K2Ln(NO3)5·2H2O(Ln=La,Ce,Pr,Nd,Sm)的晶体生长和热重-差热分析研究

本文生长出了K₂Ln（NO₃）₅·2H₂O（Ln=La；Ce；Pr；Nd；Sm）的单晶，并对其进行了晶体结构及差热-热重分析研究．结果表明，K₂Ln（NO₃）₅.2H₂O（Ln=La；Ce；Pr；Nd）的晶体属正交晶系，Fdd2空间群．首次生长出KPrN单晶并用直接法解出其晶体结构．解得KPrN的晶胞参数为：a=11．2210（10）A, b=21．411（3）A，c=12．208（2）A,Z=6；R=0．0240．对KLnN加热，则依次出现脱水、熔化、不可逆相变和NO的分解过程（K₂Ce（NO₃）₅·2H₂O除外）K₂Ln（NO₃）₅·2H₂O（Ln＝La；Nd；Sm）的NO分三步分解，K₂Ln（NO₃）₅·2H₂O（Ln=Ce；Pr）的NO分两步分解·KNO₃和Ln（NO₃）₃·nH₂O的混合物在225℃左右生成K₂Ln（NO₃）₅     

复合氧化物Ln0.67Sr0.33MnO3（Ln=La,Pr,Nd,Sm）的制备,结构与电性

本语文通过共沉淀工艺合成了复合氧化物Ｌｎ０．６７Ｓｒ０．３３ＭｎＯ３（Ｌｎ＝Ｌａ、Ｐｒ、Ｎｄ、Ｓｍ）与传统陶瓷制备方法相比，成相温度降低约４５０℃，经Ｘ射线衍射分析表明，所得复合氧化物为立方钙钛矿结构，晶胞参数随稀土离子半径变化而呈规律性变化，样品的四极法电阻率测试结果表明；样品中的稀土离子Ｌｎ的离子半径对其本身的地电性起决定性的作用，应用双交换理论，样品中的稀土离子Ｌｎ的离子半径对其本身的导电性     

固体燃料电池阴极材料La0.6Sr0.4Co0.2Fe0.8O3-δ的微观结构与阻抗特性研究

复合钙钛矿氧化物La_1-xSr_xCo_1-yFe_yO_3-δ是一种适于中温固体氧化物燃料电池的阴极材料. 采用柠檬酸螯合法合成了La_0.6Sr_0.4Co_0.2Fe_0.8O_3-δ粉体, 并通过XRD和SEM, 研究了前驱体溶液pH值和煅烧温度对其粉体晶相结构的影响; 同时, 通过烧结体的SEM和交流阻抗分析, 详细讨论了前驱体溶液pH值和烧结温度对烧结体显微结构和阻抗特性的影响. 结果表明, 前驱体溶液pH=4、煅烧温度为900℃的粉体, 1400℃下烧结2h获得的烧结体, 具有最低的阻抗.     

Ca0.3(Li1/2Sm1/2)0.7TiO3微波介质陶瓷的低温烧结研究

采用传统陶瓷制备工艺, 制备了掺杂Na₂O-CaO-B₂O₃(NCB)氧化物的Ca_0.3(Li_1/2Sm_1/2)_0.7TiO₃(CLST)陶瓷, 研究了NCB掺杂量与晶相组成、显微结构、烧结性能及微波介电性能的关系. 研究结果表明: 复合氧化物NCB掺杂量在1wt%～15wt%范围内没有杂相生成, 晶相仍呈斜方钙钛矿结构. 随着NCB添加量的增加, 陶瓷致密化温度和饱和体积密度降低, 介电常数ε_r、无载品质因数与谐振频率乘积Qf值也呈下降趋势, 频率温度系数τ_f向正方向增大. NCB氧化物掺杂能有效地将CLST陶瓷的烧结温度由1300℃降低至900℃. 添加12.5wt% NCB的CLST陶瓷在低温900℃烧结5h仍具有良好的微波介电性能: ε_r=73.7, Qf=1583GHz, τ_f=140.1×10-6/℃, 满足高介多层微波器件的设计要求.     

激光辐照引起Ge2Sb2Te5非晶态薄膜的电/光性质变化

研究了激光辐照引起Ge₂Sb₂Te₅非晶态薄膜的电/光性质变化, 当激光功率为580mW时薄膜的方块电阻有四个数量级(10⁷～10³Ω/□)的突变; 对电阻发生突变前、中、后的三个样品进行了XRD测试, 结果表明, 随着激光功率的增大,薄膜由非晶态向晶态转变,用椭偏仪测试了结构转变前、中、后三个样品的光学常数, 在可见光范围内薄膜的光学常数在波长相同情况下有: n_非晶态>n_中间态>n_晶态, k_晶态>k_中间态>k_非晶态, α_晶态>α_中间态>α_非晶态, 结合电阻变化曲线和XRD图谱讨论了激光辐照Ge₂Sb₂Te₅非晶态薄膜的电/光性质变化同激光功率和结构转变之间的关系.     

La2/3Sr1/3MnO3/ZnO混合物薄膜的磁电阻和伏安特性研究

利用脉冲激光沉积的方法在Si（100）氧化成SiO₂的基片上制备了(La_2/3Sr_1/3MnO₃)_x/(ZnO)_1-x混合物薄膜,研究了薄膜的磁电阻和伏安特性. X射线衍射分析表明,除了衬底SiO₂的衍射峰以外,分别出现了La_2/3Sr_1/3MnO₃（101）的衍射峰和ZnO（002）的衍射峰,且它们形成了两相共存体系. 实验表明：x=0.3的混合物薄膜表现为半导体导电特性,而x=0.4的样品则出现了典型的金属绝缘相变. 所制备的样品表现出了低场磁电阻效应和非线性伏安特性. 在0.7T磁场的作用下,x=0.3的样品在温度为60K时取得的最大磁电阻值为28.8%. 通过对伏安关系拟合表明,在La_2/3Sr_1/3MnO₃和ZnO颗粒之间存在一定的耗尽层,且产生了界面缺陷态.     

掺铒 Bi2O3-GeO2-Ga2O3-Na2O玻璃中激发态吸收的抑制

对应用于1.55μm波段宽带放大的掺Er³⁺:Bi₂O₃-GeO₂-Ga₂O₃-Na₂O玻璃中激发态吸收的抑制进行了研究. 为此, 在该玻璃中分别引入了Ce³⁺离子和B₂O₃组分. 研究表明, 随着玻璃中Ce₂O₃的掺杂或B₂O₃组分的引入, Er³⁺:⁴I_11/2能级与Ce³⁺:²F_5/2能级间的能量传递或Er³⁺:⁴I_11/2→⁴I_13/2能级间多声子弛豫速率相应提高, Er ³⁺离子⁴I_11/2能级荧光寿命显著减小, 激发态吸收得到有效抑制. 同时, 实验发现, Ce₂O₃的掺杂进一步提高了Er ³⁺离子⁴I_13/2→⁴I_15/2能级间总量子效率, 增强了1.55mum波段荧光发射强度, 而荧光发射谱宽基本保持不变. B2O3组分的引入虽在一定程度上削弱了1.55μm波段荧光发射强度, 但进一步拓展了其荧光发射谱, 且增益截面峰值波长移向长波段.     

(K0.5Na0.5)1-2xSrx(Nb0.94 Sb0.06)O3无铅压电陶瓷结构及性能研究

以传统电子陶瓷工艺制备了(K_0.5Na_0.5)_1-2xSr_x(Nb_0.94 Sb_0.06)O₃ 无铅压电陶瓷,研究了适量锶、锑取代对陶瓷结构及电性能的影响. 结果表明,少量的锶、锑取代没有改变(K_0.5Na_0.5) NbO₃陶瓷的相结构,仍为单相正交结构的钙钛矿型铁电体;适量的锶取代使得晶粒大小均匀一致,提高了陶瓷的致密度;锶、锑取代降低了陶瓷的居里温度,但对正交四方相变温度的影响不大,且在0~200℃的温度范围,介电常数几乎不依赖频率的变化而变化;在x=0.008处,得到较好综合性能的陶瓷材料：d₃₃=155pC/N,k_p=0.361,Q_m=120,N_p=2862,P_r=23μC/cm²,E_c=1.4kV/mm,ρ=4.411g/cm³.     

V5+取代对 Mg4(SbNb1-xVx)O9陶瓷介电性能的影响

研究了不同V⁵⁺含量Mg₄(SbNb_1-xV_x)O₉[MSNV, 0.05≤ x≤0.3]系陶瓷的烧结特性、微观结构和微波介电性能. 结果表明: 一定量V⁵⁺取代能够明显降低该陶瓷的烧结温度. 在所有组成范围内, XRD显示了单一刚玉型结构. 随V⁵⁺含量的增加, 样品的介电常数ε和品质因数Q·f先增大后减小, 样品的谐振频率温度系数τ_f逐渐减小, 这是由于V⁵⁺的取代使得B位键价增强所致. 在x=0.15, 1250℃烧结, 可获得ε_r=9.98, Q·f=20248GHz (8GHz), τ_f=-23.3×10-6·K^-1的新型微波介质陶瓷.     

不同气氛退火对多晶La0.9Ca0.1MnO3磁矩和比热的影响

对具有电脉冲诱发电阻可逆变化（EPIR）特性的多晶La_0.9Ca_0.1MnO₃在相同条件下经氩气和氧气退火后样品的磁矩和比热进行了研究.实验结果表明,经氧气退火后的磁矩和比热分别比氩气退火后的磁矩和比热增大.对氧气退火后的比热和氩气退火后的比热做差处理后发现,两种气氛退火后的比热差与T^3/2成线性关系.经氧气和氩气退火后的区别在于氧离子浓度的变化.经氧气退火后,氧离子浓度增加,导致样品中铁磁区域的增大,引起磁矩和比热增大.退火后磁矩和比热的变化与EPIR效应中磁矩和比热随电阻状态的变化趋势一致,表明EPIR效应与氧含量的变化有关.       

(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.     

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.     

Theoretical study of the insulating oxides and nitrides: SiO2, GeO2, Al2O3, Si3N4, and Ge3N4

An extensive theoretical study is performed for wide bandgap crystalline oxides and nitrides, namely, SiO₂, GeO₂, Al₂O₃, Si₃N₄, and Ge₃N₄. Their important polymorphs are considered which are for SiO₂: α-quartz, α- and β-cristobalite and stishovite, for GeO₂: α-quartz, and rutile, for Al₂O₃: α-phase, for Si₃N₄ and Ge₃N₄: α- and β-phases. This work constitutes a comprehensive account of both electronic structure and the elastic properties of these important insulating oxides and nitrides obtained with high accuracy based on density functional theory within the local density approximation. Two different norm-conserving ab initio pseudopotentials have been tested which agree in all respects with the only exception arising for the elastic properties of rutile GeO₂. The agreement with experimental values, when available, are seen to be highly satisfactory. The uniformity and the well convergence of this approach enables an unbiased assessment of important physical parameters within each material and among different insulating oxide and nitrides. The computed static electric susceptibilities are observed to display a strong correlation with their mass densities. There is a marked discrepancy between the considered oxides and nitrides with the latter having sudden increase of density of states away from the respective band edges. This is expected to give rise to excessive carrier scattering which can practically preclude bulk impact ionization process in Si₃N₄ and Ge₃N₄.     

Structure cristalline de Mn0, 4Er4, 6S7

The crystal structure of Mn₀, ₄Er₄, ₆S₇ ($\text{a}\text{= 12,573 (4)}\text{A}\text{?}$, $\text{b}\text{= 11,390 (4)}\text{A}\text{?}$, $\text{c}\text{= 3,777 (4)}\text{A}\text{?}$, γ = 105,45°, space group B2/m, Z = 2) has been refined by a least square method to a final R = 0,045, with 1431 independant reflections. The octahedral positions are occupied either by Er and Mn atoms or by Er atoms only and the prismatic sites by Er atoms.     

Effect of doping with Co2O3, TiO2, Fe2O3, and Mn2O3 on the properties of Ce0.8Gd0.2O2?δ

The effects of Co, Fe, Mn, and Ti oxide additions on the sinterability and crystal-chemical, thermal, and electrical properties of Ce_0.8Gd_0.2O_2−δ have been studied. The results indicate that these oxides enhance the sinterability of the mixed oxide, regardless of whether they were introduced before or after synthesis. The most effective sintering aid is Co₂O₃. The lattice parameters of Ce_0.8Gd_0.2O_2−δ samples containing different metal oxide additions (1 mol %) are refined in space group Fm3m. The temperature-dependent thermal expansion data are used to determine the linear thermal expansion coefficients of the samples. Manganese oxide additions reduce the electrical conductivity of Ce_0.8Gd_0.2O_2−δ, whereas the other dopants increase it in the order Ti < Fe < Co. The activation energy for conduction increases in the order Co < Ti < Fe < Mn. Original Russian Text ? E.Yu. Pikalova, A.N. Demina, A.K. Demin, A.A. Murashkina, V.E. Sopemikov, N.O. Esina, 2007, published in Neorganicheskie Material, 2007, Vol. 43, No. 7, pp. 830–837.     

Comparison of the Electronic Structures of La2CuO4, Sr2CuO2Cl2, and Sr2CuO2F2

First-principles cluster calculations are reported of the local electronic structure of the three compounds: La₂CuO₄, Sr₂CuO₂Cl₂, and Sr₂CuO₂F₂. The copper and the planar oxygen 2p atomic orbitals exhibit a similar degree of covalency. The out-of-plane orbitals, however, are quite different with the atomic orbital lowered significantly in energy for chlorine and fluorine apical positions.     

Structures cristallines de Sc3Cu4Ge4, T.R.3Cu4Sn4 (T.R. = Y,Gd, Tb,Dy, Ho,Er), isotypes de Gd3Cu4Ge4, et de la phase apparentee Tm3Cu4Sn4

Tm₃Cu₄Sn₄ has been studied by single - crystal X - ray diffraction analysis. The structure is of a new type with space group C2/m and Z = 2:a = 16.119(2), b = 4.3935(6), $\text{c}\text{= 6.896(1)}\text{A}\text{?}$, β = 115.88(2)°, D_x = 9.32 Mgm^?3, μ(MoKα) = 52 mm^?1, F(000) = 1045, R = 0.056 for 558 independant reflexions (R_w = 0.058). Tm₃Cu₄Sn₄ is a monoclinic distorded variety of the Gd₃Cu₄Ge₄ structure type. Seven other compounds were characterized: Sc₃Cu₄Ge₄ and R. E₃Cu₄Sn₄ where R.E. = Y, Gd, Tb, Dy, Ho, Er, isostructural with Gd₃Cu₄Sn₄.     

Magnetic properties of amorphous (fe, ni)80B20, (fe, ni)80B19si1, and (fe, ni)80P14B6alloys

Magnetic measurements were performed on amorphous (Fe, Ni)80B20, (Fe, Ni)80B19Si1, and (Fe, Ni)80P14B6alloy ribbons to yield the values of the magnetic moment per transition metal atom at 0 K and the Curie temperature. A close fit to the moment data, obtained by allowing not only the moments on Ni and Fe atoms to vary with Fe concentrationx, as revealed by neutron diffraction in crystalline alloys, but also the number of electrons per atom npand nbthat P and B atoms, respectively, donate to the transition metaldbands as described by the relationsn_{p} = 1.74 + 0.75 (1 - x)andn_{b} = 0.58 + 1.20 (1 - x), suggests a moment of 0 andsim0.13 mu_{B}per Ni atom in amorphous Ni80P14B6and Ni80B20alloys, respectively. The functional dependence of the Curie temperature onx, when followed closely for low Fe concentrations, gives the critical concentration xcabove which ferromagnetism appears in amorphous FexNi80-xB20and FexNi80-xP14B6alloy series asx_{c} cong 5and 8 at % Fe, respectively. The results of a theory based on coherent-potential approximation have been fitted to the measured values of Curie temperature in order to arrive at the Fe concentration dependence of the exchange interaction (JNiNi) between Ni-Ni pairs. The physical significance of the variation of JNiNiwithxobtained thereby has been discussed.     

Crystallization of sodium digermanate,Na2Ge2O5, from Na2O-GeO2 glasses

Na₂O-GeO₂ glasses containing 25～35 mole% Na₂O can be crystallized to give a new sodium germanate crystal together with Na₄Ge₉O₂₀, Na₂GeO₃ and/or Na₂Ge₄O₉ crystals. The new crystal is obtained as a principal crystallization product from the glass containing 33.3 mole% Na₂O, and is given a composition of Na₂Ge₂O₅. This sodium digermanate crystal is monoclinic with lattice parameters; a₀ = 8.421, b₀ = 4.962, c₀ = 12.67 Å and β = 103.5°, and isostructural with β-Na₂Si₂O₅. It is shown that the crystal is thermodynamically metastable.     

Preparation and characterization of NiO, Fe2O3, Ni0.04Zn0.96O and Fe0.03Zn0.97O nanoparticles

Nickel oxide (NiO), iron (III) oxide (Fe₂O₃), and mixed oxide (Ni_0.04Zn_0.96O and Fe_0.03Zn_0.97O) nanoparticles were synthesized by modified sol–gel method. The nanoparticle structural and morphological properties were investigated by infrared spectroscopy (FTIR), X-ray powder diffractometry (XRD), scanning electron microscopy (SEM), and Mössbauer spectroscopy. The mixed oxides were characterized by energy-dispersive X-ray spectroscopy (EDX). The oxide precursor powders were analyzed by thermogravimetry (TG) and differential scanning calorimetry (DSC). The average sizes of the obtained NiO and Ni_0.04Zn_0.96O nanocrystallites were evaluated by X-ray line broadening using Scherrer's equation and were found to be 36 and 23 nm, respectively. Fe₂O₃ and Fe_0.03Zn_0.97O nanoparticles presented similar sizes, around 19 nm. EDX spectroscopy indicated that the calculated compositions of the mixed oxides were nearly consistent with their estimated molar ratios.