Tb2AlFe16-x化合物的结构与磁性

通过X射线衍射魔磁测量手段研究了Tb2AlFe16-xMnx（x=1,2，3，4，5，6，7，8）化合物的结构与磁性。研究结果表明该化合物具有Th2Ni17型结构，随着Mn替代量工的增加，化合物的单胞体积V表现为先缓慢而后较快的线性增加，晶胞参数C单调递增，而α呈现复杂的变化．磁性质的研究结果表明随着工的增加，该化合物的居里温度及白发磁化强度开始急剧下降，后来下降变缓。这可能是与化合物中Mn磁矩反平行于Fe磁矩有关．     

Pr2AlFe16-xMnx化合物的反常热膨胀及磁性

通过X射线衍射及磁测量实验研究了Pr2AlFe16-xMnx化合物的结构与磁性,结果表明Pr2AlFe16-xMnx化合物具有Th2Zn17型结构;随着锰替代量的增加,化合物的单胞体积呈现先小后大的非线性增加,分析表明该类化合物在其磁相变点附近存在较大的正的本征磁致伸缩现象.进一步对Pr2A-1Fe13Mn3化合物进行的变温X射线衍射研究表明,该化合物在其居里点附近(180～198K)存在负热膨胀现象,其热膨胀系数为-3.6×10-4/K.磁性测量表明随着锰含量的增加Pr2A-lFe16-xMNX化合物的居里温度及自发磁化强度都急剧下降,对这些现象进行了解释.     

金属间化合物Tb(Fe1-xMnx)11.3Nb0.7的结构和磁性

研究了Mn部分替代TbFe11.3Nb0.7中的Fe对化合物结构和磁性的影响.利用真空电弧熔炼和真空热处理制备了Tb(Fe1-xMnx)11.3Nb0 7(x=0.05,0.10,0.15,0.20)化合物样品.粉末样品的X射线衍射和热磁曲线测量表明用Mn部分取代TbFe11.3Nb0.7中的Fe仍保持ThMn12型结构,且具有较好的单相性.晶格常数a和单胞体积V随Mn含量的增加而增大,但晶格常数c的增大比较平缓.所有这些化合物中都存在自发磁化现象,且其居里温度均≥300K.随着Mn含量的增加,化合物在4.4 K温度下的饱和磁化强度逐渐减小,平均每个Mn原子替代引起的饱和磁矩的降低约为3.4μB,过渡金属次晶格磁矩随Mn含量的增加也单调减小.     

La0.7-xNdxBa0.3MnO3纳米颗粒的居里温度与磁热效应

用溶胶-凝胶法制备了La0.7-xNdxBa0.3MnO3(x=0,0.05,0.10,0.15,0.20,0.25)多晶纳米颗粒,用XRD分析其相结构并计算晶格常数,用VSM测量样品的磁性能并计算磁熵变和居里温度.结果表明,La-Ba-Mn-O系列中适当的Nd掺杂可调整材料的居里温度至室温附近并有效提高其磁熵变.文中对于Nd掺杂对居里温度和磁熵变影响的机理进行了定性的分析.     

Tb2Fe17-xCrx化合物的结构与磁性

通过X射线衍射及磁测量手段研究了Tb2Fe17-xCrx（x=0、0．5、1．0、1．5、2．0、3．0)化合物的结构与磁性。研究结果表明Tb2Fe17-xCrx化合物具有Th2Ni17型结构，随着Cr替代量x的增加，Tb2Fe17-xCrx化合物的单胞体积呈现非线性的减小，而晶胞参数a、c呈现复杂的变化。分析表明Tb2Fe17-xCrx化合物中存在着较强的磁一弹耦合效应。对磁性质的研究结果表明随着Cr替代量x的增加，Tb2Fe17-xCrx化合物的居里温度升高，在x=1．0时达到最大值，为539K，当Cr替代量x继续增加时，Tb2Fe17-xCrx化合物的居里温度下降。随着Cr替代量x的增加，Tb2Fe17-xCrx化合物的自发磁化强度急剧下降，分析表明在Tb2Fe17-xCrx化合物中，Cr的磁矩反平行于Fe的磁矩。     

Nd2Co17-xMnx化合物的结构与磁性

研究了Nd2Co17-xMnx(x=0,1,3,5,7,9,11)化合物的结构和磁性，Nd2Co17-xMnx化合物具有菱方相Th2Zn17型结构；在x比较小时，随着x的增加，化合物的单胞体积缓慢增大，而在x比较大时，随着x的增加，化合物的单胞体积迅速增大，这表明Nd2Co17-xMnx化合物在磁性状态下存在着正的自发体磁致伸缩；随着x的增加，化合物的居里点及4.2K下的饱和磁化强度都快速下降，这表明在x比较小时，3d次晶格的Co-Co之间的铁磁变换作用起主导作用，而在x比较大时，3d次晶格中反铁磁交换作用起主要作用；在约234K观察到了Nd2Co14Mn3化合物的自旋重取向现象。     

影响巨磁电阻钙钛矿锰氧化合物居里温度的结构分析

测定了La1-xAx(MnB）O3型巨磁电阻钙钛矿化合物在不同组成时的居里温度，利用A位离子对晶格能的贡献和B位离子极化力的变化分别对A和B位离子掺杂及A，B位离子组成同时变化时钙钛矿的居里温度进行了分析，结果与实验一致。     

Nb对LaFe10.8-xNbxCo0.7Si1.5C0.2磁制冷合金成相和居里温度的影响

用真空电弧炉熔炼了LaFe10.8-xNbxCo0.7-Si1.5C0.2(x=0、0.01、0.07、0.10、0.14、0.36和0.74)合金,并对其铸态及退火态的显微组织、相成分及体积分数进行研究。结果表明,Nb的添加可细化铸态组织中的树枝晶,并促进退火过程中1∶13相的形成。其中当x=0.07时,铸态组织的细化作用最为明显,退火后可得到接近单一的1∶13相。差示扫描量热分析的结果表明,LaFe10.8-xNbxCo0.7Si1.5C0.2(x=0、0.01、0.07、0.10、0.14和0.36)合金在相变点附近发生了二级磁相变,且相变温度随Nb含量的增加呈先升后降的趋势。     

ZrO2和ZrO2:Dy3+纳米晶发光特性

采用液相沉淀法制备了不同掺杂浓度和尺寸的ZrO2和ZrO2Dy纳米晶,研究了其发光特性.结果表明在纳米ZrO2中,存在着宽带激发和发射,起源为电子在价带和导带之间的跃迁.在Dy3+掺杂的样品中,随着颗粒尺寸的长大,其发光增强.并且共掺杂Li+的样品发光强度被极大地提高.随着Dy3+浓度的变化,黄发射和蓝发射的强度比(Y/B)发生改变,且浓度猝灭是通过近邻激活剂间的交换作用进行的.     

RFe7Mn4Ti化合物的结构和磁性

利用真空电弧熔炼和真空热处理制备RFe7Mn4Ti(R=Y、Tb、Dy、Ho和Er)化合物样品。室温粉末样品的X射线衍射和热磁曲线测量表明：所有这些化合物都具有单ThMn12型结构．其晶格常数a、c和单胞体积V随着稀土元素的不同而变化。在DyFe7MmTi和HoFe7Mn4Ti化合物的热磁曲线上出现了明显的补偿特征．补偿温度分别约为123K和90K。本文还给出了这些化合物的居里温度和饱和磁化强度。     

Rapid preparation and characterization of Dy2Zr2O7 nanocrystals

Ultrafine fluorite type Dy₂Zr₂O₇ nanocrystals with cubic structure were fabricated at relatively low temperature by stearic acid method (SAM) using zirconium(IV) butoxide and dysprosium nitrate as raw materials, stearic acid as solvent and dispersant. The fabrication process was monitored by thermogravimetric analysis and differential thermal analysis (TG-DTA) and Fourier transform infrared spectroscopy (FT-IR). The obtained products were characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), energy dispersive X-ray spectrometer (EDS) and UV-vis absorption spectroscopy. A single phase of Dy₂Zr₂O₇ with high crystallinity was formed at 800 °C. The interplanar distances measured from the HRTEM image were 0.284 and 0.256 nm, respectively, coinciding with the theoretical values.     

Structural and electrical properties of HfO2/Dy2O3 gate stacks on Ge substrates

In the present work we report on the structural and electrical properties of metal-oxide-semiconductor (MOS) devices with HfO₂/Dy₂O₃ gate stack dielectrics, deposited by molecular beam deposition on p-type germanium (Ge) substrates. Structural characterization by means of high-resolution Transmission Electron Microscopy (TEM) and X-ray diffraction measurements demonstrate the nanocrystalline nature of the films. Moreover, the interpretation of the X-ray reflectivity measurements reveals the spontaneous growth of an ultrathin germanium oxide interfacial layer which was also confirmed by TEM. Subsequent electrical characterization measurements on Pt/HfO₂/Dy₂O₃/p-Ge MOS diodes show that a combination of a thin Dy₂O₃ buffer layer with a thicker HfO₂ on top can give very good results, such as equivalent oxide thickness values as low as 1.9 nm, low density of interfacial defects (2-5 × 10¹² eV^− 1 cm^− 2) and leakage currents with typical current density values around 15 nA/cm² at V_g = V_FB − 1V.     

Dy掺杂BaTiO3陶瓷的制备及其介电性能

采用溶胶凝胶法制备了掺杂不同量Dy2O3(掺杂摩尔分数分别为0.001,0.002,0.003,0.005,0.007)的BaTiO3陶瓷,并对其介电性能的变化进行了研究.结果表明Dy2O3掺杂使BaTiO3陶瓷的电阻率明显降低,当添加量为0.005mol时,电阻率最小,为4.19×108Ω·m.Dy2O3掺杂使BaTiO3陶瓷的介电性能在不同掺杂量和不同频率下发生了明显变化,掺杂量为0.001mol、0.002mol时,BaTiO3陶瓷的介电特性和频率特性得到明显改善,在频率为1000Hz时介电性能相对较好.Dy2O3掺杂使BaTiO3陶瓷的介电温谱有所展宽,且Curie温度有所降低,交流电导随着温度的升高而增大,并在Curie点附近达到最高.     

Phase equilibria and curie temperature in the LiNbO3−xTiO2 system,investigated by dta and x-ray diffraction

Solidus and liquidus temperatures, ferroelectric Curie temperature and lattice parameters of phases in the congruent LiNbO₃?xTiO₂ system was determined (0 < x < 0.465). The TiO₂ phase shows solid solubility in congruent LiNbO₃ up to x = 0.20 at 1187°C. The Curie temperature of the solid solution Li_0.954 Nb_1.0092 O₃:xTiO₂ decreases substantially with increasing amounts of TiO₂. This temperature variation was expressed as a function of the equivalent composition $\text{Re}\text{=}\text{0.954}\text{0.954 + 1.0092 +}\text{x}$; it coǐncides with the Curie temperature variation of LiNbO₃ with composition, which has also been studied by DTA. Outside the solid solution range (x > 0.20) two phases are present: a LiNbO₃ — type phase and a rutile-type phase.     

Ionic conductivity and crystallographic data for Na2-xCa1-xAlxSiO4 and Na2-xCaSi1-xPxO4 carnegieite phases

Single crystals of Na₂CaSiO₄ prepared at 30 kbar and 1500°C are cubic with $\text{a}\text{= 22.456}\text{A}\text{?}$. The polycrystalline compositions Na_1.9Ca_0.9Al_0.1SiO₄ and Na_1.8CaSi_0.8P_0.2O₄ can also be indexed using $\text{a}\text{= 22.458}\text{and}\text{22.471}\text{A}\text{?}$, respectively. The Ca carnegieites Na₂CaSiO₄, Na_1.9Ca_0.9Al_0.1SiO₄, and Na_1.8CaSi_0.8P_0.2O₄ have Na ion conductivities of only 5?8 × 10^?6 (ω-cm)^?1 at 300°C.     

Viscosity measurements in the system Dy2O3K2OMoO3

Crystals of DyKMo₂O₈ have been obtained as thick crystals or thin plates from melts containing K₂O.2MoO₃ and K₂O.3MoO₃ respectively. Viscosity measurements were made on two sets of these melt compositions in order to determine whether the habit changes were associated with changes in viscosity. By means of an oscillating crucible viscometer, similar viscosities in the range 1 to 6 cp were obtained between 1100°C and 500°C for both sets of compositions. This suggests that viscosity is not a factor affecting the change in crystal habit in this system.     

Thermodynamic properties of DyFeO3 and Dy3Fe5O12

A solid state electrochemical technique was employed to study the dissociation oxygen partial pressures of DyFeO₃ and Dy₃Fe₅O₁₂ at elevated temperatures. The standard enthalpies ΔH^o_f and entropies ΔS^o_f of formation were obtained to be - 1349.7 kJ/mol and - 253.2 J/mol·K for DyFeO₃ in the temperature range from 1173 to 1473 K, and - 4879.5 kJ/mol and - 1011.6 J/mol·K for Dy₃Fe₅O₁₂ in the temperature range from 1173 to 1523 K, respectively.     

Syntheses of hollandite type Rb2Cr8O16, K2Cr2V6O16 and K2V8O16

Hollandite-type compounds, Rb₂Cr₈O₁₆, K₂Cr₂V₆O₁₆ and K₂V₈O₁₆, were synthesized under high P-T conditions up to 1200°C and 7GPa. The structural refinement using a single crystal of Rb₂Cr₈O₁₆ confirms that the structure is similar to that of K₂Cr₈O₁₆. Magnetic measurements indicate that Rb₂Cr₈O₁₆ is ferromagnetic below 295K, K₂Cr₂V₆O₁₆ paramagnetic down to 77K and K₂V₈O₁₆ has susceptibility anomaly at 175K. These compounds are all semiconductive and show discontinuities in temperature-resistivity curves at points corresponding to magnetic anomalies.     

Studies on nonstoichiometry of Ca2MnxFe2−xO5+δ

The structure of Ca₂Mn_xFe_2?xO_5+δ (0 ≤ x ≤ 0.5), in which δ was determined by thermogravimetric and chemical analyses, was investigated by means of X-ray diffraction and Mo&#x030B;ssbauer effect measurements. Increase of δ was accompanied with increase of both tetravalent manganese ion and octahedral site and decreased the lattice parameter b_o. in the brownmillerite structure. Anomalous variation of the b_o with δ was explained to be due to the Jahn-Teller distortion caused by Mn³⁺. Above a certain value of δ, the brownmillerite phase changed into an ordered phase which has the lattice parameters a_o = a_dical, b_o = 2b_dical and C_o = 2C_dical. In the phase portion of iron ions was tetravalent.