Tb0.4Dy0.6(Fe1-xMnx)1.91(x=0,0.05,0.1 0,0.15)合金的磁致伸缩性能

研究了Mn替代Fe对多晶Tb0.4Dy0.6Fe1.91合金棒材性能的影响.分析了Tb0.4Dy0.6(Fe1-xMnx)1.91(x=0,0.05,0.10,0.15)多晶棒材的结构、晶格常数、居里温度和磁致伸缩性能,发现Mn替代Fe后,样品仍然为MgCu2型Laves相结构.随着Mn含量从0增加到0.15,样品的晶格常数从7.335A增加到7.347A,居里温度从668K降低到526K.Mn原子的替代通过改变材料的交换相互作用、总磁矩和易磁化方向影响材料的磁致伸缩性能.实验结果显示,Tb0.4Dy0.6(Fe1-xMnx)1.91样品在石=0.10时综合性能最好.     

Dy2AlFe16-xMnx化合物的饱和磁化强度和居里温度

通过磁测量手段研究了Mn在Dy2AlFe16-xMnx(x=1,2,3,4,6,8)化合物中的磁行为及Mn替代对该化合物磁性的影响.研究结果表明Dy2AlFe16-xMnx化合物的饱和磁化强度Ms和居里温度Tc随Mn的替代量x的增大呈下降规律.分析认为Tc的这种下降是由于在Mn替代过程中,3d次晶格中交换作用的变化而引起的.     

MnFe1-xTixP0.77Ge0.23化合物的结构与磁性

利用高能球磨法和粉末烧结法制备了MnFe_1-xTi_xP_0.77Ge_0.23(x=0.03, 0.04, 0.06, 0.08, 0.09)系列化合物。室温X射线衍射结果表明化合物均呈现Fe₂P型六角结构,随着Ti含量的增加,晶格常数a、b减小,晶格常数c增大,晶胞体积有所增大。变温X射线衍射实验结果表明,MnFe_0.94Ti_0.06P_0.77Ge_0.23化合物在305～350 K温度区间内发生铁磁到顺磁的相转变,存在磁弹耦合现象。MnFe_1-xTi_xP_0.77Ge_0.23(x=0.03, 0.04, 0.06, 0.08, 0.09)化合物的磁性测量结果表明随着Ti含量增加化合物的居里温度降低,热滞变大,最大等温磁熵变减小。     

Pr0.15Tb0.30Dy0.55Fe1.85-xNix合金的磁性和磁致伸缩研究

用电弧炉熔炼得到Pr0.15Tb0.30 Dy0.55Fe1.85-xNix系列合金.通过X射线对合金进行结构分析,并拟合衍射峰得到晶格常数;样品的居里温度采用交流磁化率测量系统得到;磁化强度、磁致伸缩分别由振动样品磁强计和标准应变测试系统在室温下测量得到.实验表明所有的样品均呈现MgCu2型Laves相结构;随着Ni替代量的增加,样品晶格常数、居里温度和磁化强度呈现下降趋势;磁致伸缩系数亦表现为下降趋势,但在x=0.2、0.3处有所反弹,且x=0.3时样品在低场下的磁致伸缩值略高于无Ni替代的样品.     

纳米Dy0.15Fe1.85O3磁颗粒的低温磁特性研究

采用共沉淀–相转化法制备了纳米Dy0.15Fe1.85O3磁颗粒,研究了低温条件下温度变化对其磁学特性的影响.采用XRF、TEM、XRD和超导量子磁强计(SQUID)对样品的化学成份、形貌、晶型结构和磁学性能进行了表征.结果表明:样品中的金属离子主要是Dy3+、Fe3+,含量分别为12.17wt%、51.88wt%.形貌为类球形,平均粒径约15 nm,且结晶性完全,晶型为面心立方尖晶石结构.在56.5～200.2 K范围内,样品的饱和磁化强度(MS)、矫顽力(HC)均随温度的降低呈现出增大的变化规律,当温度T≥142.8 K时,呈超顺磁性状态;当T<142.8 K时,由超顺磁性状态转化为铁磁性状态.     

Bi1.5-xCaxZnNb1.5O7陶瓷结构、介电性能与结晶化学特性

采用固相反应法制备Bi1.5-xCaxZnNb1.5O7(0≤x≤0.50,BCZN)陶瓷,研究Ca2+替代Bi3+对Bi1.5ZnNb1.5O7陶瓷烧结特性、显微结构、介电性能和结晶化学特性的影响.结果表明:替代量x≤0.25 mol时,样品为单一的α-BZN相.随着Ca2+替代量增加,样品最佳烧结温度从1000℃升高到1020℃;致密度从7.011 g/cm3减小到6.353 g/cm3;样品晶粒尺寸、晶格常数、电阻率均减小;结晶化学参数键价和,AV(O’)[Bi4]、AV(O’)[Bi3Zn]、AV(O’)[Bi2Zn2]和AV(O’)[Ca3Zn]均增大,且该行为与其晶格常数、介电性能变化相吻合.     

双钙钛矿Sr2Fe1-xNixMoO6(x=0.0～0.4)化合物的制备及其结构的研究

采用溶胶-凝胶法成功地制备了双钙钛矿结构的Sr2Fe1-xNixMoO6(x=0.0～0.4)化合物.X射线衍射实验表明,Ni的掺入没有改变化合物的晶体结构和空间群,但晶格常数随Ni含量的增加而减小,同时B位阳离子的占位有序度随Ni含量的增多而增大.研究还表明,B位阳离子的占位有序度与样品的烧结温度也有很大的关系,烧结温度升高,有序度增大.扫描电镜分析表明,所制备的样品颗粒度均匀,界面清晰,Ni的掺入使颗粒细化.     

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。     

R2Fe17(R=Y,Tm)化合物的本征磁致伸缩随温度的变化

根据德拜理论和格律乃森关系导出的R2Fe17(R=Y,Tm)化合物在顺磁态的晶胞参数(a,c,v)及由负膨胀测定法得到的R2Fe17(R=Y,Tm)化合物的晶胞参数的差别,计算了R2Fe17(R=Y,Tm)化合物的本征体磁致伸缩随温度的变化关系.计算结果表明R2Fe17(R=Y,Tm)化合物的本征磁致伸缩随着温度的增加而急剧减小.分析表明这种现象与磁化强度和交换耦合作用随温度的下降有关.本文还研究了重稀土原子磁性对R2Fe17化合物的本征磁致伸缩的影响,结果表明重稀土原子磁矩及R-T交换耦合作用使R2Fe17化合物的本征磁致伸缩增强,但增强的幅度比3d次晶格引起的本征磁致伸缩小一个数量级,亦即R2Fe17化合物的本征磁致伸缩主要来源于3d次晶格中的Fe-Fe交换作用.     

溶胶-凝胶自燃法合成MnxZn 1-x Cu 0.2 Fe 1.8 O 4 纳米颗粒的结构和磁性

采用溶胶-凝胶自燃法制备了MnxZn1-xCu0.2Fe1．8O4（x=0．5，0．6，0．7，0．8，0．9）的粉末样品，并对样品在空气中500℃退火4h．XRD分析表明，所有的样品都具有单相尖晶石结构，不同Mn含量样品的平均颗粒尺寸在30-~40nm之间．XPS表明：退火前后，样品中大部分Mn以Mn^3＋形式存在；而Fe则在退火前以Fe^2＋和Fe^3＋混合价态存在，退火后以Fe^3＋形式存在．退火使表层的Mn和Fe所占的百分比都增大．用VSM常温下磁性的测量，发现退火样品的矫顽力（Hc）随Mn含量的增加陡峭地增大．未退火样品的Ms随颗粒中Mn含量的增加先增大后减小，x=0．8的样品有最大的Ms．退火对不同Mn含量样品的Ms影响不同．     

K2(Rb2,Cs2,Tl2)TeBr6(I6) and Rb3(Cs3)Sb2(Bi2)Br9(I9) perovskite compounds

We systematize available experimental data on the crystal structure of the ternary halides K₂(Rb₂,Cs₂,Tl₂)TeBr₆(I₆) and Rb₃(Cs₃)Sb₂(Bi₂)Br₉(I₉), analyze the general trends in the properties of their single crystals, and examine the key features of the physicochemical interaction in related systems.     

Flux growth of single magnetic sublattice antiferromagnetic garnets Ca3 Fe2 Ge3 O12 and Ca3 Mn2 Ge3 O12

Magnetic single crystals garnets Ca₃ X₂ Ge₃ O₁₂ with X = Mn³⁺ or Fe³⁺ containing Ca²⁺ and Ge⁴⁺ are of great interest due to the rise of an antifer-romagnetic order in one definite octahedral site. The optimal conditions for obtaining single magnetic-sublattice garnets of large size (1 cm in diameter) have been analyzed. Two groups of solvents have been tested: Bi₂ O₃ or PbO based flux. The best results were obtained with PbO flux and starting composition : % Moles 44 PbO 1b 35 GeO₂ 1b 15 CaO 1b 6 X₂ O₃.     

Syntheses and structures of Ta2(WO2)0.87H0.26(PO4)4 and Ta2(MoO2)(PO4)4

Tantalum hydrogen phosphate, β-TaH(PO₄)₂, has a three-dimensional structure that is stable to remarkably high temperature (∼600 °C) presumably due to the presence of strong hydrogen bonds. Impedance measurements indicate a low conductivity, 2.0 × 10⁻⁶ S/cm at 200 °C in 5% H₂. In further studies aimed at enhancing the conductivity by aliovalent doping, we have investigated systematically the synthesis of compounds in the TaH(PO₄)₂-W₂P₂O₁₁ system at 380 °C. As a result, a new phase, Ta₂(WO₂)_0.87H_0.26(PO₄)₄, was identified and subsequently the molybdenum analog Ta₂(MoO₂)(PO₄)₄ was also prepared. The structures were determined by single crystal X-ray diffraction techniques. The structures of Ta₂(WO₂)_0.87H_0.26(PO₄)₄ and Ta₂(MoO₂)(PO₄)₄ can be formally derived from the structure of β-TaH(PO₄)₂ by the replacement of two P-OH protons with an MO₂²⁺ (M = Mo and W) group together with a change in the orientation of some phosphate tetrahedra.     

(K0.44,Na0.52,Li0.04) (Nb0.84,Ta0.10,Sb0.06)O3 Ferroelectric Ceramics

Recent progress in (K_0.44,Na_0.52,Li_0.043-based ceramics (KNN) with special emphasis on (K_0.44,Na_0.52,Li_0.040.84,Ta_0.10,Sb_0.06))O₃ (KNN-LT-LS) is reviewed concisely. The base KNN and its compositional derivatives are analyzed in terms of dopant-property relationships, which are then extended to the ternary derivatives. The effects of processing conditions such as humidity, precursor purity, and oxygen partial pressure during sintering are elaborated on from a phenomenological perspective. It is also shown that the spontaneous polarization is sensitive to the processing route chosen for synthesis (mixed oxide versus perovskite routes). Special attention is devoted to the discussion of the morphotropic phase boundary (MPB) dilemma in the KNN-LT-LS system, where it is shown that the origin of high piezoelectric activity is actually due to a polymorphic transition at room temperature. It is shown that prototype transducers based on pure and 1 mol% Ba²⁺ doped KNN-LT-LS exhibit performance metrics comparable to those fabricated using PZT-5H. Overall, KNNLT- LS ceramics show great promise for lead-free applications, although issues such as temperature dependence of properties and strong sensitivity to processing conditions remain as the 2 major challenges.     

Preparation of (NH4)Zr2(PO4)3 and HZr2(PO4)3

(NH₄)Zr₂(PO₄)₃ has been prepared, hydrothermally, from α-zirconium phosphate in three different ways; (1) from amine intercalates at 300°C, (2) from mixtures of ZrOCl₂·8H₂O in excess (NH₄)H₂PO₄ and (3) reaction of NH₄Cl with Zr(NaPO₄)₂. Ammonium dizirconium triphosphate is rhombohedral with a = 8.676(1) and $\text{c}\text{= 24.288(5)}\text{A}\text{?}$. It decomposed on heating to HZr₂(PO₄)₃. Below 600°C a complex, as yet unindexed, X-ray pattern was obtained. A very similar X-ray pattern was obtained by washing LiTi_0.1Zr_1.9(PO₄)₃ with 0.3N HCl. Heating this phase or NH₄Zr₂(PO₄)₃, above 600°C resulted in the appearance of a rhombohedral phase of HZr₂(PO₄)₃ with cell dimensions a = 8.803(5) and $\text{c}\text{= 23.23(1)}\text{A}\text{?}$. The protons were not completely removed until about 1150°C. Decomposition of (NH₄)Zr₂(PO₄)₃ at 450°C yielded an acidic gas whereas at 700°C NH₃ was evolved. A possible explanation for this behavior is presented.     

Dielectric properties of Pb3 (PO4)2 | Pb3 (AsO4)2

The dielectric constants of Pb₃ (PO₄)₂ | Pb₃ (AsO₄)₂ at room temperature are intrinsic and fulfill the Lyddane - Teller - Sachs relation. At higher temperatures the specific conductivity increases with an activation energy of 0.56 eV leading to Maxwell - Wagner polarization effects thereby increasing the effective dielectric constant. Corresponding peaks in ∈' (T) are extrinsic and not attributed to structural phase transformations.     

Bi3(FeO4)(MoO4)2 and Bi3(GaO4)(MoO4)2 - new compounds with scheelite related structures

The title compounds have been prepared for the first time. They have monoclinic structures related to the scheelite (CaWO₄) structure, and they represent the first example of trivalent cations on tetrahedral sites of the scheelite structure. A superstructure is observed due to an ordering of the cations on the tetrahedral sites.     

Hydrothermal Crystallization in the Systems La2(CO3)3 ? 6H2O-CaCO3(BaCO3)-R-H2O (R = Na2CO3, K2CO3, NaHCO3, KHCO3, NaCl, NH4Cl, CO(NH2)2)

Crystallization in the systems La₂(CO₃)₃ ⋅ 6H₂O-CaCO₃(BaCO₃)-R-H₂O (R = Na₂CO₃, K₂CO₃, NaHCO₃, KHCO₃, NaCl, NH₄Cl, CO(NH₂)₂) was studied under hydrothermal conditions (400–450°C). The solid reaction products were found to contain LaOHCO₃ and NaLa(CO₃)₂. Detailed thermal decomposition schemes were proposed for these phases, and their lattice parameters were refined. __________ Translated from Neorganicheskie Materialy, Vol. 41, No. 11, 2005, pp. 1366–1372. Original Russian Text Copyright ? 2005 by Nikol'skaya, Dem'yanets.     

Direct observation of ferroelasticity in Pb3(PO4)2  Pb3(VO4)2

Ferroelasticity has been established in the room temperature phase of Pb₃(P_xV_1-xO₄)₂, (x ≥ 0.8). The coercitive stress and the spontaneous strain have been determined and found to be 1.6 bars and ca. 3.5 · 10^?4 respectively. The effect of domain switching on double refraction and Raman spectra is clearly brought out.     

Crystal Structure of (H3O)6[(UO2)5(SeO4)8(H2O)5](H2O)5

Crystals of (H₃O)₆[(UO₂)₅(SeO₄)₈(H₂O)₅](H₂O)₅ were prepared from aqueous solutions by evaporation. The crystal structure [monoclinic system, space group P2₁/m, a = 13.835(2), b = 13.4374(16), c = 14.310(3) Å, β = 108.004(14)°, V = 2530.1(7) Å ³] was solved by the direct method and refined to R ₁ = 0.090 for 4409 reflections with |F _hkl ≥ 4σ|F _hkl |. The structure is based on [(UO₂)₅(SeO₄)₈(H₂O)₅]⁶⁻ layers arranged parallel to the (101) plane; these layers have a unique topological structure. The U(1)O₆(H₂O) and U(3)O₆(H₂O) linked through selenate groups form chains running along [ [`1]\bar 1 01] direction. The chains are combined in layers by U(2)O₆(H₂O) bipyramids. The layers are linked with each other by hydrogen bonds through the H₂O and H₃O⁺ groups located between the layers.