共查询到20条相似文献,搜索用时 78 毫秒
1.
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 相似文献
2.
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 相似文献
3.
复合钙钛矿氧化物La1-xSrxCo1-yFeyO3-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La0.6Sr0.4Co0.2Fe0.8O3-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. 相似文献
4.
采用传统陶瓷制备工艺, 制备了掺杂Na2O-CaO-B2O3(NCB)氧化物的Ca0.3(Li1/2Sm1/2)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εr、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τf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: εr=73.7, Qf=1583GHz, τf=140.1×10-6/℃, 满足高介多层微波器件的设计要求. 相似文献
5.
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. 相似文献
6.
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(La2/3Sr1/3MnO3)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La2/3Sr1/3MnO3(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La2/3Sr1/3MnO3和ZnO颗粒之间存在一定的耗尽层,且产生了界面缺陷态. 相似文献
7.
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+:4I11/2能级与Ce3+:2F5/2能级间的能量传递或Er3+:4I11/2→4I13/2能级间多声子弛豫速率相应提高, Er 3+离子4I11/2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4I13/2→4I15/2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. 相似文献
8.
以传统电子陶瓷工艺制备了(K0.5Na0.5)1-2xSrx(Nb0.94 Sb0.06)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(K0.5Na0.5) 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,kp=0.361,Qm=120,Np=2862,Pr=23μC/cm2,Ec=1.4kV/mm,ρ=4.411g/cm3. 相似文献
9.
研究了不同V5+含量Mg4(SbNb1-xVx)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τf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εr=9.98, Q·f=20248GHz (8GHz), τf=-23.3×10-6·K-1的新型微波介质陶瓷. 相似文献
10.
对具有电脉冲诱发电阻可逆变化(EPIR)特性的多晶La0.9Ca0.1MnO3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T3/2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. 相似文献
11.
《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》2009,56(8):1586-1594
Recent progress in (K0.44,Na0.52,Li0.043-based ceramics (KNN) with special emphasis on (K0.44,Na0.52,Li0.040.84,Ta0.10,Sb0.06))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. 相似文献
12.
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. 相似文献
13.
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. 相似文献
14.
The crystal structure of Mn0, 4Er4, 6S7 (, , , 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. 相似文献
15.
E. Yu. Pikalova A. N. Demina A. K. Demin A. A. Murashkina V. E. Sopernikov N. O. Esina 《Inorganic Materials》2007,43(7):735-742
The effects of Co, Fe, Mn, and Ti oxide additions on the sinterability and crystal-chemical, thermal, and electrical properties
of Ce0.8Gd0.2O2−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 Ce0.8Gd0.2O2−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 Ce0.8Gd0.2O2−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. 相似文献
16.
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. 相似文献
17.
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), , β = 115.88(2)°, Dx = 9.32 Mgm?3, μ(MoKα) = 52 mm?1, F(000) = 1045, R = 0.056 for 558 independant reflexions (Rw = 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. 相似文献
18.
Magnetic measurements were performed on amorphous (Fe, Ni)80 B20 , (Fe, Ni)80 B19 Si1 , and (Fe, Ni)80 P14 B6 alloy 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 np and nb that P and B atoms, respectively, donate to the transition metald bands 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 Ni80 P14 B6 and Ni80 B20 alloys, respectively. The functional dependence of the Curie temperature onx , when followed closely for low Fe concentrations, gives the critical concentration xc above which ferromagnetism appears in amorphous Fex Ni80-x B20 and Fex Ni80-x P14 B6 alloy series asx_{c} cong 5 and 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 JNiNi withx obtained thereby has been discussed. 相似文献
19.
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. 相似文献
20.
D.M. Fernandes A.A. Winkler Hechenleitner M.F. Silva M.K. Lima P.R. Stival Bittencourt R. Silva M.A. Custdio Melo E.A. Gmez Pineda 《Materials Chemistry and Physics》2009,118(2-3):447-452
Nickel oxide (NiO), iron (III) oxide (Fe2O3), and mixed oxide (Ni0.04Zn0.96O and Fe0.03Zn0.97O) 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 Ni0.04Zn0.96O nanocrystallites were evaluated by X-ray line broadening using Scherrer's equation and were found to be 36 and 23 nm, respectively. Fe2O3 and Fe0.03Zn0.97O 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. 相似文献