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1.
利用自行设计的介质阻挡放电型低温等离子体反应器,研究了NO初始浓度、O2初始浓度、放电功率、电源频率等因素对NTP转化N2/O2/NO气氛中NO的影响规律。研究发现,NO去除率随功率增大而升高,到达一最大值后随功率增大而降低;NO去除率随O2初始浓度增加而降低,随NO初始浓度增大而减小。相同放电功率下,同一组分中NO去除率随电源频率的增加而降低,因此相同放电功率下降低电源频率可提高NO去除率。O2初始浓度不高于5%时,NOx大部分为NO,NO2和O3浓度均随放电功率增大而降低,NO2、O3生成量随O2初始浓度升高而增多。  相似文献   

2.
研究了La2O3对Yb:Y2O3透明陶瓷光谱性能的影响,添加适量La2O3以后,Yb:Y2O3透明陶瓷的吸收峰和发射峰的位置不变,但由于La3+的离子半径大于Y3+的离子半径,在Y2O3中引入La3+离子后,导致Y2O3晶格常数变大,晶场强度变弱,同时降低了Y2O3晶体的有序度,致使发射峰强度有所下降,发射截面变小.过量的La2O3x=0.16)造成Yb3+激活离子发射强度明显下降;其荧光寿命在添加La2O3后总体增大45%—60%. 关键词: 氧化镧 氧化钇 透明陶瓷 光谱性能  相似文献   

3.
本文通过实验研究了CO2质量分数为11.39%~70.95%,壁面过冷度为5~25 K,总压力为5~15 kPa的CO2/H2O混合气体自然对流条件下在水平管外的凝结换热规律,结果表明CO2/H2O的凝结换热系数随CO2含量和壁面过冷度的增大而降低,但随总压力的增大而增大。根据实验结果建立了新关联式,将关联式应用到凝汽器的设计计算与分析,且对凝汽器进行了分离特性和经济性分析。  相似文献   

4.
利用正电子湮没实验,结合x射线衍射(XRD)结构分析,研究了具有混合稀土特征的(Y1 -xGdx)Ba2Cu3O7-δ系列样品. XRD 实验结果表明,半径较大的Gd离子Y位替代使得样品晶胞参数和晶胞体积增大,但所有样品 仍保持与YBa2Cu3O7-δ(YBCO)样品相同的单相正交结 构. 正电子湮没实验表明,正电子各寿命参数表现出很强的Gd替代依赖关系. 从正电子实验 结果出发,计算了Cu-O链区局域电子密度ne的变化. 结果表明,局域电子密度n e随Gd含量x的增加而减小,而超导转变温度Tc随局域电子密度ne的减小而增加,这种局域电子密度ne与超导电性的关联是与铜位替代 完全不同的,且可能是近年来人们关于混合稀土铜氧化物体系具有较高临界电流密度的原因 之一. 该研究结果为铜氧化物超导体的应用和机理研究提供了相应的正电子实验资料. 关键词: 超导电性 正电子湮没 相结构 局域电子密度  相似文献   

5.
本文研究了Pr_(0.2)Yb_(0.8-x)La_xBa_2Cu_3O_(7-δ)体系的晶体结构,超导电性和磁性。结果表明,在Pr含量不变的条件下,超导转变温度随稀土离子半径增大而降低,当x≈0.65时,Tc=0;电子比热和费密能级上的态密度也随稀土离子半径增大而降低。并讨论了稀土离子半径与杂化的关系。  相似文献   

6.
用固态反应法制备了RBa2Cu3O7δ(R123)系列样品,其中R=Tm,Dy,Gd,Eu,Nd和Y.利用正电子湮没技术以及x射线衍射等实验技术研究了稀土离子半径r对材料局域电子结构和晶体结构以及超导电性的影响.实验结果表明,正电子寿命参量τ1,τ2均随R3+半径增加而单调增加;据此所给出的局域电子密度ne,随稀土离子半径的增加表象出单调减小的趋势.实验证明局域电子密度以及晶格结构的正交性均是影响材料超导电性的因素 关键词: 稀土离子半径 高温超导电性 正电子湮没 局域电子结构  相似文献   

7.
曹效文  唐元冀  何健民 《物理学报》1994,43(11):1854-1859
系统地研究了R1-xPrxBa2Cu37-δ的超导Tc与Pr替代浓度x的关系。发现在离子半径ri≤ri(Dy)时,在低Pr浓度范围内存在一个超导Tc平台,并且平台宽度表明一个R3+离子尺寸效应。我们认为,Tc平台宽度的离子尺寸效应可能起源于Pr4f电子局域态的改变。提出一个临界R3+离子半径ric,ri>ric时RBa2Cu37-δ的超导电性消失 关键词:  相似文献   

8.
马立安  郑永安  魏朝晖  胡利勤  郭太良 《物理学报》2015,64(23):237901-237901
采用化学气相沉积法系统研究了合成温度和N2/O2流量对生长在碳纤维衬底上的SnO2纳米线形貌及场发射性能的影响规律. 利用扫描电镜(SEM)、透射电镜(TEM), X射线衍射(XRD)及能谱仪(EDS)对产物细致表征, 结果表明, SnO2纳米线长径比随反应温度的升高而增大; 随N2/O2流量比值的增大先增大后变小, 场发射测试表明, 合成温度780 ℃, N2/O2流量比为300 : 3 时SnO2纳米线阵列具有最佳的场发射性能, 开启电场为1.03 V/μm, 场强增加到1.68 V/μm时, 发射电流密度达0.66 mA/cm2, 亮度约2300 cd/m2.  相似文献   

9.
本文用X射线粉末法测定了Li2K(IO3)3与Li2NH4(IO3)3的晶体结构和原子参数。发现Li3K(IO3)3,Li2NH4(IO3)3与Li2Rb(IO3)3同晶型,属单斜晶系,空间群为P21/α,每个单胞含有四个化合式量。室温的点阵常数分别为α=11.198?,b=11.046?,c=8.254?,β=111.53°,及α=11.327?,b=11.078?,c=8.341?,β=111.87°。讨论了二元化合物的形成与离子半径的关系。 关键词:  相似文献   

10.
刘明  曹世勋  袁淑娟  康保娟  鲁波  张金仓 《物理学报》2013,62(14):147601-147601
利用固相反应法制备了Dy1-xPrxFeO3系列化合物. X射线粉末衍射晶体结构分析表明, 随着Pr掺杂量x的增加, 样品晶胞体积逐渐增大, 晶格畸变减弱. Raman光谱测量表明稀土离子有效质量[meff=xmPr+(1-x)mDy] 与晶格结构的变化共同导致该体系Raman光谱的变化. 随Pr掺杂量的增加, 波数小于200 cm-1的振动模式基本保持不变, 而波数大于200 cm-1的振动模式(除420 cm-1处的B3u模式外)向低频移动. 磁测量结果表明, 由Dzyaloshinsky-Moriya 相互作用导致的宏观磁性随Pr掺杂量增加逐渐减弱. 稀土离子与铁离子磁晶格的耦合作用以及晶格结构畸变的变化共同导致该体系自旋重取向相变温度在一定的掺杂量 (x=0.3)前后先升高后降低. 关键词: 稀土铁氧体 自旋重取向 晶体结构 Raman光谱  相似文献   

11.
Using electron spin resonance (ESR) technique we have obtained data evidencing the existence of magnetic vortices in high-temperature superconductors at temperatures above the critical one T c. We have studied magnetic excitations in Bi2Sr2Ca2Cu3O10 single crystals above T c with the method of surface spin decoration. The surface layer of diphenylpicrylhydrazyl was used as a sensitive probe of magnetic field distortions. The temperature dependence of the ESR signal parameters has indicated that far above T c the magnetic flux of a sample is affected by the superconducting order parameter fluctuations while close to T c its changes are due to vortex-type excitations.  相似文献   

12.
Single crystals of (Sn1-xErx)Er4Rh6Sn18 are superconducting (Tc = 1.3K) for x 0, are reetrant superconducting (Tc = 1.24K and TM = 0.34K) for x ~.30 and undergo a singel magnetic transition (TM=0.68K) for x~.75. Since the occupancy of the [Sn(1)1-xEr(1)x]Er(2)4 sublattice is responsible for the variation of the low-temperature properties, one can make predictions as to new reentrant superconductors in the MRhxSny series (M=RE). This appears to be the first system of reentrant superconductors where stoichiometry within a sublattice controls both magnetic ordering and superconductivity.  相似文献   

13.
The unit cell volume and phase transition temperature of LaFe11.4Al1.6Cx compounds have been studied. The magnetic entropy change, refrigerant capacity and the type of magnetic phase transition are investigated in detail for LaFe11.4Al1.6Cx with x=0.1, All the LaFe11.4Al1.6Cx (x=0-0.8) compounds have the cubic NaZn13-type structure. The addition of carbon atoms brings about a considerable increase in the lattice parameter. The bulk expansion results in the change of phase transition temperature (Tc), Tc increases from 187K to 269 K with x varying from 0.1 to 0.8, Meanwhile an increase in the lattice parameter can also cause a change of the magnetic ground state from antiferromagnetic to ferromagnetic. Large magnetic entropy change IASI is found over a large temperature range around Tc and the refrigerant capacity is about 322J/kg for LaFe11.4Al1.6C0.1. The magnetic phase transition belongs in weakly first-order one for x=0.1.  相似文献   

14.
研究了掺Ba对Bi2Sr2-xBaxCaCu2Oy(0≤x≤0.15,0.3)单晶和多晶样品超导电性的影响,结果表明,有少量Ba2+离子进入了超导相,且有固溶度极限.对于2212相单晶,c轴参数和Tc均随Ba含量增加而增加;对于慢冷多晶样品,掺Ba可明显提高Tc;然而对于淬大多晶样品,Tc没有明显变化,用掺Ba 关键词:  相似文献   

15.
We report the temperature dependence of susceptibility for various pressures, magnetic fields and constant magnetic field of 5 T with various pressures on La2−2xSr1+2xMn2O7 single crystal to understand the effectiveness of pressure and magnetic field in altering the magnetic properties. We find that the Curie temperature, Tc, increases under pressure (dTc/dP=10.9 K/GPa) and it indicates the enhancement of ferromagnetic phase under pressure up to 2 GPa. The magnetic field dependence of Tc is about 26 K for 3 T. The combined effect of pressure and constant magnetic field (5 T) shows dTc/dP=11.3 K/GPa and the peak structure is suppressed and broadened. The application of magnetic field of 5 T realizes 3D spin ordered state below Tc at atmospheric pressure. Both peak structure in χc and 3D spin ordered state are suppressed, and changes to 2D-like spin ordered state by increase of pressure. These results reveal that the pressure and the magnetic field are more competitive in altering the magnetic properties of bilayer manganite La1.25Sr1.75Mn2O7 single crystal.  相似文献   

16.
屈哲  皮雳  樊济宇  谭舜  张贝  张锰  张裕恒 《中国物理》2007,16(1):258-265
The double-doped La2/3+4x/3Sr1/3-4x/3Mn1-xMgxO3 samples with fixed Mn^3+/Mn^4+ ratio equal to 2/1 are investigated by means of magnetism and transport measurements. Phase separation is observed at temperature higher than T^onset c for x = 0.10 and 0.15. For x = 0.10, rather strong phase separation induces drastic magnetic random potential and results in the localization of carriers. Thus, the varlable-range hopping process dominates. For other samples, there is no or only weak phase separation above T^onset c. Thus, thermal activation mechanism is responsible for the high temperature transport behaviour. For x = 0.20 and 0.25, unexpected AFM behaviour is observed at low temperature. All these results are well understood by considering the special role of the "double-doping".  相似文献   

17.
Magnetic phase transitions in rare earth intermetallic compound Nd7Rh3 have been investigated using a single crystal. Measurement results of magnetization, magnetic susceptibility, specific heat, and electrical resistivity reveal that Nd7Rh3 has two magnetic phase transitions at TN=34 K, Tt2=9.1 K and a change of the magnetic feature at Tt1=6.8 K in the absence of an external magnetic field. Antiferromagnetic orderings exist in all the three magnetic states; a large magnetic anisotropy between the c-axis and the c-plane is observed. In the magnetic phase below Tt2, an irreversible field-induced magnetic phase transition takes place in the c-plane; after removing external magnetic field, a coexistence state of ferro- and antiferromagnetic ordering or a ferrimagnetic state having a remanent magnetization MR is stabilized. The MR decays to a certain value for several hours after the first process; a magnetic field cooling effect was also observed in the c-plane below Tt2. In the antiferromagentic state above Tt2, the irreversibility disappears and an ordinary antiferromagnetic state takes place. As the origin of this phenomenon, a kind of martensitic structural transition that is observed in Gd5Ge4 can be considered.  相似文献   

18.
王智河  曹效文  陈敬林  李可斌 《物理学报》1998,47(10):1720-1726
在0—7T磁场范围内,测量了不同测量电流密度下YBa2Cu3O7-δ外延薄膜的电阻温度关系.实验结果表明,临界温度以下,混合态的耗散电阻率能很好地用热激活磁通蠕动描述.有效钉扎势的电流密度关系遵守Zeldov等人提出的对数关系,有效钉扎势的温度和磁场关系遵守U∝(1-T/Tc)H关系,其中α=0.63,与热激活磁通点阵位错运动模型相一致,表明样品具有2D涡旋性质. 关键词:  相似文献   

19.
Using x-ray diffraction and magnetic measurements, we have studied the structural and magnetic properties of Dy2Co17-xMnx (x=0∽5) compounds with a rhombohedral Th2Zn17-type structure. With an increasing Mn concentration x, the unit-cell volume V was found to increase linearly. The Curie temperature Tc decreases linearly, and the saturation magnetization Ms at 5K first increases slightly for x<1, then decreases rapidly for x>1 with a further increase of Mn concentration x. In compounds for x=1~3, a spin reorientation was found. A magnetic diagram of the compounds is given.  相似文献   

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