对0.95MgTiO₃-0.05CaTiO₃(95MCT)陶瓷介电性能的影响.结果表明：Zn-Al共掺杂的95MCT陶瓷的主晶相为MgTiO₃和CaTiO₃两相结构,Zn-Al共掺杂可以抑制中间相MgTi₂O₅的产生,同时,有第二相CaAl₂O₄出现;Zn-Al共掺杂能有效地降低95MCT陶瓷的烧结温度至1300℃,改善介电性能,并对介电常数温度系数具有调节作用.当 Zn²⁺掺杂量为0.02mol、Al³⁺掺杂量为0.02mol时, 在1300℃烧结2.5h获得最佳性能：ε_r =20.35, tgδ=2.0×106, α_c=1.78×106.     

Sr、Co共掺多铁性材料BiFeO3的性能

利用溶胶-凝胶法制备了BiFeO_3、Bi_(0.95)Sr_(0.05)FeO_3、BiFe_(0.95)Co_(0.05)O_3和Bi_(0.95)Sr_(0.05)Fe_(0.95)Co_(0.05)O_3样品,并对样品的结构、形态、元素含量、铁电性和铁磁性进行了研究。结果表明,共掺杂样品Bi_(0.95)Sr_(0.05)Fe_(0.95)Co_(0.05)O_3的晶体结构发生了变化,铁电性明显增强,但漏电流变大;Bi_(0.95)Sr_(0.05)FeO_3、BiFe_(0.95)Co_(0.05)O_3样品的磁性都有所增强,但Bi_(0.95)Sr_(0.05)Fe_(0.95)Co_(0.05)O_3样品的磁性并没有随着Sr和Co的共同掺杂而进一步提高,从氧空位浓度、Fe-O共价键结构的变化和晶体尺寸三个方面对产生这种现象的原因进行了分析。     

Synthesis,Structural, and Magnetic Properties of Nanocrystalline Ti 0.95Co0.05O2-Diluted Magnetic Semiconductors

With a view to investigate the influence of nanometric size on the structural, surface, and magnetic properties of nanocrystalline Ti_0.95Co_0.05O₂-diluted magnetic semiconductors, prepared by a novel simple controllable peroxide-assisted reflux chemical route followed by annealing at different temperatures, a systematic investigation has been undertaken. Structural characterizations such as X-ray diffraction followed by Rietveld refinement, electron diffraction pattern, Fourier transform infrared, Raman scattering, and X-ray photoelectron spectroscopy (XPS) measurements have shown anatase phase formation in nanocrystalline Ti_0.95Co_0.05O₂ without any additional impurity phases. The modified reflux chemical route was effective in obtaining pure phase Ti_0.95Co_0.05O₂ nanoparticles. Surface morphological investigations by using transmission electron microscopy and atomic force microscopy measurements showed the predominant effect of random distribution of nanoparticles on the aggregation behavior and local microstructural changes. The deconvoluted XPS core level Co 2p spectral study manifested the oxidation state of Co as + 2 and is found to be stable with varying particle size and annealing temperature. The ferromagnetic behavior was investigated by vibrating sample magnetometer, magnetic force microscopy, and electron spin resonance measurements. These magnetization studies showed all the samples are ferromagnetic at room temperature without any magnetic clusters. The correlation between structure, surface condition of the nanoparticles and local electronic interactions, and magnetization of the samples was analyzed and explored the origin of ferromagnetism.     

Irradiation induced texturing in the Mg0.95Mn0.05Fe2O4 ferrite thin film

We present a study on the effect of swift heavy ions irradiation on the structural and magnetic properties of Mg_0.95Mn_0.05Fe₂O₄ ferrite thin film grown by pulsed laser deposition technique. X-ray diffraction (XRD) pattern of the as-deposited film reveals a cubic spinel structure with an intermediate phase of α-Fe₂O₃. This impurity phase completely dissolves upon irradiation with 200 MeV Ag¹⁵⁺-ions and it exhibits a strong crystallographic texture along the (440) plane. The magnetization values start increasing systematically with irradiation at lower fluence values, whereas decrease for higher one. This decrease in magnetic signal can be attributed to partial amorphization caused by irradiation in agreement with XRD and atomic/magnetic force microscopic images.     

Novel multiferroic La0.95Sb0.05FeO3 orthoferrite

A series of La_1−xSb_xFeO₃ was prepared using the conventional solid state method. XRD revealed the formation of the orthorhombic structure with space group Pbnm. The data showed that, the molar magnetic susceptibility and coercive field H_C were increased from 9.16 × 10⁻³ to 26.9 × 10⁻³ emu g⁻¹ mol and 1196 to 5465 Oe from for LaFeO₃ to La_0.95Sb_0.05FeO₃, respectively. The coercive field (H_C) of the sample with x = 0.05 increased 6 times than that of the parent LaFeO₃ and the saturation magnetization (M_s) was increased from 0.1614 emu g⁻¹ for the parent LaFeO₃ to 0.2654 emu g⁻¹ for the doped sample_. The dielectric constant (?′) was increased with increasing the Sb³⁺ content. The ac conductivity (σ) increases from 2.36 × 10⁻³ Ω⁻¹ m⁻¹ for the LaFeO₃ to 30 × 10⁻³ Ω⁻¹ m⁻¹ for the sample La_0.95Sb_0.05FeO₃ at T = 553 K and frequency 1 MHz. The sample La_0.95Sb_0.05FeO₃ is concluded to be a novel single phase multiferroic material.     

Structural, magnetic and optical studies of (Zn0.90Co0.05Ni0.05O) DMS

ZnO DMS were prepared by co-precipitation method. Single phase Zn_0.90Co_0.05Ni_0.05O was confirmed by powder X-ray diffraction (XRD). The samples were characterized by EDS to confirm the expected stoichiometry. SEM revealed no surface precipitation of dopants. Photoluminescence for pure ZnO was observed in the bluish green region. Compared to undoped ZnO, the luminescence of Co-Ni co-doped ZnO was strongly quenched. The samples were examined for its magnetic property using vibrating sample magnetometer (VSM) which indicated ferromagnetic behavior at room temperature with a coercivity of 123.37 g. XRD measurements showed impurity phase for samples prepared by ceramic method.